Pos1150 Performance of Frax™ Risk Factors in Predicting Fracture Risk in a Cohort of Patients Treated With Aromatase Inhibitors for Breast Cancer

Background: Aromatase inhibitors decrease oestrogen production in peripheral tissues, such as adipocytes, and among other indications are used in treatment of hormone-receptor positive breast cancer in post-menopausal women [1]. However, the paradox of reduction in serum oestrogen is an alteration in bone turnover and bone density that induces a state of increased fracture risk. The gravity of the indications for aromatase inhibitors often outweigh exposure to this risk, so understanding who is more likely to develop fractures and subsequently targeting interventions to prevent them is valuable. The fracture risk assessment tool (FRAX™) is an algorithm that produces a probability of hip fracture within the next decade and could be applied for the purpose identified of highlighting at-risk patients. Objectives: Assess the association between FRAX™ risk factors and fragility fractures in an observational cohort, and if possible, identify additional risk factors. Methods: A cross-sectional analysis was conducted on data collected from 2581 female patients taking aromatase inhibitors to treat breast cancer living in Lancashire and Cumbria, UK from 2004 to 2019. Patients were offered a dual x-ray absorption scan as part of their treatment which was used to assess t-score and body fat percentage at the L1-L4 spine, and body fat percentage at the femur. Information on relating to the FRAX™ variables and whether patients had developed one or more fragility fractures was also collected. Data was analysed to obtain arithmetic means for subgroups, odds ratio and 95% confidence intervals. For discrete variables, odds ratio was calculated by exact Fisher's test. Odds ratios were determined by logistic regression for continuous variables. Results: Our study found that half of the FRAX™ risk factors were not accurate predictors of fracture risk for the patients included our cohort. Of those that were, rheumatoid arthritis and t-score were the stronger predictors. We also identified body fat percentage as measured at the femur as a strong predictor of fracture risk, resembling a similar analysis of a cohort of patients in Lombardy¹, and being congruent with the role of adipocytes in the mechanism of action of aromatase inhibitors. The small difference in the means between those with fragility fractures and those without was subject to a two-sample t test which demonstrated a statistically significant difference in means. (p= 0.0009). Conclusion: FRAX™ may not be best suited for predicting fracture risk in women on aromatase inhibitors for breast cancer. Further, body fat percentage as measured at the femur shows a strong correlation to developing fractures and should be considered in predicting fracture risk for this subset of patients. REFERENCES: [1] Pedersini R, Amoroso V, Maffezzoni F, Gallo F, Turla A, Monteverdi S, Ardine M, Ravanelli M, Vassalli L, Rodella F, Formenti AM. Association of fat body mass with vertebral fractures in postmenopausal women with early breast cancer undergoing adjuvant aromatase inhibitor therapy. JAMA Network Open. 2019 Sep 4;2(9):e1911080-. Acknowledgements: NIL. Disclosure of Interests: None declared.