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cancer — news, coverage & facts — IJR

Physical agents

Some substances cause cancer primarily through their physical, rather than chemical, effects. A prominent example of this is prolonged exposure to asbestos, naturally occurring mineral fibers that are a major cause of mesothelioma (cancer of the serous membrane) usually the serous membrane surrounding the lungs. Other substances in this category, including both naturally occurring and synthetic asbestos-like fibers, such as wollastonite, attapulgite, glass wool and rock wool, are believed to have similar effects. Non-fibrous particulate materials that cause cancer include powdered metallic cobalt and nickel and crystalline silica (quartz, cristobalite and tridymite). Usually, physical carcinogens must get inside the body (such as through inhalation) and require years of exposure to produce cancer.

Physical trauma resulting in cancer is relatively rare. Claims that breaking bones resulted in bone cancer, for example, have not been proven. Similarly, physical trauma is not accepted as a cause for cervical cancer, breast cancer or brain cancer. One accepted source is frequent, long-term application of hot objects to the body. It is possible that repeated burns on the same part of the body, such as those produced by kanger and kairo heaters (charcoal hand warmers), may produce skin cancer, especially if carcinogenic chemicals are also present. Frequent consumption of scalding hot tea may produce esophageal cancer. Generally, it is believed that cancer arises, or a pre-existing cancer is encouraged, during the process of healing, rather than directly by the trauma. However, repeated injuries to the same tissues might promote excessive cell proliferation, which could then increase the odds of a cancerous mutation.

Chronic inflammation has been hypothesized to directly cause mutation. Inflammation can contribute to proliferation, survival, angiogenesis and migration of cancer cells by influencing the tumor microenvironment. Oncogenes build up an inflammatory pro-tumorigenic microenvironment.

Genetics

Cancer is fundamentally a disease of tissue growth regulation. For a normal cell to transform into a cancer cell, the genes that regulate cell growth and differentiation must be altered.

The affected genes are divided into two broad categories. Oncogenes are genes that promote cell growth and reproduction. Tumor suppressor genes are genes that inhibit cell division and survival. Malignant transformation can occur through the formation of novel oncogenes, the inappropriate over-expression of normal oncogenes, or by the under-expression or disabling of tumor suppressor genes. Typically, changes in multiple genes are required to transform a normal cell into a cancer cell.

Genetic changes can occur at different levels and by different mechanisms. The gain or loss of an entire chromosome can occur through errors in mitosis. More common are mutations, which are changes in the nucleotide sequence of genomic DNA.

Large-scale mutations involve the deletion or gain of a portion of a chromosome. Genomic amplification occurs when a cell gains copies (often 20 or more) of a small chromosomal locus, usually containing one or more oncogenes and adjacent genetic material. Translocation occurs when two separate chromosomal regions become abnormally fused, often at a characteristic location. A well-known example of this is the Philadelphia chromosome, or translocation of chromosomes 9 and 22, which occurs in chronic myelogenous leukemia and results in production of the BCR-Abl fusion protein, an oncogenic tyrosine kinase.

Small-scale mutations include point mutations, deletions, and insertions, which may occur in the promoter region of a gene and affect its expression, or may occur in the gene's coding sequence and alter the function or stability of its protein product. Disruption of a single gene may also result from integration of genomic material from a DNA virus or retrovirus, leading to the expression of viral oncogenes in the affected cell and its descendants.

Replication of the data contained within the DNA of living cells will probabilistically result in some errors (mutations). Complex error correction and prevention are built into the process and safeguard the cell against cancer. If a significant error occurs, the damaged cell can self-destruct through programmed cell death, termed apoptosis. If the error control processes fail, then the mutations will survive and be passed along to daughter cells.

Some environments make errors more likely to arise and propagate. Such environments can include the presence of disruptive substances called carcinogens, repeated physical injury, heat, ionising radiation, or hypoxia.

The errors that cause cancer are self-amplifying and compounding, for example:

A mutation in the error-correcting machinery of a cell might cause that cell and its children to accumulate errors more rapidly.

A further mutation in an oncogene might cause the cell to reproduce more rapidly and more frequently than its normal counterparts.

A further mutation may cause the loss of a tumor suppressor gene, disrupting the apoptosis signaling pathway and immortalizing the cell.

A further mutation in the signaling machinery of the cell might send error-causing signals to nearby cells.

The transformation of a normal cell into cancer is akin to a chain reaction caused by initial errors, which compound into more severe errors, each progressively allowing the cell to escape more controls that limit normal tissue growth. This rebellion-like scenario is an undesirable survival of the fittest, where the driving forces of evolution work against the body's design and enforcement of order. Once cancer has begun to develop, this ongoing process, termed clonal evolution, drives progression towards more invasive stages. Clonal evolution leads to intra-tumour heterogeneity (cancer cells with heterogeneous mutations) that complicates the design of effective treatments, as therapies must account for the selective pressures they exert on the tumour cell population.

Characteristic abilities developed by cancers are divided into categories, specifically evasion of apoptosis, replicating independently of external growth signals, insensitivity to anti-growth signals, sustained blood vessel formation, limitless replicative potential, spreading to other parts of the body (metastasis), reprogramming of energy metabolism and evasion of immune destruction.

Epigenetics

The classical view of cancer is a set of diseases driven by progressive genetic abnormalities that include mutations in tumor-suppressor genes and oncogenes, and in chromosomal abnormalities. A role for epigenetic alterations was identified in the early 21st century.

Epigenetic alterations are functionally relevant modifications to the genome that do not change the nucleotide sequence. Examples of such modifications are changes in DNA methylation (hypermethylation and hypomethylation), histone modification and changes in chromosomal architecture (caused by inappropriate expression of proteins such as HMGA2 or HMGA1). Each of these alterations regulates gene expression without altering the underlying DNA sequence. These changes may remain through cell divisions, endure for multiple generations, and can be considered as equivalent to mutations.

Epigenetic alterations occur frequently in cancers. As an example, one study listed protein coding genes that were frequently altered in their methylation in association with colon cancer. These included 147 hypermethylated and 27 hypomethylated genes. Of the hypermethylated genes, 10 were hypermethylated in 100% of colon cancers and many others were hypermethylated in more than 50% of colon cancers.

While epigenetic alterations are found in cancers, the epigenetic alterations in DNA repair genes, causing reduced expression of DNA repair proteins, may be of particular importance. Such alterations may occur early in the progression to cancer and are a possible cause of the genetic instability characteristic of cancers.

Reduced expression of DNA repair genes disrupts DNA repair. This is shown in the figure at the 4th level from the top. (In the figure, red wording indicates the central role of DNA damage and defects in DNA repair in the progression to cancer.) When DNA repair is deficient DNA damage remains in cells at a higher than usual level (5th level) and causes increased frequencies of mutation and/or epimutation (6th level). Mutation rates increase substantially in cells defective in DNA mismatch repair or in homologous recombinational repair (HRR). Chromosomal rearrangements and aneuploidy (an abnormal number of chromosomes in a cell) also increase in HRR defective cells.

Higher levels of DNA damage cause increased mutation (right side of figure) and increased epimutation. During repair of DNA double strand breaks, or repair of other DNA damage, incompletely cleared repair sites can cause epigenetic gene silencing.

Deficient expression of DNA repair proteins due to an inherited mutation can increase cancer risks. Individuals with an inherited impairment in any of 34 DNA repair genes (see article DNA repair-deficiency disorder) have increased cancer risk, with some defects ensuring a 100% lifetime chance of cancer (e.g. p53 mutations). Germline DNA repair mutations are noted on the figure's left side. However, such germline mutations (which cause highly penetrant cancer syndromes) are the cause of only about 1 percent of cancers.

In sporadic cancers, deficiencies in DNA repair are occasionally caused by a mutation in a DNA repair gene but are much more frequently caused by epigenetic alterations that reduce or silence expression of DNA repair genes. This is indicated in the figure at the 3rd level. Many studies of heavy metal-induced carcinogenesis show that such heavy metals cause a reduction in expression of DNA repair enzymes, some through epigenetic mechanisms. DNA repair inhibition is proposed to be a predominant mechanism in heavy metal-induced carcinogenicity. In addition, frequent epigenetic alterations of the DNA sequences code for small RNAs called microRNAs (or miRNAs). miRNAs do not code for proteins, but can "target" protein-coding genes and reduce their expression.

Cancers usually arise from an assemblage of mutations and epimutations that confer a selective advantage leading to clonal expansion (see Field defects in progression to cancer). Mutations, however, may not be as frequent in cancers as epigenetic alterations. An average cancer of the breast or colon can have about 60 to 70 protein-altering mutations, of which about three or four may be "driver" mutations and the remaining ones may be "passenger" mutations.

Classification

Cancers are classified by the type of cell that the tumor cells resemble and is therefore presumed to be the origin of the tumor. These types include:

Carcinoma: Cancers derived from epithelial cells. This group includes many of the most common cancers and include nearly all those in the breast, prostate, lung, pancreas and colon. Most of these are of the adenocarcinoma type, which means that the cancer has gland-like differentiation.

Sarcoma: Cancers arising from connective tissue (i.e. bone, cartilage, fat, nerve), each of which develops from cells originating in mesenchymal cells outside the bone marrow.

Lymphoma and leukemia: These two classes arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively.

Germ cell tumor: Cancers derived from pluripotent cells, most often presenting in the testicle or the ovary (seminoma and dysgerminoma, respectively).

Blastoma: Cancers derived from immature "precursor" cells or embryonic tissue.

Cancers are usually named using -carcinoma, -sarcoma or -blastoma as a suffix, with the Latin or Greek word for the organ or tissue of origin as the root. For example, cancers of the liver parenchyma arising from malignant epithelial cells is called hepatocarcinoma, while a malignancy arising from primitive liver precursor cells is called a hepatoblastoma and a cancer arising from fat cells is called a liposarcoma. For some common cancers, the English organ name is used. For example, the most common type of breast cancer is called ductal carcinoma of the breast. Here, the adjective ductal refers to the appearance of cancer under the microscope, which suggests that it has originated in the milk ducts.

Benign tumors (which are not cancers) are named using -oma as a suffix with the organ name as the root. For example, a benign tumor of smooth muscle cells is called a leiomyoma (the common name of this frequently occurring benign tumor in the uterus is fibroid). Confusingly, some types of cancer use the -noma suffix, examples including melanoma and seminoma.

Some types of cancer are named for the size and shape of the cells under a microscope, such as giant cell carcinoma, spindle cell carcinoma and small-cell carcinoma.

Environment

Ultraviolet radiation is the main cause of skin cancer. The incidence of skin cancer is increasing, and it is the most common type of cancer in lighter-skinned populations. UV radiation, whether from sunlight or tanning beds, directly and indirectly damages DNA.

The most effective way to prevent skin cancer is to limit sun exposure and not use tanning beds, wear protective clothing (such as a hat), wear sunscreen, and make use of the shade. The best time to avoid sunlight is between 9:00 a.m. and 3:00 p.m. when UV radiation is strongest. Even on cloudy days about 80% of UV radiation is still present. UV radiation does not correlate with temperature—there is just as much UV radiation from the sun on a cold day as on a hot day. About 10% of UVB radiation passes through glass windows.

UV exposure during childhood is particularly harmful. However, the beneficial effects of sunlight exposure (such as the production of vitamin D) can be achieved while avoiding harmful amounts of sun exposure.

The ozone layer absorbs UV radiation from the sun, reducing rates of skin cancer. However, atmospheric pollution has decreased the ozone layer, and increased rates of skin cancer globally. In 1987, an international treaty named the Montreal Protocol was signed to limit the release of ozone-damaging chemicals. Since then the ozone layer has been recovering, and it is expected that by 2100 the Montreal Protocol will have prevented 11 million cases of melanoma in the United States.

Air pollution, both outdoor and indoor, is the largest environmental contributor to cancer. Air pollution caused an estimated 350,167 deaths from lung cancer in 2017.

Airborne particulate matter smaller than 2.5 µm (PM2.5) is a group 1 carcinogen. The concentration of PM2.5 in the air is the most reliable predictor of how carcinogenic the air is. PM2.5 primarily comes from the burning of fuel for transportation, power generation, and industry, the burning of biomass (e.g. forest fires, stubble burning), and heating and cooking in the home. In 2017, an estimated 14.1% of all lung cancer deaths were caused by PM2.5 pollution.

Local PM2.5 and PM10 levels can be monitored online, and wearing a close-fitting particulate respirator reduces personal exposure when levels are high. Exposure to cancer-causing air pollution can also be reduced by avoiding motorized transportation, selecting routes away from pollution sources such as coal plants, and keeping vehicle windows closed in heavy traffic.

Decreasing outdoor air pollution requires action on the public policy level, and involves international collaborative efforts.

Indoor air pollution includes PM2.5 from the burning of fuels, as well as other pollutants such as radon and hazardous construction materials (e.g. asbestos, glues, formaldehyde, lead). In 2019, the percent of preventable cases of lung cancer by cause was estimated as 62% for smoking, 15% for PM2.5 in outdoor air, 5.8% for secondhand smoke, 4% from using solid fuels for cooking, and 4% for radon. Individuals can decrease air pollution in the home by using clean fuels, maintaining adequate ventilation, and using air purifiers.

Around 80% of ionizing radiation that people are exposed to comes from natural sources, around half of which comes from breathing in radioactive radon gas. Radon is produced by the decay of uranium in the ground, becoming a radioactive gas that can accumulate in the buildings above it. Exposure to radon can be reduced by testing homes and, when found to be high, taking steps to reduce indoor radon levels.

The primary method to reduce indoor radon levels is a vent pipe system and fan, which pulls radon from beneath the building and vents it to the outside.

Around 20% of ionizing radiation that people are exposed to comes from artificial sources, primarily from x-rays used for medical imaging. CT scans, which take x-rays at many angles to produce a 3D image, expose patients to a higher level of radiation than standard 2D x-rays. Cancer prevention focuses on avoiding unnecessary diagnostic procedures, and minimizing the dose of ionizing radiation that patients are exposed to during these procedures.

There have been 38 workplace chemicals and 12 workplace circumstances classified as carcinogenic, and 41 chemicals and 6 circumstances classified as probably carcinogenic. Despite being known to cause cancer, workers are still commonly exposed to silica, diesel engine exhaust, heavy metals, asbestos, and polycyclic aromatic hydrocarbons.

Occupational cancer can be reduced, and in recent decades successful regulations and programs have reduced or eliminated exposure to certain carcinogens in the workplace. Prevention involves decreasing the use of certain chemicals and if this isn't possible limiting exposure to these substances, a process known as hierarchy of controls.

Occupational cancer can also be prevented by improving workplace procedures and training, and by using personal protective equipment.

Medical

In 2018, 2.2 million cases of cancer were caused by infection, primarily by Helicobacter pylori (810,000), human papillomavirus (690,000), hepatitis B (360,000), and hepatitis C (160,000). All four of these infections can either be vaccinated against or treated, and collectively they cause more than 90% of infection-related cancers worldwide.

Helicobacter pylori, the bacteria responsible for most cases of stomach ulcers, can also cause stomach cancer. Treatment of Helicobacter pylori with antibiotics may help prevent stomach cancer. Almost all cases of cervical cancer are caused by the human papillomavirus, which can be vaccinated against (Gardasil and Cervarix). Hepatitis B and hepatitis C are responsible for 3/4 of the most common type of liver cancer. A vaccine for the hepatitis B virus has been available since 1982, and more than 95% of people with hepatitis C can be cured with antiviral drugs.

Medications can be used to prevent cancer in a few circumstances. In the general population, NSAIDs reduce the risk of colorectal cancer; however, due to cardiovascular and gastrointestinal side effects, they cause more harm than benefit when used for prevention. Aspirin is not recommended for reducing cancer risk. COX-2 inhibitors may decrease the rate of polyp formation in people with familial adenomatous polyposis; however, it is associated with the same adverse effects as NSAIDs.

Women who have an increased risk for breast cancer can lower their chances of getting breast cancer by taking tamoxifen, raloxifene, or aromatase inhibitors.

No vitamin, multivitamin, or nutritional supplement is recommended for the prevention of cancer. Vitamin E supplements do not prevent cancer, and beta-carotene supplements increase the odds of lung cancer in those already at a high risk for it.

Hormone-sensitive cancers are dependent on hormones for growth and survival. Medications that effect hormone levels may therefore have a harmful or beneficial effect on cancer rates. Women who are on, or recently took, combined oral contraceptives (COCs) have an increased risk for breast cancer and cervical cancer. However, CBCs also decrease the risk for ovarian cancer, and this protective effect continues years after stopping their use.

Estrogen-only menopausal hormone therapy increases the risk of breast, endometrial, and ovarian cancer. Combined estrogen–progestogen hormone therapy increases the risk of breast and endometrial cancer.

Chemotherapy

Chemotherapy is the treatment of cancer with one or more cytotoxic anti-neoplastic drugs (chemotherapeutic agents) as part of a standardized regimen. The term encompasses a variety of drugs, which are divided into broad categories such as alkylating agents and antimetabolites. Traditional chemotherapeutic agents act by killing cells that divide rapidly, a critical property of most cancer cells.

It was found that providing combined cytotoxic drugs is better than a single drug, a process called the combination therapy, which has an advantage in the statistics of survival and response to the tumor and in the progress of the disease. A Cochrane review concluded that combined therapy was more effective in treating metastasized breast cancer. However, generally it is not certain whether combination chemotherapy leads to better health outcomes, when both survival and toxicity are considered.

Targeted therapy is a form of chemotherapy that targets specific molecular differences between cancer and normal cells. The first targeted therapies blocked the estrogen receptor molecule, inhibiting the growth of breast cancer. Another common example is the class of Bcr-Abl inhibitors, which are used to treat chronic myelogenous leukemia (CML). Currently, targeted therapies exist for many of the most common cancer types, including bladder cancer, breast cancer, colorectal cancer, kidney cancer, leukemia, liver cancer, lung cancer, lymphoma, pancreatic cancer, prostate cancer, skin cancer, and thyroid cancer as well as other cancer types.

The efficacy of chemotherapy depends on the type of cancer and the stage. In combination with surgery, chemotherapy has proven useful in cancer types including breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer and certain lung cancers. Chemotherapy is curative for some cancers, such as some leukemias, ineffective in some brain tumors, and needless in others, such as most non-melanoma skin cancers. The effectiveness of chemotherapy is often limited by its toxicity to other tissues in the body. Even when chemotherapy does not provide a permanent cure, it may be useful to reduce symptoms such as pain or to reduce the size of an inoperable tumor in the hope that surgery will become possible in the future.Wang M, Zhang C, Yang G, Shi Y (March 2017). "Neoadjuvant Chemotherapy Creates Surgery Opportunities For Inoperable Locally Advanced Breast Cancer". Scientific Reports. 7 (3) 44673. Bibcode:2017NatSR...744673W. doi:10.1038/srep44673. PMC 5361098. PMID 28322234.

Prognosis

Survival rates vary by cancer type and by the stage at which it is diagnosed, ranging from majority survival to complete mortality five years after diagnosis. Once a cancer has metastasized, prognosis normally becomes much worse. About half of patients receiving treatment for invasive cancer (excluding carcinoma in situ and non-melanoma skin cancers) die from that cancer or its treatment. A majority of cancer deaths are due to metastases of the primary tumor.

Survival is worse in the developing world, partly because the types of cancer that are most common there are harder to treat than those associated with developed countries.

Those who survive cancer develop a second primary cancer at about twice the rate of those never diagnosed. The increased risk is believed to be due to the random chance of developing any cancer, the likelihood of surviving the first cancer, the same risk factors that produced the first cancer, unwanted side effects of treating the first cancer (particularly radiation therapy), and better compliance with screening.

Predicting short- or long-term survival depends on many factors. The most important are the cancer type and the patient's age and overall health. Those who are frail with other health problems have lower survival rates than otherwise healthy people. Centenarians are unlikely to survive for five years even if treatment is successful. People who report a higher quality of life tend to survive longer. People with lower quality of life may be affected by depression and other complications and/or disease progression that both impairs quality and quantity of life. Additionally, patients with worse prognoses may be depressed or report poorer quality of life because they perceive that their condition is likely to be fatal.Satin JR, Linden W, Phillips MJ (November 2009). "Depression as a predictor of disease progression and mortality in cancer patients: a meta-analysis". Cancer. 115 (22): 5349–61. doi:10.1002/cncr.24561. PMID 19753617.

People with cancer have an increased risk of blood clots in their veins which can be life-threatening. The use of blood thinners such as heparin decrease the risk of blood clots but have not been shown to increase survival in people with cancer. People who take blood thinners also have an increased risk of bleeding.

Although extremely rare, some forms of cancer, even from an advanced stage, can heal spontaneously. This phenomenon is known as spontaneous remission.

Epidemiology

Estimates are that in 2018, 18.1 million new cases of cancer and 9.6 million deaths occur globally. About 20% of males and 17% of females will get cancer at some point in time while 13% of males and 9% of females will die from it.

In 2008, approximately 12.7 million cancers were diagnosed (excluding non-melanoma skin cancers and other non-invasive cancers) and in 2010 nearly 7.98 million people died. Cancers account for almost one in six deaths. The cancers causing the most deaths, as of 2020 are lung cancer (1.8 million), colorectal cancer (916,000), liver cancer (830,000), stomach cancer (769,000) and breast cancer (685,000). This makes invasive cancer the leading cause of death in the developed world and the second leading in the developing world. Over half of these cases occur in the developing world.

Deaths from cancer were 5.8 million in 1990. Deaths have been increasing primarily due to longer lifespans and lifestyle changes in the developing world. The most significant risk factor for developing cancer is age. Although it is possible for cancer to strike at any age, most patients with invasive cancer are over 65. According to cancer researcher Robert A. Weinberg, "If we lived long enough, sooner or later we all would get cancer." Some of the association between aging and cancer is attributed to immunosenescence, errors accumulated in DNA over a lifetime and age-related changes in the endocrine system. Aging's effect on cancer is complicated by factors such as DNA damage and inflammation promoting it and factors such as vascular aging and endocrine changes inhibiting it.

Some slow-growing cancers are particularly common, but often are not fatal. Autopsy studies in Europe and Asia showed that up to 36% of people have undiagnosed and apparently harmless thyroid cancer at the time of their deaths and that 80% of men develop prostate cancer by age 80. As these cancers do not cause the patient's death, identifying them would have represented overdiagnosis rather than useful medical care.Lowenstein LM, Basourakos SP, Williams MD, Troncoso P, Gregg JR, Thompson TC, et al. (March 2019). "Active surveillance for prostate and thyroid cancers: evolution in clinical paradigms and lessons learned". Nature Reviews. Clinical Oncology. 16 (3): 168–184. doi:10.1038/s41571-018-0116-x. PMC 6501050. PMID 30413793.

The three most common childhood cancers are leukemia (34%), brain tumors (23%) and lymphomas (12%). In the United States, cancer affects about 1 in 285 children. Rates of childhood cancer increased by 0.6% per year between 1975 and 2002 in the United States and by 1.1% per year between 1978 and 1997 in Europe. Death from childhood cancer decreased by half between 1975 and 2010 in the United States.

History

Cancer has existed for all of human history. The earliest written record regarding cancer is from c. 1600 BC in the Egyptian Edwin Smith Papyrus and describes breast cancer. Hippocrates (c. 460 BC – c. 370 BC) described several kinds of cancer, referring to them with the Greek word καρκίνος karkinos (crab or crayfish). This name comes from the appearance of the cut surface of a solid malignant tumor, with "the veins stretched on all sides as the animal the crab has its feet, whence it derives its name". Galen stated that "cancer of the breast is so called because of the fancied resemblance to a crab given by the lateral prolongations of the tumor and the adjacent distended veins". Celsus (c. 25 BC – 50 AD) translated karkinos into Latin as cancer, also meaning crab and recommended surgery as treatment. Galen (2nd century AD) disagreed with the use of surgery and recommended purgatives instead. These recommendations largely stood for 1000 years.

In the 15th, 16th and 17th centuries, it became acceptable for doctors to dissect bodies to discover the cause of death. The German professor Wilhelm Fabry believed that breast cancer was caused by a milk clot in a mammary duct. The Dutch professor Francois de la Boe Sylvius, a follower of Descartes, believed that all disease was the outcome of chemical processes and that acidic lymph fluid was the cause of cancer. His contemporary Nicolaes Tulp believed that cancer was a poison that slowly spreads and concluded that it was contagious.

The physician John Hill described tobacco sniffing as the cause of nose cancer in 1761. This was followed by the report in 1775 by British surgeon Percivall Pott that chimney sweeps' carcinoma, a cancer of the scrotum, was a common disease among chimney sweeps. With the widespread use of the microscope in the 18th century, it was discovered that the 'cancer poison' spread from the primary tumor through the lymph nodes to other sites ("metastasis"). This view of the disease was first formulated by the English surgeon Campbell De Morgan between 1871 and 1874.

Society and culture

Although many diseases (such as heart failure) may have a worse prognosis than most cases of cancer, cancer is the subject of widespread fear and taboos. The euphemism of "a long illness" to describe cancers leading to death is still commonly used in obituaries, rather than naming the disease explicitly, reflecting an apparent stigma. Cancer is also euphemised as "the C-word"; Macmillan Cancer Support uses the term to try to lessen the fear around the disease. In Nigeria, one local name for cancer translates into English as "the disease that cannot be cured". This deep belief that cancer is necessarily a difficult and usually deadly disease is reflected in the systems chosen by society to compile cancer statistics: the most common form of cancer—non-melanoma skin cancers, accounting for about one-third of cancer cases worldwide, but very few deaths—are excluded from cancer statistics specifically because they are easily treated and almost always cured, often in a single, short, outpatient procedure.

Western conceptions of patients' rights for people with cancer include a duty to fully disclose the medical situation to the person, and the right to engage in shared decision-making in a way that respects the person's own values. In other cultures, other rights and values are preferred. For example, most African cultures value whole families rather than individualism. In parts of Africa, a diagnosis is commonly made so late that cure is not possible, and treatment, if available at all, would quickly bankrupt the family. As a result of these factors, African healthcare providers tend to let family members decide whether, when and how to disclose the diagnosis, and they tend to do so slowly and circuitously, as the person shows interest and an ability to cope with the grim news. People from Asian and South American countries also tend to prefer a slower, less candid approach to disclosure than is idealized in the United States and Western Europe, and they believe that sometimes it would be preferable not to be told about a cancer diagnosis. In general, disclosure of the diagnosis is more common than it was in the 20th century, but full disclosure of the prognosis is not offered to many patients around the world.

In the United States and some other cultures, cancer is regarded as a disease that must be "fought" to end the "civil insurrection"; a war on cancer was declared in the US. Military metaphors are particularly common in descriptions of cancer's human effects, and they emphasize both the state of the patient's health and the need to take immediate, decisive actions himself rather than to delay, to ignore or to rely entirely on others. The military metaphors also help rationalize radical, destructive treatments.

In the 1970s, a relatively popular alternative cancer treatment in the US was a specialized form of talk therapy, based on the idea that cancer was caused by a bad attitude. People with a "cancer personality"—depressed, repressed, self-loathing and afraid to express their emotions—were believed to have manifested cancer through subconscious desire. Some psychotherapists claimed that treatment to change the patient's outlook on life would cure the cancer. Among other effects, this belief allowed society to blame the victim for having caused the cancer (by "wanting" it) or having prevented its cure (by not becoming a sufficiently happy, fearless and loving person). It also increased patients' anxiety, as they incorrectly believed that natural emotions of sadness, anger or fear shorten their lives. The idea was ridiculed by Susan Sontag, who published Illness as Metaphor while recovering from treatment for breast cancer in 1978. Although the original idea is now generally regarded as nonsense, the idea partly persists in a reduced form with a widespread, but incorrect, belief that deliberately cultivating a habit of positive thinking will increase survival. This notion is particularly strong in breast cancer culture.

One idea about why people with cancer are blamed or stigmatized, called the just-world fallacy, is that blaming cancer on the patient's actions or attitudes allows the blamers to regain a sense of control. This is based upon the blamers' belief that the world is fundamentally just and so any dangerous illness, like cancer, must be a type of punishment for bad choices, because in a just world, bad things would not happen to good people.

Pregnancy

Cancer affects approximately 1 in 1,000 pregnant women. The most common cancers found during pregnancy are the same as the most common cancers found in non-pregnant women during childbearing ages: breast cancer, cervical cancer, leukemia, lymphoma, melanoma, ovarian cancer and colorectal cancer.

Diagnosing a new cancer in a pregnant woman is difficult, in part because any symptoms are commonly assumed to be a normal discomfort associated with pregnancy. As a result, cancer is typically discovered at a somewhat later stage than average. Some imaging procedures, such as MRIs (magnetic resonance imaging), CT scans, ultrasounds and mammograms with fetal shielding are considered safe during pregnancy; some others, such as PET scans, are not.

Treatment is generally the same as for non-pregnant women. However, radiation and radioactive drugs are normally avoided during pregnancy, especially if the fetal dose might exceed 100 cGy. In some cases, some or all treatments are postponed until after birth if the cancer is diagnosed late in the pregnancy. Early deliveries are often used to advance the start of treatment. Surgery is generally safe, but pelvic surgeries during the first trimester may cause miscarriage. Some treatments, especially certain chemotherapy drugs given during the first trimester, increase the risk of birth defects and pregnancy loss (spontaneous abortions and stillbirths).

Elective abortions are not required and, for the most common forms and stages of cancer, do not improve the mother's survival. In a few instances, such as advanced uterine cancer, the pregnancy cannot be continued and in others, the patient may end the pregnancy so that she can begin aggressive chemotherapy.

Some treatments can interfere with the mother's ability to give birth vaginally or to breastfeed. Cervical cancer may require birth by Caesarean section. Radiation to the breast reduces the ability of that breast to produce milk and increases the risk of mastitis. Also, when chemotherapy is given after birth, many of the drugs appear in breast milk, which could harm the baby.

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