Irinotecan

• You may know this drug as: Campto®, Camptosar®
• Why it's commonly used: This chemotherapy drug is used to treat colorectal cancer and other cancers.
• Side effects: Severe immune system suppression and other health problems
• What you can do: Knowing your genetic risk of side effects allows you and your doctor to choose the right drugs for you, and opt for alternatives or different doses if needed.
• Did you know? About 20 to 35 percent of patients treated with irinotecan experience severe side effects.

One particular gene helps the body metabolize this cancer medication. People who don’t carry the risk-related variant of this gene have average levels of this enzyme and will break down irinotecan more quickly. People who have one or two copies of the risk variant, on the other hand, have lower levels of the enzyme and may break down the drug more slowly. Because the drug lingers longer in the systems of people with the risk variant, they are more prone to severe side effects.

It’s important to note, though, that this gene also relates to the effectiveness of irinotecan. This drug, given at standard doses, is actually likely to be more effective for people with one or two copies of the risk variant. In such cases, a complex decision may be required. Doctors and patients will probably want to weigh the risk of side effects against the potential benefits of irinotecan in a fight against cancer.