A new analysis from Kaiser Permanente that shows increased breast cancer risk in women who used several common pharmaceuticals. Click here for abstract.

Kaiser conducted this analysis to follow up Silent Spring Institute research that identified 47 pharmaceuticals that caused mammary gland tumors in animal studies.

The Kaiser study estimated breast cancer risk for 8 of them. The analysis was conducted in two different cohorts – women prescribed the drugs between 1969 and 1973 and women who took them in 1994 and 2006.

Furosemide, a diuretic; griseofulvin, an anti-fungal; and metronidazole, an antibiotic; were associated with small (7% to 66%) but statistically significant increases in breast cancer risk in one or both cohorts. Results for indomethacin, an anti-inflammatory; and nitrofurantoin, used to treat urinary tract infection, showed small non-significant increased risks or no increased risk. The three remaining drugs evaluated were infrequently prescribed, so analyses were inconclusive.

Kaiser Permanente is a large health care delivery system that provides services to about 30% of the San Francisco Bay area and Central Valley in California.

These findings warrant further consideration of risks and benefits of these drugs and support the relevance of the animal cancer bioassay for identifying potential human breast carcinogens. We are delighted to see colleagues using the mammary carcinogens database to generate and test hypotheses that could inform medical practice and breast cancer risk reduction.