Background Coal tar is often used in dermatological therapy, although it is a recognized tumour initiator. Previous studies with observation periods of up to 25 years have not shown any increased risk of cancer in these patients, but no longer term follow up is available although the induction period for cancer is not known.
Objective To evaluate the relative risk of cancer in a group of patients who had been treated extensively with coal tar in the period 1917–1937.
Method The medical records of 117 patients treated extensively with coal tar from 1917 to 1937 were examined. Of these, a cohort of 88 patients (75%) were eligible for study. Cancers were identified through the Danish Cancer Registry, and relative risk of cancer in this cohort was calculated.
Results The overall relative risk of cancer for the treated patients was found to he 0.4 (0.2–0.8).
Conclusion No overall increased risk of cancer was apparent in this group compared to that of the general population. These data provide further support of the safety of coal tar in the management of dermatological disease.