Response to neoadjuvant chemotherapy and the 21-gene Breast Recurrence Score test in young women with estrogen receptor-positive early breast cancer

Purpose The 21-gene Breast Recurrence Score test predicts benefit from adjuvant chemotherapy in estrogen receptor-positive, HER2-negative (ER+/HER2-) breast cancer (BC). We examined whether the 21-gene assay predicts response to neoadjuvant chemotherapy (NCT). Methods We identified patients with stage I-III ER+/HER2- BC treated with NCT from the Young Women's Breast Cancer Study, a prospective cohort of women diagnosed with BC at age <= 40 years. The 21-gene assay was performed on tumor specimens removed prior to NCT either as part of clinical care or retrospectively for research. Pathological complete response (pCR) was defined as ypT0/is ypN0. The relationship between Recurrence Score result and pCR was evaluated using logistic regression modeling. Results 76 women received NCT for ER+/HER2- BC and were eligible for this analysis. Median age at diagnosis was 37 years (range 24-40). Scores ranged between 5 and 77 with 50% >25 and 5% <11. Median Recurrence Score result was significantly higher among tumors achieving pCR vs. non-pCR response (61.5 vs. 23, p(wilcoxon) = 0.0005). pCR rate in patients with scores >25 was 21% (8/38) vs. 5% in patients with scores 25 (2/38) (p = 0.09), with both pCRs in the 25 group in patients with scores between 21 and 25. In multivariable analysis, only Recurrence Score result was significantly associated with pCR (OR: 1.07, 95%CI 1.01-1.12, p = 0.01). Conclusions In young women with ER+/HER2- BC who received NCT, higher pretreatment Recurrence Score result was associated with an increased likelihood of pCR. Gene expression profile assays may have a role in decision making in young women in need of neoadjuvant therapy.