Association between cyclooxygenase-2 expression in atypical hyperplasia and risk of breast cancer

Background The cyclooxygenase-2 (COX-2) enzyme, which is induced by inflammatory and mitogenic stimuli, plays a protumorigenic role in several human cancers. COX-2 is overexpressed in invasive and in situ breast cancers. Atypical hyperplasia in breast tissue, although benign, is associated with a high risk of breast cancer. We investigated whether COX-2 overexpression in atypical hyperplasia is associated with the risk of subsequent breast cancer. Methods COX-2 expression was assessed immunohistochemically in archival sections from 235 women with atypia whose biopsy specimens were obtained at the Mayo Clinic from January 1, 1967, through December 31, 1991. COX-2 expression was scored as 0 (negative), 1+ (weak), 2+ (moderate), or 3+ (strong). Risk factor information and follow-up for breast cancer events were obtained via a study questionnaire and the medical records. All statistical tests were two-sided. Results Forty-one (17%) of the 235 women developed breast cancer during a median follow-up of 15 years. Moderate (category 2+) or strong (category 3+) COX-2 expression was identified in 71 (30%) and 34 (14%) of the 235 samples, respectively. The risk for developing breast cancer, relative to a control population (the Iowa Surveillance, Epidemiology, and End Results registry), increased with increasing COX-2 expression (relative risk [RR] = 2.63, 95% confidence interval [Cl] = 1.56 to 4.15, for those with negative or weak COX-2 expression; RR = 3.56, 95% Cl = 1.94 to 5.97, for those with moderate expression; and RR = 5.66, 95% Cl = 2.59 to 10.75, for those with strong expression; P =.07). Overexpression of COX-2 was statistically significantly associated with the type of atypia (lobular vs ductal, P <.001), number of foci of atypia in the biopsy (P =.02), and older age at time of biopsy (>45 years, P =.01). Conclusions COX-2 appears to be a biomarker that further stratifies breast cancer risk among women with atypia and may be a relevant target for chemoprevention strategies.