Comparison of the Modified IHC4 Score and 21-Gene Recurrence Score Assay in Patients with Estrogen Receptor-Positive Breast Cancer

Introduction: Not only the 21-gene recurrence score (RS) assay but also online prognostic tools and immunohistochemical prognostic models predict chemotherapy benefits for women with early breast cancer. Multi-gene assays, including Oncotype DX, are expensive and not covered by insurance in some countries. Methods: In this study, we retrospectively analyzed a series of 155 patients with estrogen receptor-positive primary breast cancer for whom an Oncotype DX assay was performed between January 2016 and August 2021. The patients’ modified immunohistochemical marker (mIHC4) scores were calculated on the basis of their pathological reports. The correlations of the RS with the online tool PREDICT and mIHC4 scores were evaluated. Results: Of the patients, 43.9% were premenopausal, 147 (94.8%) had T1 or T2 tumor, and 55.5% had no positive lymph nodes. Low (0–10), intermediate (11–25), and high RSs (26–100) were obtained in 16.1%, 61.9%, and 21.9% of the patients, respectively. The RS showed no correlation with the PREDICT score (r = 0.2720) but correlated with the mIHC4 score (r = 0.6356). In addition, a stronger correlation was observed in the patients with no node involvement and in the postmenopausal patients (r = 0.6609 and r = 0.7277, respectively). Conclusions: A relatively strong correlation was observed between the RS and the mIHC4 score. The mIHC4 score is a potentially easy and useful tool to guide adjuvant chemotherapy decision making especially for postmenopausal patients with no node involvement if a genomic test could not be performed for some reason.