Is oestrogen receptor-negative/progesterone receptor-positive (ER-/PR+) a real pathological entity?

Background: The existence of oestrogen receptor-negative (ER-)/progesterone receptor-positive (PR+) breast cancer continues to be an area of controversy amongst oncologists and pathologists. Methods: To re-evaluate breast cancers originally classified as ER-/PR+ via Oncotype DX (R) assay and compare molecular phenotype with Recurrence Score (R) (RS) result, clinicopathologic features and clinical outcomes were retrospectively obtained from electronic health records between January 1998 and June 2005. Archived formalin-fixed, paraffin-embedded (FFPE) tumour specimens were tested for the expression of ER, PR and human-epidermal-growth-factor-2. The number of positive ER-/PR+ samples confirmed by transcriptional analysis was the primary outcome of interest with event-free and overall survival as secondary outcomes. Biopsies from 26 patients underwent Oncotype DX testing and analysis. Results: Approximately 60% were middle-aged (40-50 years old) women, and 84.6% had invasive ductal carcinoma. Based on the Oncotype DX assay, approximately 65% (N = 17) had ER+/PR+ status; 23% (N = 6) had ER-/PR- status; and 12% had a single hormone positive receptor (1 ER-/PR+, 2 ER+/PR-) status. Almost one-quarter of patients were stratified into the low-RS (<18) or intermediate-RS (18-30) results, and half of the patients had a high-RS (>30) result. Conclusion: Our findings suggest the ER-/PR+ subtype is not a reproducible entity and emphasises the value of retesting this subtype via molecular methods for appropriate treatment selection and patient outcomes. Multigene assay analysis may serve as a second-line or confirming tool for clinical determination of ER/PR phenotype in breast cancer patients for targeted therapies.

Automated summary

This study re-evaluated ER-/PR+ breast cancer and found it to be an unstable subtype. Multigene assay analysis can help determine the phenotype of breast cancer patients, guiding the selection of targeted therapies.