Cancer starts in our cells. Cells are the small building blocks that come together to form the organs and tissues in our body. In general, cells divide to form new cells in a controlled fashion. That is how our body is able to grow, heal, and repair itself.

However, this process sometimes goes wrong, and some abnormal cells develop. Abnormal cells then divide, thus creating more and more abnormal cells. These cells form a growth, which is called a tumor.

Not all growths are cancerous.

A growth that isn't cancerous (i.e., a benign growth) cannot spread to other parts of the body.

On the other hand, if a growth is cancer (i.e., malignant), it can grow in nearby tissues.

Cancerous cells sometimes break off from the primary cancer site and travel to other parts of the body through the blood or the lymphatic system. When cancerous cells spread and come together to form a tumor in another part of the body, this is called secondary cancer.


It is important for your doctors to know what kind of cancer you have. Different cancer types are generally determined by the part of the body the tumor is in and the type of cells that make up the tumor.

The most common sites where cancer develops include the skin, lungs, breasts, prostate, colon, and rectum.

The three main types of cells that cancers start in are as follows:

  • Epithelial cells. Cancers that start in these cells are called carcinomas. About 80-90% of all cancer cases are carcinomas.
  • The cells of the blood and lymphatic system. Cancers that develop in this type of cells are called leukemias and lymphomas. Leukemias and lymphomas make up about 7% of all cancer cases.
  • Cells of connective tissue. Cancers that develop in these cells are called sarcomas. About 1% of all cancers are sarcomas.

Cancer can develop in other types of cells, but this happens only rarely.


Some cancer treatments target a particular area of the body. These are called localized treatments.

  • Surgery. The main treatment approach for many types of cancer is surgical removal of the tumor. This method is normally used for cancers found in one particular part of the body.
  • Radiotherapy. High-energy radiation is used to destroy the cancer cells. As this radiation is directed to the affected part of the body, there is risk of slight damage to healthy cells.

Other treatment approaches treat the entire body. This is called systemic treatment.

  • Chemotherapy. Chemotherapy is the administration of cancer-fighting medication (cytotoxic drugs) to destroy cancer cells. There are many types of chemotherapy drugs, and the choice of which one to use depends on the type of cancer the patient has.
  • Hormone therapy. Hormone therapy reduces hormone levels in the body or blocks hormones from affecting cancer cells. Doing so may slow the cancer's growth.
  • Targeted therapies. This type of therapy destroys cancer cells, mostly by interfering with the cancer's ability to grow or survive.

It is common for a patient to receive a combination of these therapies.


When cancer is first diagnosed, a treatment strategy is established to eliminate it. Either one treatment type or a combination of therapy approaches is used in order to reduce the likelihood that the cancer cells can survive.

Sometimes, however, cancer cells remain after therapy. If this happens, the cancer may return. Cancer can even come back years after the initial treatment. It can reappear either in the same area of the body or in another part.

  • Recurrence in the same part of the body is known as local recurrence.
  • When cancer comes back in another part of the body, it is called metastasis, or secondary cancer.

In general, certain treatment strategies exist to control cases of reappearing cancer. Sometimes, it is possible to use these treatments to eliminate the cancer altogether.