Medical researchers are constantly trying to determine which substances cause cancer. Among the substances they study are alcohol and drugs—both legal, prescription medications and illegal drugs of abuse. Another area of concern is the treatment of cancer patients who are or have been substance abusers.

Identifying Carcinogens, or Cancer-Causing Agents

There are several ways to study whether a substance is a "carcinogen," or a substance that causes cancer.

1. Cancer cells have certain abnormalities in their cell structures. Cells can be grown in a test tube to see if these cell-structure abnormalities develop.
2. The substance can be given to animals to see if cancers result.
3. Doctors and medical researchers can analyze the course of a disease in a human patient.
4. Researchers can compare the outcomes in a group of people who use a certain substance to outcomes in those who do not...