Abstract
Regarding cimetidine, the lack of effect reflected in the 10-year postmarketing survey, other than an excess of colorectal carcinoma in the first year of treatment (which we would attribute to diagnostic difficulty), certainly does not affect our observations. The effect we have described might well be expected to improve the prognoses of patients with established colorectal carcinoma, but this is an entirely different issue from whether cimetidine would affect the incidence of colorectal carcinoma. Similarly, the case-control study cited by Tavani et al. did not describe any effect of cimetidine on the outcome of colon carcinoma. If cimetidine does produce increased tumor-infiltrating lymphocytes in colorectal carcinoma, we believe this would be very likely to improve prognosis, but we cannot see that it would be likely to affect the incidence of this disease. What is really needed is a study of a large number of patients with colorectal carcinoma who did receive cimetidine and a large number who did not. The case-control study simply does not address this issue. David L. Morris*, Warwick J. Adams
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