<b>What is cancer?</b><br>Cancer is a group of many related diseases that begin in cells, the body's basic unit of life. The body is made up of many types of cells. Normally, cells grow and divide to produce more cells only when the body needs them. This orderly process helps keep the body healthy. Sometimes cells keep dividing when new cells are not needed. These extra cells may form a mass of tissue, called a growth or tumor. Tumors can be either benign (not cancerous) or malignant (cancerous). Cancer can begin in any organ or tissue of the body. The original tumor is called the primary cancer or primary tumor and is usually named for the part of the body in which it begins. 

<b>What is metastasis?</b><br>Metastasis means the spread of cancer. Cancer cells can break away from a primary tumor and travel through the bloodstream or lymphatic system to other parts of the body. Cancer cells may spread to lymph nodes near the primary tumor (regional lymph nodes). This is called nodal involvement, positive nodes, or regional disease. Cancer cells can also spread to other parts of the body, distant from the primary tumor. Doctors use the term metastatic disease or distant disease to describe cancer that spreads to other organs or to lymph nodes other than those near the primary tumor. When cancer cells spread and form a new tumor, the new tumor is called a secondary, or metastatic, tumor. The cancer cells that form the secondary tumor are like those in the original tumor. That means, for example, that if breast cancer spreads (metastasizes) to the lung, the secondary tumor is made up of abnormal breast cells (not abnormal lung cells). The disease in the lung is metastatic breast cancer (not lung cancer).

<b>Is it possible to have a metastasis without having a primary cancer?</b><br>No. A metastasis is a tumor that started from a cancer cell or cells in another part of the body. Sometimes, however, a primary cancer is discovered only after a metastasis causes symptoms.

<b>How does a doctor know whether a cancer is a primary or a secondary tumor?</b><br>The cells in a metastatic tumor resemble those in the primary tumor. Once the cancerous tissue is examined under a microscope to determine the cell type, a doctor can usually tell whether that type of cell is normally found in the part of the body from which the tissue sample was taken. For instance, breast cancer cells look the same whether they are found in the breast or have spread to another part of the body. So, if a tissue sample taken from a tumor in the lung contains cells that look like breast cells, the doctor determines that the lung tumor is a secondary tumor. Metastatic cancers may be found at the same time as the primary tumor, or months or years later. When a second tumor is found in a patient who has been treated for cancer in the past, it is more often a metastasis than another primary tumor.

<b>What treatments are used for metastatic cancer?</b><br>When cancer has metastasized, it may be treated with chemotherapy, radiation therapy, biological therapy, hormone therapy, surgery, or a combination of these. The choice of treatment generally depends on the type of primary cancer, the size and location of the metastasis, the patient's age and general health, and the types of treatments used previously..."
