High estrogen receptor expression in early breast cancer: chemotherapy needed to improve RFS?

One of the most controversial questions in early breast cancer treatment is the need of chemotherapy in patients with estrogen receptor positive disease. Therefore, we analyzed a group of patients with high estrogen receptor (ER) expression to scrutinize the role of chemotherapy in this situation. To gauge the effect of chemotherapy on recurrence free survival (RFS) three treatment modalities were compared: endocrine treatment only, chemoendocrine treatment, and chemotherapy. 3,971 breast cancer patients whose treatment modalities as well as ER level were known, were included in this retrospective analysis. Their level of ER expression was documented as immunoreactive score (IRS). A high ER group was defined as ER IRS C9; primary endpoint was RFS. RFS was associated with ER, with the best outcome for strong and the worst result for negative expression. Adjusted to Nottingham prognostic index (NPI), RFS did not differ between the treatment cohorts of endocrine treatment and chemoendocrine treatment (P = 0.828) in the high ER group. Patients with chemotherapy alone fared significantly worse (P = 0.003). Even in high risk patients (according to NPI) the chemoendocrine and the endocrine treatment only groups did not differ significantly (HR = 1.15; 95% CI (0.56–2.34), P = 0.709). Omission of endocrine treatment led to significantly worse outcome (P = 0.013). In conclusion, RFS was significantly longer in patients with high ER expression than with weak or no ER expression. In the high expression group, there was no significant difference in RFS between endocrine treatment only and chemoendocrine therapy— even in high risk patients, for whom chemoendocrine treatment is routinely indicated. It seems insufficient for high ER patients to only consider tumor size, nodal status, and grading in order to decide which patient will benefit from adding chemotherapy to endocrine treatment.