St. Gallen endocrine response classes predict recurrence rates over time

Background: In 2007 the St. Gallen consensus panel defined three endocrine response classes: highly endocrine responsive (ER-H), incomplete endocrine responsive (ER-I) and non-endocrine responsive tumours (ER-N). However, it is uncertain whether ER-I tumours are less responsive than ER-H tumours. We investigated whether recurrence rates vary over time between response classes. Additionally, we investigated the most predictive response class definition for tamoxifen benefit. Patients and methods: We recollected tumours from 646 patients who participated in a randomized trial of adjuvant tamoxifen vs. observation. Estrogen receptor (ER), progesterone receptor (PgR), HER2 status and tumour grade were revised centrally. St. Gallen classes were evaluated for recurrence free interval (RFI). Change in hazards over time was assessed. Subsequently, 6 alternative response class definitions were compared to optimize the cut-offfor PgR and ER. Results: Schoenfeld residuals indicate a failure of proportional hazards between the endocrine response groups (p = 0.0001). The HR for recurrence risk shifted over time with the ER-H group initially being at lower risk (HR ER-H vs. ER-I 0.5), but after six years the recurrence risk increased (HR 1.9). The cut-offvalues for ER and PgR that statistically best discriminated RFI in the first 4 years for lymph node positive patients were ER ≥ 50% and PgR ≥ 75%. Conclusion: We demonstrated a marked variability in endocrine therapy benefit. Patients with ER-H tumours have a larger benefit during adjuvant tamoxifen and in the first years after accomplishing of the therapy, but suffer from late recurrences. This might have implications for optimal treatment duration.