Cancer comprises a group of diseases that involve the uncontrolled growth of cells. The population of cells that bypass the body's complex regulation of growth is called a tumor. Since the body is predominantly composed of cell tissue, tumors can arise in virtually any part of the body, from the head to the foot.

Benign tumors are localized to a certain area of the body. Surgical or chemical treatment can often remove this class of tumors, and they usually do not return. Malignant tumors are cancerous cells that have emerged from their point of origin to affect other parts of the body. This spread of cancer is termed metastasis. Metastasis may occur via the blood or lymphatic system. Tissue biopsies of lymph nodes are oftentimes performed to detect whether cancerous cells have metastasized or progressed elsewhere in the body. Just one malignant cell is needed to form a new tumor, so aggressive treatment is generally prescribed.

Carcinomas are cancers that typically affect the epithelial linings of tissues. This may include areas such as the skin, the lungs, gastrointestinal tract, blood vessels. Sarcomas involve malignancies of the connective and supporting tissues, primarily derived from embryological mesoderm. Leukemias are cancers involving abnormal proliferation of lymphocytes.

Cancer is a multi-factorial disease, which is contributed by genetic and environmental influences. Cancer is not caused by injury and is not contagious. Through population studies, certain risk factors have been identified that can lead to cancer. Examples of these include family, age, tobacco, poor diet, excessive alcohol, radiation, chemicals, and hormone replacement therapy.

There are three therapeutic modalities in the treatment of cancer: surgery, radiation, and chemotherapy. Surgery involves the physical resection of the tumor and neighboring tissue to ensure that all cancerous cells are removed. It takes just one surviving cell to grow into a new tumor. Radiation is another form of therapy that began in the 1930s. Through the controlled spatial dosage of radiation, the radiation oncologist can selectively kill cancer cells while sparing good tissue. The above two forms of treatment are useful for localized and bulky cancers. Cancers that have spread require more systemic measures, such as chemotherapy. Through various mechanisms, these drugs can interfere with the growth or survival of cancer cells throughout the body.

Despite the rapid advances of cancer therapy, there is not yet a miracle drug that addresses all forms of cancer. The treatment plan for any patient is as unique as the patient himself or herself. Treatment choices are usually discussed by a team of physicians, such as in a "Tumor Board", to carefully weigh available options.

Cancer patients and their families are strongly advised to avoid outlandish claims by non-medical professionals who eagerly prey on people's desperation. There are reported claims of cure-alls that have been debunked scientifically and shown to have poor outcomes.