CANCER RISK IN USERS OF CALCIUM-CHANNEL BLOCKERS

Ca2+ channel blockers may cause cancer by inhibiting apoptosis or redu cing intracellular Ca2+ in certain tissues. Recent findings suggest th at drug users are at increased risk for cancer in general and for colo n cancer in particular. We conducted a study in one Danish county of 1 7 911 patients who received at least one prescription of Ca2+ channel blockers between 1 January 1991 and 31 December 1993. The patients wer e identified from records in the National Health Insurance Program, wh ich refunds part of the price of such drugs. Cancer occurrence and rat e were determined by use of the files of the Danish Cancer Registry an d compared with county-specific incidence rates for various categories of cancer. During the follow-up period of up to 3 years, 412 cancers were observed among users of Ca2+ channel blockers, compared with 414 expected, to yield an age- and sex-standardized incidence ratio (SIR) of 1.00 (95% confidence interval, 0.90 to 1.10). There was no indicati on of an excess risk in the subgroup of likely long-term users or user s of specific drugs. The SIR of colon cancer, a site of a priori inter est, was 0.8 (95% confidence interval, 0.5 to 1.1) on the basis of 34 cases. Although the results are reassuring, the lack of association co uld reflect the relatively short follow-up after registration in the p rescription database. Continued monitoring of cancer risk is planned.