Predictors of Overall Survival among Hormone Receptor Positive Patients with Oligometastatic Breast Cancer

Abstract

It is proposed that in some patients, isolated metastatic disease may represent an oligometastatic state as opposed to the first of many inevitable metastatic lesions. Breast cancer receptor subtype surrogates are clearly associated with varied natural history. Subtype surrogate-specific data to distinguish breast cancer patients in whom apparent oligometastatic disease (OMD) is associated with the short-term development of widely metastatic cancer are limited. Furthermore, no study has explored oligometastatic outcomes in concordance with hormone receptor (HR) positivity as a non-dichotomous variable. In this cohort of patients with metastatic breast cancer and a positive HR status quantified along a range from 0-100%, we propose using improved overall survival (OS) as a surrogate for a genuine oligometastatic state in order to identify predictors of OMD and, thus, patients who may benefit from ablative radiotherapy. We reviewed 765 patients diagnosed with metastatic, hormone receptor (HR)-positive breast cancer and treated at MD Anderson Cancer Center between August 1987 and March 2012. Classification and Regression Trees (CART) analysis was used to determine survival risk groups among patient and tumor characteristics including inflammatory breast cancer, race, age at diagnosis, estrogen receptor (ER) and progesterone receptor (PR) status, HER2 status, isolated versus multiple metastasis, visceral metastasis, and performance status. Final CART node size was limited to 20 patients or greater. Once the initial tree was formed, all identified nodes were ordered by the relative hazard ratios, and an additional CART analysis was performed on the ordered nodes to combine nodes into groups with similar risk. The model divided patients into 3 risk groups (p<0.001). The low-risk group (91.7% OS at 2 years) consists of patients with good performance status, a single metastatic site, and either PR% >1 or ER% >70. The moderate-risk group (79.8% OS at 2 years) consists of 2 distinct groups: 1) Pre-menopausal patients with good performance status, a single metastatic site, and PR% ≤1, ER%≤70 or 2) Non-black patients less than 72 years of age with good performance status, multiple metastases, and ER% >10. The high-risk group includes all other patients (51.0% OS at 2 years). HER2 status and a diagnosis of inflammatory breast cancer were not found to meaningfully divide patients into risk groups. Quantitative HR profile may help identify HR-positive patients with good PS and isolated metastases who are optimal candidates for ablation in addition to systemic and traditional hormonal therapy. Validation using prospective clinical data when available from ongoing randomized trials is warranted.