WHAT IS CANCER?

1. What is a neoplasm?

A neoplasm is a new growth of tissue (tumor) in which cells grow progressively under conditions that do not prompt the growth of normal cells. A malignant neoplasm (cancer) is composed of cells that invade other tissues and spread.

2. What kinds of cancers are there?

Malignant tumors of epithelial (surface tissue) cells are carcinomas. Malignant tumors of mesenchymal (connective tissue) cells are sarcomas. Carcinomas and sarcomas are solid tumors. Hematologic malignancies, such as leukemia, are liquid tumors of mesenchymal origin.

3. What about skin cancers?

Most basal cell and squamous skin cancers are life-threatening only if neglected. They occur in tremendous numbers and are seldom fatal with proper treatment. Although the general principles of cancer management apply to skin cancers, they usually are not considered in the same class with other solid tumors.

4. Why is cancer bad for you?

There is no simple answer. The replacement of normal tissue by tumor eventually causes organ dysfunction. If a tumor outgrows its blood supply and becomes necrotic, local inflammation ensues. Often obstruction (with compromise of the lumen) of the gastrointestinal tract, bile ducts, or airway develops as the tumor grows. Occasionally the cancer bleeds (but life-threatening bleeding is rare). Nerve invasion or inflammation typically cause pain, which may be excruciating. Cancers also may elaborate humoral factors (e.g., gastrin) that cause symptoms.

5. Are all cancers life-threatening?

Cancer is a fatal disease. It is uncommon for a patient with an untreated cancer to die of something else. Currently more than 50% of patients with cancer in the United States are cured.

6. How do cancers start?

No one knows, but cells begin to grow under circumstances when they should not. They stop responding to antigrowth signals, promote their own blood supplies, are seemingly able to replicate endlessly, and do not undergo programmed cell death (apoptosis).

7. Is this process the same for all cancers?

No, the order in which these changes take place seems to vary among types of cancer and even between individual tumors with the same histologic type. Occasionally, a single mutation alone causes cancer, but many genetic alterations are usually involved.

8. Do all cancers spread?

About 25% of patients with solid tumors have detectable metastases at the time of diagnosis. Fewer than 50% of the remainder develop metastases during the course of treatment. At diagnosis, a cancer is usually at least 1 cm in diameter (and often much larger), containing millions of cells. It is surprising that metastases have not occurred in all patients at the time of diagnosis.