Does coal tar treatment raise cancer risk?

This study followed 13,200 people treated for psoriasis or eczema in the Netherlands, comparing those who had used coal tar against those treated only with steroid creams, using national cancer registry records. Median follow-up was 21 years. Neither cancers outside the skin nor skin cancers were more common in the coal tar group. The authors concluded coal tar can be maintained as a safe treatment in dermatology. Three caveats matter for reading it fairly. Basal cell carcinoma is not recorded in the Dutch cancer registry, so the commonest skin cancer is missing from the analysis. The typical person had used coal tar for about six months, so this says little about years of heavy use. And while the skin cancer result sits squarely on no effect, the range of values compatible with the data was wide enough that a modest increase could not have been excluded. The fair summary is that no increased risk was found, not that risk has been ruled out.