Chronic Use of Hydrochlorothiazide and Risk of Skin Cancer in Caucasian Adults: A PharmLines Initiative Inception Cohort Study

Photosensitizing properties of hydrochlorothiazide may increase skin cancer risk. To date, study findings on the association between hydrochlorothiazide use and skin cancer risk are inconsistent, notably regarding confounding and dose-response. The aim of this study was to investigate the association between hydrochlorothiazide use and incidence of skin cancer in a cohort of unselected Caucasian adults, taking dosing into account. As part of the PharmLines Initiative, which links data from the Lifelines Cohort Study and prescription database IADB.nl, patients aged ≥ 40 years were included from Lifelines, a prospective population-based cohort study in the north of the Netherlands. Skin cancer incidence was compared between subjects starting hydrochlorothiazide treatment (n = 608), subjects starting treatment with other antihypertensives (n = 508), and non-antihypertensive long-term medication users (n = 1,710). Cox regression analyses were performed to obtain hazard ratios, adjusted for potential confounders. The risk of any skin cancer, keratinocyte carcinoma, basal cell carcinoma and squamous cell carcinoma was not significantly increased in general hydrochlorothiazide users. A clear association was observed between high cumulative hydrochlorothiazide use (≥ 5,000 defined daily dose; ≥ 125,000 mg) and the risk of any skin cancer (adjusted hazard ratio 5.32, 95% confidence interval (95% CI) 2.40–11.81), keratinocyte carcinoma (adjusted hazard ratio 7.31, 95% CI 3.12–17.13), basal cell carcinoma (adjusted hazard ratio 7.72, 95% CI 3.11–19.16) and squamous cell carcinoma (adjusted hazard ratio 19.63, 95% CI 3.12–123.56). These findings should lead to awareness with high use of hydrochlorothiazide in Caucasian adults. SIGNIFICANCE Hydrochlorothiazide is a widely used antihypertensive drug with photosensitizing properties, which may therefore increase skin cancer risk. However, studies are inconsistent regarding this possible association. The current study investigated skin cancer risk in hydrochlorothiazide users. This risk was compared with the skin cancer risk in subjects starting treatment with other antihypertensives and non-antihypertensive long-term medication, in order to avoid detection bias, and corrected for multiple possible confounders. A significant association with elevated adjusted hazard ratio’s in Cox regression analysis was found for patients with high cumulative hydrochlorothiazide use and risk of any skin cancer, keratinocyte carcinoma, basal cell carcinoma and squamous cell carcinoma, suggesting that providing extra information on skin cancer and its prevention is important for this group.