Recurrence score prediction formula based on immunohistochemistry and biopsy data to predict response to neoadjuvant chemotherapy in estrogen receptor-positive/human epidermal growth factor receptor 2-negative breast cancer: A retrospective cohort study.

Oncotype DX® is a validated 21-gene tool for assessing survival benefits of adjuvant chemotherapy for estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer, but its use in core biopsy specimens is limited by costs, access issues, and available tissue volumes, highlighting the need for an alternative to Oncotype DX®. Therefore, we developed a recurrence score (RS) prediction formula and investigated whether the RS-predicted value calculated from biopsy material could predict pathological complete responses (pCRs) from neoadjuvant chemotherapy (NAC). This retrospective cohort study examined consecutive patients with ER+/HER2- primary breast cancer who underwent surgery after NAC at Kitasato Institute Hospital between 2012 and 2023. These values were matched with histological responses to chemotherapy and other clinical and pathological factors. Among 61 patients (median age 54 years), 50% had clinical tumor status 2 tumors, and 40% had node-positive disease. Six patients (9.8%) achieved pCRs, whereas 55 (90.2%) did not. The median RS-predicted value was significantly higher in the pCR group (38.6) than in the non-pCR group (14.0). The pCR rates were 3.8% (2/53 cases) for RS-predicted values < 26 and 50.0% (4/8 cases) for RS-predicted values ≥ 26. The optimal RS-predicted cutoff value for predicting pCRs was 33.785, with a sensitivity of 66.7% and a specificity of 98.2%. Higher RS-predicted values calculated from routinely available biopsy biomarkers were associated with a greater likelihood of pCR after NAC in patients with ER+/HER2- breast cancer. These preliminary findings suggest that the RS-predicted value may have potential as an accessible tool for predicting the chemotherapy response; however, validation in larger independent cohorts and direct comparisons with the actual Oncotype DX® RS are warranted.