Proton pump inhibitor use and risk of breast cancer, prostate cancer, and malignant melanoma: An Icelandic population-based case-control study.

Purpose: Increased expression of Vacuolar-type H+ ATPases (V-ATPases), in the plasma membrane of cancer cells has been suggested to contribute to the development of aggressive cancer phenotypes by promoting acidic tumor microenvironments. Accumulating data suggest that proton pump inhibitors (PPIs) may elicit a chemopreventive effect via V-ATPase inhibition in some cancers, but evidence is still limited. Therefore, we aimed to explore a potential preventive role of PPIs in this study. Methods: In this population-based case-control study, we identified incident cases of breast cancer (n=1739), prostate cancer (n=1897), and malignant melanoma (n=385) in Iceland between 2005 and 2014 from the Icelandic Cancer Registry. We assessed varying levels of PPI use through record linkages to the Icelandic Medicines Registry. For each case, we selected up to 10 age-matched, sex-matched, and calendar-matched population controls using risk-set sampling. Using conditional logistic regression, we calculated odds ratios (ORs) and 95% confidence intervals (CIs) controlling for NSAID use. Results: Adjusted ORs associated with ever use of PPIs were 1.03 (95% CI: 0.92-1.16) for breast cancer, 1.12 (95% CI: 1.00-1.25) for prostate cancer, and 0.84 (95% CI: 0.69-1.12) for malignant melanoma. Analyses of high use of PPIs (>= 1000 DDDs) yielded ORs of 0.97 (95% CI: 0.78-1.19), 1.20 (0.99-1.47), and 0.59 (0.40-1.13) for breast cancer, prostate cancer, and malignant melanoma, respectively. Analyses of cumulative exposure to PPIs did not support a dose-response relationship for any of the three cancer types. Conclusions: Our findings do not support a chemopreventive effect of PPI use on breast cancer, prostate cancer, or malignant melanoma.