Biological profile of oestrogen receptor alpha positive (ERalpha+) primary breast cancers in the elderly and their response to primary endocrine therapy

e20622 Background: Aromatase inhibitors (AIs) have been shown to be superior to tamoxifen in several settings. However, it is unclear whether this superiority extends to its use as primary endocrine therapy in elderly patients with early operable primary breast cancer. Biological characteristics of the tumours may aid in selecting the most suitable agent. Methods: Primary endocrine therapy with one of the AIs (anastrozole) in 64 women >70 years with ERα+ breast cancer was compared to that in 84 treated with tamoxifen during the same period. Their selection was entirely based on contraindications e.g. thromboembolic risks. Needle core biopsies were assessed, by immunohistochemistry, for expression of biomarkers as described below. Results: There was no significant difference between the two groups (anastrozole vs tamoxifen) in terms of response at 6 months (clinical benefit (objective response + stable disease) rates = 97 vs 100%, p=0.099) or progression free survival (median = 16.5 vs 22.5 months, p=0.376). There were no withdrawals due to side effects from anastrozole, compared to four with tamoxifen. For all patients progesterone receptor (PgR), ERβ2, human epidermal growth factor receptor 2 (HER2), epidermal growth factor receptor (EGFR) and Ki-67 were over-expressed in 48%, 99%, 8%, 4% and 64% respectively. HER2 (18 vs 21 months, p=0.003) and Ki-67 (17.5 vs 23 months, p=0.042) over-expression were significantly associated with shorter progression free survival. Conclusions: These results thus far show that primary endocrine therapy with anastrozole in elderly patients with early operable ERα+ breast cancer is similar to tamoxifen in terms of efficacy, but may be better tolerated. In this population, ERα+ breast cancer also appears to have a less aggressive biological profile favouring better hormone sensitivity. [Table: see text]