Dermatological exposure to coal tar and bladder cancer risk: a case-control study

Coal tar ointments are used as treatment of various skin diseases, especially psoriasis and eczema. These ointments contain several carcinogenic polycyclic aromatic hydrocarbons. Metabolites of these polycyclic aromatic hydrocarbons are excreted in the urine and therefore, dermatological use of coal tar may be associated with an increased risk of bladder cancer. The objective of this study was to evaluate the association between dermatological use of coal tar ointments and bladder cancer.

A population-based case-control study was conducted including 1,387 cases diagnosed with bladder cancer and 5,182 population controls. Information on the use of coal tar, history of skin disease, and known risk factors for bladder cancer was obtained through postal questionnaires. Logistic regression analyses were performed to estimate the risk of bladder cancer after coal tar treatment, adjusted for age, gender, smoking status, duration of smoking, and intensity of smoking.

The use of coal tar ointments was approximately equal among cases and controls (3.8% vs. 3.0%, respectively). Dermatological application of coal tar was not significantly associated with bladder cancer (adjusted odds ratio = 1.37, 95% CI: 0.93-2.01). An inverse association between bladder cancer and a history of skin disease was observed (adjusted odds ratio = 0.74, 95% CI: 0.61-0.90).

This is the first study with a specific aim to study the association between the use of coal tar preparations and bladder cancer. The results suggest that there is no reason for safety concerns with respect to the risk of bladder cancer after the use of coal tar preparations in dermatological practice.