The Use and Impact on Treatment Decision of the 21-Gene Recurrence Score Assay for Patients With HR+/HER2- Early Breast Cancer in Portugal: A Nationwide Retrospective Cohort Study.

[BACKGROUND] The 21-Gene Recurrence Score Assay (Oncotype DX) is a genomic test that quantifies the likelihood of distant recurrence and predicts the potential benefit from adjuvant chemotherapy in patients with hormone receptor-positive (HR+), HER2- early breast cancer. This study aimed to evaluate the use and impact of the assay on treatment decision-making in Portugal through a nationwide retrospective cohort analysis.

[METHODS] We conducted a nationwide, multicenter, retrospective cohort study of 1083 RSA tests in 1079 patients with HR+/HER2- breast cancer between 2012 and 2021, across 36 oncology centers. We analyzed Recurrence Score (RS) distribution, adjuvant chemotherapy (ACT) prescribing patterns, correlations with clinicopathologic features, and recurrence data. Predictors of RS > 25 were evaluated using multivariable analysis and the Johns Hopkins RS Estimator (JHRE).

[RESULTS] Most patients had pT1 tumors (> 60%) and luminal B-like profiles (75%) with high hormone receptor expression (median ER 100%, PR 80%). RS > 25 occurred in 14.9% of node-negative and 15.5% of node-positive cases. ACT use shifted after TAILORx publication, with decreased use in RS < 16 and increased use in RS > 25, including among patients ≤50. ACT use for intermediate RS (16-25) dropped from 62% to 30% in patients ≤50. PR and Ki-67 were independent predictors of RS > 25. The JHRE showed moderate accuracy (53.6%) and specificity (47.7%). Among patients with a predicted RS > 25 risk < 5%, only 5% had actual high scores. Recurrence was observed in 2.3% of patients (median follow-up: 29 months).

[CONCLUSION] RSA has been increasingly adopted in Portugal and influenced ACT decisions. PR and Ki-67 can help refine patient selection for RSA, particularly in resource-limited settings. Clinical trial results significantly shaped treatment patterns.