Basal subtype, as approximated by triple-negative phenotype, is associated with locoregional recurrence in a case-control study of women with 0-3 positive lymph nodes after mastectomy

Purpose: Basal subtype, as approximated by the triple-negative phenotype (ER-PR-Her2-), has correlated with higher LRR in recent studies. Indications for postmastectomy RT (PMRT) in women with 0-3 positive lymph nodes remain unclear. We evaluated the importance of biologic subtype in a cohort of women with LRR after mastectomy. Methods: We identified 22 women with 0-3 positive lymph nodes at our institution who were initially treated with mastectomy (without post-mastectomy radiation), suffered LRRs, and had paraffin-embedded tissue blocks from the primary mastectomy specimen available for staining. None of these women received PMRT. We case-control matched these to 29 women with 0-3 positive nodes who had mastectomy (no PMRT) and remained without evidence of disease at last follow-up and had available primary specimens for processing. We matched controls for age (±3 years) and follow-up duration (<5 year vs. more). Paraffin-embedded specimens were used to construct a triple-redundant tissue microarray. We used conditional logistic regressions to study the association between each predictor and LRR. Results were summarized based on odds ratio (OR). Results: On univariate analysis, ER+, PR+, or the combination was strongly associated with lower odds of LRR. Basal subtype, as approximated by ER-PR-Her2- (TN), was associated with higher LRR (OR 8.5, p = 0.048). Use of chemotherapy also was associated with lower LRR (OR 0.126, p = 0.0073). Conclusions: Our data are concordant with reports from others demonstrating that TN phenotype is associated with higher LRR and can be considered along with other predictors of LRR when selecting women for PMRT.