Women with poor prognostic features of low PgR and/or high Ki-67 have greater absolute benefit from exemestane + ovarian function suppression (OFS) vs tamoxifen + OFS or tamoxifen alone, but individually PgR and Ki-67 are of limited predictive value for selecting adjuvant endocrine therapy. This according to a study of 4,115 premenopausal women with HR+/HER- breast cancer who had ER, PgR, and Ki-67 assessed by immunohistochemistry. Researchers found:

• Median ER, PgR, and Ki-67 expressions were 95%, 90%, and 18% immunostained cells, respectively.

• Lower PgR and higher Ki-67 expression were associated with reduced breast cancer-free interval.

• There was no consistent evidence of heterogeneity of the relative treatment effects according to PgR or Ki=67 expression levels; there was a greater 5-year absolute benefit of exemestane + OFS vs tamoxifen with or without OFS at lower levels of PgR and higher levels of Ki-67.

Citation: Regan MM, Pagani O, Francis PA, et al. Predictive value and clinical utility of centrally assessed ER, PgR, and Ki-67 to select adjuvant endocrine therapy for premenopausal women with hormone receptor-positive, HER2-negative early breast cancer: TEXT and SOFT trials. [Published online ahead of print October 22, 2015]. Breast Cancer Res Treat. doi: 10.1007/s10549-015-3612-z.