Doctors have determined specific combinations can be useful for specific types of cancer. Although trial-and-error is part of the process, rational choice of drugs is used to formulate combinations.

Some heuristics used to devise combinations include choosing drugs with different anti-cancer biochemical mechanisms, choosing drugs to overcome crosstalk among different metabolic pathways, choosing drugs that the body forms resistance to in different ways,  and choosing drugs with different patterns of dose-limiting toxic effects.

Related: companion diagnostics

Examples

Treatment of lung cancer often employs combination regimens. One accepted treatment for small cell lung cancer is the use of cisplatin and etoposide along with external radiation. Cisplatin and etoposide make a good team as they have different mechanisms of action and divergent toxicities.

Cisplatin disrupts cell replication by cross-linking DNA strands. While effective killers of cancer cells, platinum drugs are notorious for renal toxicity. Renal function must be monitored and patients should be well hydrated before treatment.

Etoposide irreparably damages DNA and has a side effect profile typified by bone marrow suppression. Anemic etoposide patients have low red blood cell counts and neutropenic patients have low white blood cell counts due to bone marrow suppression. Neutropenic patients are at increased risk of infection as white blood cells are infection fighters. Anemic patients are often fatigued as red blood cells are required to carry oxygen throughout the body.

Cisplatin and etoposide have synergistic killing effects on cancer and unique side effect profiles making them a powerful combination in the treatment of lung cancer. Combination therapy is not just limited to drug combinations. As the treatment of lung cancer illustrates, radiation and surgery also play a major role in cancer treatment.