Cigarette smokers being treated with irinotecan (Camptosar) had a significantly reduced concentration of the drug in their blood than non-smokers.
In the body, irinotecan is converted to SN-38 which active in treating colorectal cancer. However, smokers had 40 percent less SN-38, and it was converted more quickly to a non-active state.
Possibly as a result of lower amounts of active drug, smokers had less toxicity during treatment. In particular, only 6 percent of those in the study had severe reduction in white blood cells compared to 38 percent of non-smokers. While they had somewhat less serious diarrhea, it was not significant.
Jessica M. van der Bol headed a team in the Netherlands, Sweden, and the United States who evaluated irinotecan activity and side effects in 49 smokers and 141 non-smokers who were receiving cancer treatment.
This study indicates that smoking significantly lowers both the exposure to irinotecan and treatment-induced neutropenia, indicating a potential risk of treatment failure. The data suggest that additional investigation is warranted to determine whether smokers are at increased risk for treatment failure.
In an accompanying editorial, Neal L. Benowitz from the Division of Clinical Pharmacology at San Francisco General Hospital Medical Center suggests that smokers may need to be treated with increased doses of irinotecan. He also urges that doctors encourage smokers to quit reminding them that smokers with cancer have
- Decreased overall survival
- Decreased response to radiation treatment
- An increased risk of second primary cancers
- An increased risk of infections, including pulmonary infection
SOURCE: Jessica M. van der Bol et. al., Journal of Clinical Oncology, Volume 25, Number 19, July 1, 2007, published early online June 11, 2007.
Editorial by Neal L. Benowitz in the same issue.
What this means for patients
Smokers may have a reduced response to irinotecan and should discuss this with their doctors before beginning treatment. Your doctor may want to increase the dose of irinotecan to compensate.
Smoking remains dangerous even after a diagnosis of cancer. Trying to quit may improve your chances for a better outcome.