Our recent study (1) is the largest of many of different designs aimed at investigating the relationship between Nonmelanoma skin cancer (NMSC) and subsequent primary malignancies. Our results are in line with the most comprehensive systematic review on this relationship: it reported significantly increased overall relative risks in 15 of its 21 studies (2).
It is true that we were unable to adjust for smoking, BMI (as a marker of dietary fat intake), alcohol intake and UV exposure. However, cohort studies adjusting for individual level data on smoking, alcohol, BMI, skin color, and a number of other risk factors (3, 4) also show an increased cancer risk after NMSC.
In his own meta-analysis (5), Grant adjusts for the relative risk of lung cancer as a crude proxy for smoking, despite the lack of definitive evidence linking smoking with NMSC. He states that the decreased risks he finds for four cancers after NMSC are “nearly direct evidence that solar UVB reduces the risk of many internal cancers” with, he postulates, the likely mechanism being increased production of vitamin D. There is, however, a lack of high-quality evidence showing a low risk of other cancers after NMSC. A more robust methodology than that in Grant's study, and greater consistency of results showing low cancer rates associated with NMSC, would be needed to support his claim about UBV and the risk of cancer.
The hypothesis that NMSC is a marker of increased vitamin D status, and that increased vitamin D status reduces the risk of internal malignancies, is not completely precluded by our results (1). However, if such hypothesized protective effects are real, their effects seem to be far outweighed by the increased risks associated with having an NMSC. The balance of available evidence points strongly in favor of the multiple primary cancers model, in which NMSC is associated with an increased risk of a range of other malignancies.
See the original Letter to the Editor, p. 1438
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.