Chemotherapy and biotherapy are both used to destroy cancer cells. So how are they different, and how are they similar?
Traditional chemotherapy uses chemical substances to treat cancer. Biological therapy, by contrast, uses living organisms, substances derived from organisms, or laboratory-made versions of those substances to act against cancer cells.
Most chemotherapy drugs – formally known as cytotoxic (cell-killing) agents – work by destroying cancer cells directly, often by damaging their DNA and causing them switch on their programmed death process, apoptosis. Because many of these drugs can also damage normal cells, they often produce side effects such as nausea, fatigue, and hair loss, or other complications, depending on the specific agents used.
Chemotherapy drugs are often used to kill cancer cells that are dispersed throughout the body or have spread to multiple sites. They may also be used to shrink a tumor before surgery or radiation treatment, destroy cancer cells that remain after surgery or radiation therapy, or help radiation and biological therapies work better.
Biological therapies (biotherapies, for short) may either attack tumor cells directly or, by stimulating the immune system, target them indirectly.
The side effects of biological therapies can vary widely, both in type and intensity. Pain, swelling, soreness, redness, itchiness, and rash at the site of infusion or injection are fairly common, but other side effects can be more severe.
The first expressly biological therapy to be approved by the U.S. Food and Drug Administration was bacillus Calmette-Guérin (BCG) therapy, which involves a weakened form of a live tuberculosis bacterium that doesn’t cause disease in humans. It was first used as a vaccine against tuberculosis, but scientists later found that when inserted directly into the bladder, it stimulates a broad immune response not only against the foreign bacterium but against bladder cancer cells as well. Approximately 70 percent of patients with early-stage bladder cancer experience a remission after BCG therapy. It is currently being studied for the treatment of additional types of cancer.
Other examples of biotherapies include: monoclonal antibodies, laboratory-produced versions of natural proteins that bind to specific surface proteins, called antigens, on cancer cells and spark an immune system response against these cells; interferon, an enzyme that bolsters the immune response to cancer cells by activating certain white blood cells; CAR T cells, which are immune system cells retrofitted with genes that can enhance their cancer-seeking and -killing ability; and vaccines that contain cancer-associated antigens to intensify the immune system’s response to a patient’s tumor cells.
An experimental biotherapy known as oncolytic virus therapy uses specific kinds of viruses that infect both cancerous and normal cells but do no damage to normal cells. In cancer cells, by contrast, they readily reproduce and ultimately cause the cells to die. Some viruses are naturally oncolytic – that is, destructive to cancer cells – while others can be modified to have oncolytic features. One of the challenges to using viruses is that they may be destroyed by the patient’s immune system before they have a chance to attack the cancer. Although no oncolytic virus has been approved for use in the United States, several such viruses are currently being tested in clinical trials.
Another experimental biotherapy for cancer is adoptive T-cell transfer, which seeks to boost the natural cancer-fighting ability of a patient’s immune system T cells. One approach is to remove T cells that have invaded a patient’s tumor, identify those with the greatest antitumor activity, grow them in a laboratory, and reinfuse them into the patient.