Cancer can be described as the growth and proliferation of abnormal cells. These cells differ from normal cells in their aggressive reproductive capabilities and their ability to starve normal cells from important resources such as blood and nutrients. Cancer is usually either benign, meaning that it is self-contained to a local area of the body, or malignant, meaning that it has the ability to spread to other bodily tissues. Malignant cancers almost always result in death if untreated, and many even when treated. The progression toward death depends on a number of factors, including the type of cancer, clinical stage of the cancer when detected, pathologic grade of the tumor, and clinical risk factors. Benign cancers aren't as problematic as malignant cancers, although they may cause symptoms and can still result in death (for example, a benign acoustic neuroma that causes high pressure in the brain). Treatment involves some combination of chemotherapy, radiotherapy, biological agents, and/or surgical resection of the tumor and possibly the surrounding tissue and organs.

As you know, cancer is usually classified by the bodily area in which it first appears. The four most deadly types of cancer in the US are lung cancer, breast cancer, prostate cancer, and colon cancer.