Brain, other CNS or intracranial tumors are the ninth most common cancer in the UK (around 10,600 people were diagnosed in 2013), and it is the eighth most common cause of cancer death (around 5,200 people died in 2012).

Figures for incidences of cancers of the brain show a significant difference between more- and less-developed countries (the less-developed countries have lower incidences of tumors of the brain). This could be explained by undiagnosed tumor-related deaths (patients in extremely poor situations do not get diagnosed, simply because they do not have access to the modern diagnostic facilities required to diagnose a brain tumor) and by deaths caused by other poverty-related causes that preempt a patient's life before tumors develop or tumors become life-threatening. Nevertheless, studies suggest that certain forms of primary brain tumors are more prevalent among certain groups of the population.

The incidence of low-grade astrocytoma has not been shown to vary significantly with nationality. However, studies examining the incidence of malignant central nervous system (CNS) tumors have shown some variation with national origin. Since some high-grade lesions arise from low-grade tumors, these trends are worth mentioning. Specifically, the incidence of CNS tumors in the United States, Israel, and the Nordic countries is relatively high, while Japan and Asian countries have a lower incidence. These differences probably reflect some biological differences as well as differences in pathologic diagnosis and reporting.

Worldwide data on incidence of cancer can be found at the WHO (World Health Organisation) and is handled by the IARC (International Agency for Research on Cancer) located in France.

The most common sources of brain metastases in a case series of 2,700 patients undergoing treatment at the Memorial Sloan–Kettering Cancer Center were:

- Lung cancer, 48%

- Breast cancer, 15%

- Genitourinary tract cancers, 11%

- Osteosarcoma, 10%

- Melanoma, 9%

- Head and neck cancer, 6%

- Neuroblastoma, 5%

- Gastrointestinal cancers, especially colorectal and pancreatic carcinoma, 3%

- Lymphoma, 1%

Lung cancer and melanoma are most likely to present with multiple metastasis, whereas breast, colon, and renal cancers are more likely to present with a single metastasis.

The prognosis for brain metastases is variable. It depends on the type of primary cancer, the age of the patient, the absence or presence of extracranial metastases, and the number of metastatic sites in the brain. For patients who do not undergo treatment the average survival is between one and two months. However, in some patients, such as those with no extracranial metastases, those who are younger than 65, and those with a single site of metastasis in the brain only, prognosis is much better, with median survival rates of up to 13.5 months. Because brain metastasis can originate from various different primary cancers, the Karnofsky performance score is used for a more specific prognosis.

Adult survivors of childhood cancer have some physical, psychological, and social difficulties.

Premature heart disease is a major long-term complication in adult survivors of childhood cancer. Adult survivors are eight times more likely to die of heart disease than other people, and more than half of children treated for cancer develop some type of cardiac abnormality, although this may be asymptomatic or too mild to qualify for a clinical diagnosis of heart disease.

Children with cancer are at risk for developing various cognitive or learning problems. These difficulties may be related to brain injury stemming from the cancer itself, such as a brain tumor or central nervous system metastasis or from side effects of cancer treatments such as chemotherapy and radiation therapy. Studies have shown that chemo and radiation therapies may damage brain white matter and disrupt brain activity.

Other associations include exposure to smoking, pesticides, and working in petroleum refining or rubber manufacturing.

Glioblastoma has been associated with the viruses SV40, HHV-6, and cytomegalovirus.

About 3 per 100,000 people develop the disease a year. It most often begins around 64 years of age and occurs more commonly in males than females. It is the second most common central nervous system cancer after meningioma.

Factors that contribute to the development of hypopharyngeal cancer include:

- Smoking

- Chewing tobacco

- Heavy alcohol use

- Poor diet

Smoking, like lung cancer, can cause hypopharyngeal cancer because it contains carcinogens that alter the DNA or RNA in a dividing cell. These alterations may change a normal DNA sequence to an oncogene, a gene that causes cancer after exposure to a carcinogen.

Squamous cells, a type of cell that lines hollow organs like the throat, mouth, lungs, and outer layer of skin, are particularly vulnerable when exposed to cigarette smoke.

Chewing tobacco can have the same effects as smoking and is also linked to hypopharyngeal cancer. The chewing tobacco is placed into the mouth, leaving it exposed to enzymes, like amylase, which partly digests the carcinogenic material. Saliva is swallowed, along with the cancer-promoting material, which passes through the hypopharynx on its way to the esophagus.

Heavy alcohol use is linked to Hypopharyngeal Cancer as well. Alcohol damages the lining of the hypopharynx, increasing the amount of chemicals that are allowed to seep into the underlying membranes. Heavy alcohol use is also associated with nutritional deficiencies.

A disease called Plummer-Vinson syndrome, a genetic disorder that causes a long-term iron deficiency, may also lead to Hypopharyngeal Cancer. Other factors like a deficiency in certain vitamins also appear to contribute to this type of cancer.

Although metastasis is widely accepted to be the result of the tumor cells migration, there is a hypothesis saying that some metastases are the result of inflammatory processes by abnormal immune cells. The existence of metastatic cancers in the absence of primary tumors also suggests that metastasis is not always caused by malignant cells that leave primary tumors.

Smoking is the most important risk factor for laryngeal cancer. Death from laryngeal cancer is 20 times more likely for heaviest smokers than for nonsmokers. Heavy chronic consumption of alcohol, particularly alcoholic spirits, is also significant. When combined, these two factors appear to have a synergistic effect.

Some other quoted risk factors are likely, in part, to be related to prolonged alcohol and tobacco consumption. These include low socioeconomic status, male sex, and age greater than 55 years.

People with a history of head and neck cancer are known to be at higher risk (about 25%) of developing a second cancer of the head, neck, or lung. This is mainly because in a significant proportion of these patients, the aerodigestive tract and lung epithelium have been exposed chronically to the carcinogenic effects of alcohol and tobacco. In this situation, a field change effect may occur, where the epithelial tissues start to become diffusely dysplastic with a reduced threshold for malignant change. This risk may be reduced by quitting alcohol and tobacco.

Medulloblastomas affect just under two people per million per year, and affect children 10 times more than adults. Medulloblastoma is the second-most frequent brain tumor in children after pilocytic astrocytoma and the most common malignant brain tumor in children, comprising 14.5% of newly diagnosed cases. In adults, medulloblastoma is rare, comprising fewer than 2% of CNS malignancies.

The rate of new cases of childhood medulloblastoma is higher in males (62%) than females (38%), a feature which is not seen in adults. Medulloblastoma and other PNET`s are more prevalent in younger children than older children. About 40% of medulloblastoma patients are diagnosed before the age of five, 31% are between the ages of 5 and 9, 18.3% are between the ages of 10 and 14, and 12.7% are between the ages of 15 and 19.

The cumulative relative survival rate for all age groups and histology follow-up was 60%, 52%, and 47% at 5 years, 10 years, and 20 years, respectively. Patients diagnosed with a medulloblastoma or PNET are 50 times more likely to die than a matched member of the general population.

The most recent population-based (SEER) 5-year relative survival rates are 69% overall, but 72% in children (1–9 years) and 67% in adults (20+ years). The 20-year survival rate is 51% in children. Children and adults have different survival profiles, with adults faring worse than children only after the fourth year after diagnosis (after controlling for increased background mortality). Before the fourth year, survival probabilities are nearly identical. Longterm sequelae of standard treatment include hypothalamic-pituitary and thyroid dysfunction and intellectual impairment. The hormonal and intellectual deficits created by these therapies causes significant impairment of the survivors.

Smoking and alcohol abuse as the major risk factors. Viral causes has recently been taken under consideration as one of the risk factors. Viruses such as Epstein-Barr virus (EBV) (majorly involved in causing nasopharyngeal carcinoma) and human papilloma virus are included in this category. Chewing of betel nut ("Areca catechu") quid has been directly associated to cause oral cancers. It has also been stated under the FDA poisonous plant data base by the U.S Food and Drug Administration

An unbalanced diet, deficit in fruits and vegetables has shown to increase the risk of cancer.

An estimated 3% of pediatric brain tumors are AT/RTs, although this percentage may increase with better differentiation between PNET/medulloblastoma tumors and AT/RTs.

As with other CNS tumors, more males are affected than females (ratio 1.6:1). The ASCO study showed a 1.4:1 male to female ratio.

It is theorized that metastasis always coincides with a primary cancer, and, as such, is a tumor that started from a cancer cell or cells in another part of the body. However, over 10% of patients presenting to oncology units will have metastases without a primary tumor found. In these cases, doctors refer to the primary tumor as "unknown" or "occult," and the patient is said to have cancer of unknown primary origin (CUP) or unknown primary tumors (UPT). It is estimated that 3% of all cancers are of unknown primary origin. Studies have shown that, if simple questioning does not reveal the cancer's source (coughing up blood—"probably lung", urinating blood—"probably bladder"), complex imaging will not either. In some of these cases a primary tumor may appear later.

The use of immunohistochemistry has permitted pathologists to give an identity to many of these metastases. However, imaging of the indicated area only occasionally reveals a primary. In rare cases (e.g., of melanoma), no primary tumor is found, even on autopsy. It is therefore thought that some primary tumors can regress completely, but leave their metastases behind. In other cases, the tumor might just be too small and/or in an unusual location to be diagnosed.

While cancer is generally considered a disease of old age, children can also develop cancer. In contrast to adults, carcinomas are exceptionally rare in children..

The two biggest risk factors for ovarian carcinoma are age and family history.

There are no precise guidelines because the exact cause of astrocytoma is not known.

Metastatic spread is noted in roughly one-third of the AT/RT cases at the time of diagnosis, and tumors can occur anywhere throughout the CNS. The ASCO study of the 188 documented AT/RT cases prior to 2004 found 30% of the cases had metastasis at diagnosis. Metastatic spread to the meninges (leptomenigeal spread sometimes referred to as sugar coating) is common both initially and with relapse. Average survival times decline with the presence of metastasis. Primary CNS tumors generally metastasize only within the CNS.

One case of metastatic disease to the abdomen via ventriculoperitoneal shunt has been reported with AT/RT . Metastatic dissemination via this mechanism has been reported with other brain tumors, including germinomas, medulloblastomas, astrocytomas, glioblastomas, ependymomas, and endodermal sinus tumors. Guler and Sugita separately reported cases of lung metastasis without a shunt.

Astrocytomas are a type of cancer of the brain. They originate in a particular kind of glial cells, star-shaped brain cells in the cerebrum called astrocytes. This type of tumor does not usually spread outside the brain and spinal cord and it does not usually affect other organs. Astrocytomas are the most common glioma and can occur in most parts of the brain and occasionally in the spinal cord. Within the astrocytomas, there are two broad classes recognized in literature, those with:

- Narrow zones of infiltration (mostly noninvasive tumors; e.g., pilocytic astrocytoma, subependymal giant cell astrocytoma, pleomorphic xanthoastrocytoma), that often are clearly outlined on diagnostic images

- Diffuse zones of infiltration (e.g., high-grade astrocytoma, anaplastic astrocytoma, glioblastoma), that share various features, including the ability to arise at any location in the CNS (Central Nervous System), but with a preference for the cerebral hemispheres; they occur usually in adults; and an intrinsic tendency to progress to more advanced grades.

People can develop astrocytomas at any age. The low-grade type is more often found in children or young adults, while the high-grade type are more prevalent in adults. Astrocytomas in the base of the brain are more common in young people and account for roughly 75% of neuroepithelial tumors.

The ultraviolet radiation from tanning beds increases the risk of melanoma. The International Agency for Research on Cancer finds that tanning beds are "carcinogenic to humans" and that people who begin using tanning devices before the age of thirty years are 75% more likely to develop melanoma.

Those who work in airplanes also appear to have an increased risk, believed to be due to greater exposure to UV.

Ultraviolet UVB light (wavelengths between 315 – 280 nm) from the sun is absorbed by skin cell DNA and results in a type of direct DNA damage called cyclobutane pyrimidine dimers (CPDs). Thymine-thymine, cytosine-cytosine or cytosine-thymine dimers are formed by the joining of two adjacent pyrimidine bases within a DNA strand. Somewhat similarly to UVB, UVA light (longer wavelengths between 400 – 315 nm) from the sun or from tanning beds can also be directly absorbed by skin DNA (at about 100 to 1000 fold lower efficiency than UVB is absorbed).

Studies suggest that exposure to ultraviolet radiation (UVA and UVB) is one of the major contributors to the development of melanoma. Occasional extreme sun exposure (resulting in "sunburn") is causally related to melanoma. Melanoma is most common on the back in men and on legs in women (areas of intermittent sun exposure). The risk appears to be strongly influenced by socio-economic conditions rather than indoor versus outdoor occupations; it is more common in professional and administrative workers than unskilled workers. Other factors are mutations in or total loss of tumor suppressor genes. Use of sunbeds (with deeply penetrating UVA rays) has been linked to the development of skin cancers, including melanoma.

Possible significant elements in determining risk include the intensity and duration of sun exposure, the age at which sun exposure occurs, and the degree of skin pigmentation. Melanoma rates tend to be highest in countries settled by migrants from northern Europe that have a large amount of direct, intense sunlight that the skin of the settlers is not adapted to, most notably Australia. Exposure during childhood is a more important risk factor than exposure in adulthood. This is seen in migration studies in Australia.

Having multiple severe sunburns increases the likelihood that future sunburns develop into melanoma due to cumulative damage. The sun and tanning beds are the main sources of UV radiation that increase the risk for melanoma and living close to the equator increases exposure to UV radiation.

Most mammary tumors in rats are benign fibroadenomas, which are also the most common tumor in the rat. Less than 10 percent are adenocarcinomas. They occur in male and female rats. The tumors can be large and occur anywhere on the trunk. There is a good prognosis with surgery. Spayed rats have a decreased risk of developing mammary tumors.

Mammary tumors are the third most common neoplasia in cats, following lymphoid and skin cancers. The incidence of mammary tumors in cats is reduced by 91 percent in cats spayed prior to six months of age and by 86 percent in cats spayed prior to one year, according to one study. Siamese cats and Japanese breeds seem to have increased risk, and obesity also appears to be a factor in tumor development. Malignant tumors make up 80 to 96 percent of mammary tumors in cats, almost all adenocarcinomas. Male cats may also develop mammary adenocarcinoma, albeit rarely, and the clinical course is similar to female cats. As in dogs, tumor size is an important prognostic factor, although for tumors less than three centimeters the individual size is less predictive. According to one study, cats with tumors less than three cm had an average survival time of 21 months, and cats with tumors greater than three cm had an average survival of 12 months. About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time. Metastasis tends to be to the lungs and lymph nodes, and rarely to bone. Diagnosis and treatment is similar to the dog. There is a better prognosis with bilateral radical surgery (removing the both mammary chains) than with more conservative surgery. Doxorubicin has shown some promise in treatment.

Melanomas are usually caused by DNA damage resulting from exposure to ultraviolet light from the sun. Genetics also plays a role.

Having more than fifty moles indicates an increased risk melanoma might arise. A weakened immune system makes it easier for cancer to arise due to the body’s weakened ability to fight cancer cells.

Clinically symptomatic CNS metastases are reported in 10–15% of patients with metastatic breast cancer; in large autopsy studies, up to 40% of women who died of metastatic breast cancer were reported to have at least one brain metastasis. CNS metastases are often viewed by patients and doctors as a late complication of metastatic breast cancer for which few effective treatments exist. In most cases, CNS involvement occurs after metastatic dissemination to the bones, liver and/or lungs has already occurred; for that reason, many patients already have refractory, terminal breast cancer by the time they are diagnosed with brain metastases. The diagnosis of brain metastases from breast cancer relies mainly on patient-reported symptoms and neuroimaging. The role of imaging in patients with suspected brain metastases is a very good modality to aid in diagnosis. According to Weil et al., 2005, neuroimaging such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) prove to be very effective in the diagnosis of brain and central nervous system metastases.

Symptoms of brain metastases from breast cancer are:

- new-onset headache

- changes in mental status, cognition and behavior

- ataxia

- cranial neuropathy, which may cause diplopia and Bell's palsy

- vomiting and nausea

- deficits in sensation, motor function, and speech

Of all brain-metastatic patients, those with a controlled extra-cranial tumor, age less than 65 years and a favorable general performance (Karnofsky performance status ≥70) fare best; older patients with a Karnofsky performance status below 70 do poorly. Effective treatments for brain metastases from breast cancer exist, although symptomatic therapy alone may be chosen for those with poor performance status. Corticosteroids are crucial to the treatment of brain metastases from any source (including the breast), and are effective in reducing peri-tumoral edema and providing symptomatic relief. Chemotherapy has not been found to be effective in the treatment of brain metastases from breast cancer, due to the inability of most chemotheraputic agents to penetrate the blood–brain barrier. Whole-brain radiation may provide a median survival of 4 to 5 months, which can be further extended by months with stereotactic surgery. Several non-randomized studies have suggested that stereotactic surgery may provide a nearly equivalent outcome, compared with surgery followed by whole brain-irradiation. Surgery tends to reduce symptoms quickly and prolong life, with an improved quality of life. Multiple metastases (up to three) may be removed surgically with a risk similar to that of a single lesion, providing similar benefits. Adjuvant radiotherapy follows surgical resection; this combined approach has been shown to prolong median survival up to 12 months, depending on the factors noted above. There is evidence that surgery may be useful in select patients with recurrent brain metastases. Mean survival from diagnosis of a brain metastasis varies between studies, ranging from 2 to 16 months (depending on involvement of the CNS, the extent of the extra-cranial metastatic disease, and the treatment applied). The mean 1-year survival is estimated at 20%. Improvements in the treatment of brain metastases are clearly needed.