Risk of breast cancer was not statistically significantly associated with overall COX2 inhibitor use, but there was a significant trend with duration of use (Ptrend=0.002) with an increased risk in long-term users (OR 1.24, 95% CI 1.08–1.42, P=0.003), which stayed increased after stopping COX2 inhibitors more than 2 years before the index date (OR 1.23, 95% CI 1.05–1.44, P=0.009). This evidence concerns the gene PTGS2 and breast carcinoma.