Favorable prognostic factors of oligometastatic breast cancer: A subset analysis of OLIGO-BC1.

Abstract

1026 Background: The Federation of Asian Clinical Oncology (FACO) conducted an international retrospective cohort study of oligometastatic breast cancer (BC) (OLIGO-BC1) (UMIN No.000030047). At ASCO2020, we demonstrated that locoregional and systemic therapy prolonged overall survival (OS) for patients with oligometastatic BC, especially for cases with some type of systemic therapy, younger age, ECOG performance status 0, stage I BC, non-triple negative subtype, fewer metastatic sites, local recurrence and longer disease-free interval from a multivariate analysis (#1025). Although BC is heterogeneous and a retrospective dataset has many kinds of bias, we attempted a subset analysis based on intrinsic subtype and several prognostic factors. Methods: Oligometastatic BC patients diagnosed from 2007 to 2012 were registered from CSCO, KSMO and JSCO. OS period was measured from the diagnosis of oligometastases to the latest follow-up. ER, PgR and HER2 status were determined by immunohistochemistry and/or in situ hybridization. A hazard ratio (HR) of OS was calculated by using a univariate analysis. Results: In 1200 eligible cases, one oligometastatic site was found in 578 cases, two in 289, three in 154, four in 102 and five in 77. Bone metastases were recorded in 301 cases, visceral metastases in 387, locoregional recurrence in 25, local recurrence in 83 and multiple metastatic sites in 404. Luminal subtype was recorded in 526 cases (44%), luminal-HER2 in 189 (16%), HER2 in 154 (13%), triple-negative in 166 (14%) and others in 165 (13%). In any subtype, locoregional and systemic therapy and ECOG performance status 0 were beneficial for OS. Stage I BC, one oligometastatic site and longer disease-free interval were also related to favorable prognosis in luminal and HER2 subtype. However, triple-negative subtype had no survival advantage with these 3 factors. On the other hand, pathological negative or micrometastatic lymph nodes at primary BC and one oligometastatic site of lymph node, lung, liver and bone were favorable prognostic factors. In addition, cases treated locally with surgical resection and conventional radiation therapy were expected to prolong OS. Discussions: Locoregional therapy for oligometastatic BC may be considered in luminal and HER2 subtype with some conditions. As reported in ASCO2020, triple-negative BC should be managed with systemic therapy. Conclusions: Oligometastatic BC is diagnosed by chance, but some cases seem to survive with multidisciplinary treatment. It is worthwhile to consider locoregional therapy in oligometastatic BC after evaluating favorable prognostic factors.