Abstract P6-08-14: Bone mineral density change on aromatase inhibitors as a predictor of breast cancer recurrence

Abstract

Abstract Background Aromatase inhibitors (AIs) reduce the risk of breast cancer recurrence in hormone receptor positive breast cancers by blocking the production of estrogen. Low estrogen states are also associated with reduction of bone mineral density. AIs have been shown to lead to reduction in bone mineral density although the degree of change in bone mineral density varies between individuals. In this study we investigate the association between change in bone mineral density and recurrence in patients treated with AIs. Methods This was a retrospective cohort study utilizing a single centre breast unit database. 327 patients were identified who had an initial bone density T score result at time of commencement of AI and a subsequent result after commencement of AI treatment. There were 145 patients who had the bone density raw score available in g/cm2. Logistic regression (Stata 9) was used to predict recurrence. Two pathological prognostic factors, tumor size and number of lymph nodes, were shown to predict recurrence in this data set and were therefore used in multivariate testing. Baseline and sequential data on lumbar spine and hip T score and bone mineral density (BMD) in the same patient were analyzed for predicting recurrence and hazard of failure using a Cox model. Bone density in the models was adjusted to show either an alteration of T score of 1.0 or in BMD of 0.01g/cm2. Results The mean lumbar T score difference was a reduction of 0.26 in sequential measurements (95% CI 0.2 to 0.31). No baseline T score or BMD showed any significance in predicting recurrence or the hazard of recurrence. Logistic regression modeling showed a reduction in lumbar spine T score following commencement of AI of 1.0 would decrease the odds of recurrence by 0.28 (95%CI 0.1 to 0.75). A 0.01g/cm2 decrease in lumbar BMD would decrease the risk of recurrence by 0.79 (95% CI 0.68 to 0.94). Hip T score if decreased by a 1.0 would decrease the odds of recurrence by 0.27 (95% CI 0.08 to 0.86) and a 0.01g/cm2 decrease in hip BMD would decrease the odds of recurrence by 0.81 (95% CI 0.66 to 0.99). The hazard for recurrence from commencement of AI was also significant in the lumbar spine data for a decrease of 1.0 in the second T scores (HR 0.2 p 0.002) and for the lumbar BMD reduction of 0.01g/cm2 (HR 0.78 p<0.0001). The hip T scores and BMD did not reach statistical significance for predicting the hazard for recurrence. Conclusion Our data supports the hypothesis that reduction in bone density post commencement of aromatase inhibitor therapy is associated with reduced recurrence of breast cancer. It is likely that this association is the result of the effect of low circulating estrogen, resulting both in reduced risk of recurrence and lower bone density. This effect on bone density may prove a useful surrogate to measure efficacy of aromatase blockade and consequent anticancer effect on residual breast cancer. Citation Format: Hilary L Martin, John A Davidson, Francis Yap, Kim Chung, Muhammad A Khattak, Andrew D Redfern. Bone mineral density change on aromatase inhibitors as a predictor of breast cancer recurrence [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-08-14.