Pre‐treatment with anastrozole may be the optimal treatment sequence with radiotherapy for breast cancer

Abstract

AbstractAim: The aim of this study was to assess the in vitro effect of sequencing of irradiation and anastrozole on MCF‐7aro breast cancer cell line proliferation. Adjuvant tamoxifen therapy for breast cancer is often delayed until after completion of radiotherapy because of the potential inhibition of radiation cytotoxicity and normal tissue radiation effects. Aromatase inhibitors like anastrozole are now indicated as the first‐line adjuvant therapy for postmenopausal women, but there are little data regarding the optimum sequencing order of radiotherapy and aromatase inhibitors.Methods: Using reverse transcription polymerase chain reaction we confirmed the aromatase gene expression for MCF‐7aro cells. Comprehensive dose–response curves for MCF‐7aro were established for anastrozole and ionizing radiation (IR). Cell proliferation and colony survival were assayed for a 2 Gy fraction of IR administered either before or during incubation with 1.4 μmol/L anastrozole.Results: Compared to radiation alone, the relative day 7 cell proliferation with anastrozole exposure commenced before radiation exposure is 0.59 (95% CI 0.51–0.67) versus anastrozole exposure commenced after radiation exposure, which is 0.83 (95% CI 0.69–0.96), rank sum P = 0.007. Colony survival assays also support the possibility that pre‐radiation anastrozole treatment enhances the effects of irradiation. There was no evidence of radiation resistance as a result of pre‐radiation treatment with anastrozole.Conclusion: The initiation of anastrozole before irradiation may enhance radiosensitivity and local control for adjuvant breast irradiation.