Cancer is known medically as malignant neoplasia is a broad group of diseases involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, which may invade nearby parts of the body.

Cancer may also spread to more distant parts of the body through the lymphatic system or bloodstream. Not all tumors are cancerous; benign tumors do not invade neighboring tissues and do not spread throughout the body.

There are over 200 different known cancers that affect humans.

The causes of cancer are diverse, complex, and only partially understood.

Many things are known to increase the risk of cancer, including tobacco use, dietary factors, certain infections, exposure to radiation, lack of physical activity, obesity, and environmental pollutants.

These factors can directly damage genes or combine with existing genetic faults within cells to cause cancerous mutations. Approximately 5–10% of cancers can be traced directly to inherited genetic defects.

Many cancers could be prevented by not smoking, eating more vegetables, fruits and whole grains, eating less meat and refined carbohydrates, maintaining a healthy weight, exercising, minimizing sunlight exposure, and being vaccinated against some infectious diseases.

Cancer can be detected in a number of ways, including the presence of certain signs and symptoms, screening tests, or medical imaging.

Once a possible cancer is detected it is diagnosed by microscopic examination of a tissue sample. Cancer is usually treated with chemotherapy, radiation therapy, and surgery.

The chances of surviving the disease vary greatly by the type and location of cancer and the extent of disease at the start of treatment.

While cancer can affect people of all ages, and a few types of cancer are more common in children, the risk of developing cancer generally increases with age.

Rates are rising as more people live to old age and as mass lifestyle changes occur in the developing world.[6]

When cancer begins, it invariably produces no symptoms. Signs and symptoms only appear as the mass continues to grow or ulcerates.

The findings that result depend on the type and location of cancer. Few symptoms are specific, with many of them also frequently occurring in individuals who have other conditions.

Local symptoms may occur due to the mass of the tumor or its ulceration.

For example, mass effects from lung cancer can cause blockage of the bronchus resulting in cough or pneumonia; esophageal cancer can cause narrowing of the esophagus, making it difficult or painful to swallow; and colorectal cancer may lead to narrowing or blockages in the bowel, resulting in changes in bowel habits.

Masses in breasts or testicles may be easily felt. Ulceration can cause bleeding which, if it occurs in the lung, will lead to coughing up blood, in the bowels to anemia or rectal bleeding, in the bladder to blood in the urine, and in the uterus to vaginal bleeding.

Although localized pain may occur in advanced cancer, the initial swelling is usually painless. Some cancers can cause a build-up of fluid within the chest or abdomen.

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, particularly in the aged, and include nearly all those developing in the breast, prostate, lung, pancreas, and colon.

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 of cancer arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively. Leukemia is the most common type of cancer in children accounting for about 30%.

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. Blastomas are more common in children than in older adults.

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 are called hepatocarcinoma, while a malignancy arising from primitive liver precursor cells is called a hepatoblastoma, and 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.

Pathology

The tissue diagnosis given by the pathologist indicates the type of cell that is proliferating, its histological grade, genetic abnormalities, and other features of the tumor.

Together, this information is useful to evaluate the prognosis of the patient and to choose the best treatment.
Cytogenetics and immunohistochemistry are other types of testing that the pathologist may perform on the tissue specimen.

These tests may provide information about the molecular changes (such as mutations, fusion genes, and numerical chromosome changes) that has happened in the cancer cells, and may thus also indicate the future behavior of cancer (prognosis) and best treatment.

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