Long term survival in patients with bony oligometastatic breast cancer treated with curative intent: An institutional case series.

Abstract

e12574 Background: Despite recent advances in treatment, metastatic breast cancer is widely recognized as a generally incurable condition. However, oligometastatic disease remains a poorly characterized condition with few clinical trials exploring treatments and outcomes. The term itself lacks a formal definition but is often used to refer to breast cancer displaying ≤5 metastatic sites, not necessarily in the same organ. Surgical management of discrete metastases has failed to demonstrate long-term benefit, while radiotherapy for isolated bone metastases has shown promise in some retrospective studies resulting in prolonged disease-free interval. Metastatic breast tumors overexpressing HER2 represent a category where systemic therapy may offer some prolonged remission or even cure. Methods: We are conducting a retrospective review of breast cancer patients with oligometastatic disease, as defined by ≤5 sites of disease, treated at Fred Hutch Comprehensive Cancer Center (FHCC) from 2000 to 2022; we will characterize FHCC provider practices, therapies delivered, goals of treatment, and long-term outcomes. This larger ongoing effort will be reported in a separate publication. Among a cohort of patients initially identified and undergoing record review, we reviewed all patients with bone-only disease and report their outcomes here. Results: We initially identified 17 cases of oligometastatic breast cancer currently undergoing treatment at FHCC. Of these, we noted that five patients had bone-only metastases and displayed marked similarities in treatment and outcome. All presented with de novo metastatic disease, and all five had ≤2 sites of metastasis, all in the axial skeleton. Four had HER2+ tumors; of these, three were also hormone-receptor positive. The remaining patient had triple-negative disease. All were treated with curative intent, with radiation to isolated bone metastases delivered concurrently with adjuvant radiation to breast/axilla. All are living today, with a median 56 months of follow up. One remains on a systemic metastatic regimen with a CDK4/6 inhibitor, while the rest are off therapy or are completing a standard adjuvant regimen. Conclusions: Oligometastatic breast cancer represents a heterogeneous entity that may in some instances be curable, but we lack sufficient data to identify which patients may benefit from therapy with curative intent. Standard curative treatment combined with radiotherapy to isolated bone metastases produced long-term survival in five current FHCC patients, which is consistent with other reports on patients with a low burden of bone-dominant metastatic disease. Further research is needed to validate curative approaches to therapy for this understudied population.