The science of cancer can be complicated and confusing. To provide some clarity about a topic that will impact most of us, David Cohn, MD, the chief medical officer of The James and a gynecologic cancer specialist, provides some easy-to-understand answers to basic, but important, cancer questions. What is cancer? Think of cancer as changes in cells that cause them to grow. The continued abnormal growth of these cells can spread and cause harm to patients. How does the growth of these abnormal cells harm the body? There are several ways, including the replacement of normal, healthy cells. The classic example is within the bone marrow, as the cancer cells replace and force out the normal cells. Another way is the actual mass of the cancer cells &mdash; the tumor &mdash; that can press against organs and, as an example, cause blockage of the intestines and other parts of the body. What do cancer cells look like? Are they different from regular cells? They do look different. One of the things I look for are a lump or group of cells growing in places where they shouldn&rsquo;t be growing. And, because cancer cells and tumors tend to have a lot of extra blood vessels, they&rsquo;re often redder than normal cells. These extra blood vessels help cancer cells grow faster than normal cells. What are the most common forms of cancer? There will be about 1.7 million people in the United States diagnosed this year with cancer, and unfortunately, about 600,000 people will die. The most frequently diagnosed types are breast cancer, with about 270,000 cases, lung cancer, with about 230,000 diagnoses and prostate cancer, with approximately 175,000 cases. Next comes colorectal cancer, with 150,000 cases, followed by melanoma, with 100,000 diagnoses. What is chemotherapy? Think of chemotherapy as a type of treatment that, when given either orally with a pill or through the blood with an IV, has an impact throughout the body. We know that cancer cells grow faster than normal cells and chemotherapy targets the fast-growing cells throughout the body. Some of the body&rsquo;s faster-growing cells, such as hair follicles and the inside of the gastrointestinal tract, can also be damaged by chemotherapy, which is why patients can lose their hair and become nauseated. Are targeted and precision cancer treatments the same thing? How are they different than chemotherapy? I put precision and targeted therapies in the same category. While chemotherapy targets fast-growing cells throughout the body, targeted and precision drugs are intended to target the cancer cells specifically and spare the normal cells. Cancer cells have specific genetic mutations, and these targeted and precision treatments identify and go after these changes. Some targeted and precision treatments can be antibodies that block the increased growth of the blood vessels in tumors. How does immunotherapy work? Immunotherapy activates the body&rsquo;s immune system. Everyone has an immune system that recognizes abnormal cells, such as viruses, and that revs up to fight them. However, cancer cells are able to hide from the immune system. Immunotherapy can make these abnormal cancer cells visible to the immune system so it can better detect and kill them. This is an incredibly exciting way to treat patients, and we&rsquo;re seeing patients who historically had very bad outcomes now have incredible outcomes.