Aim: Oligometastatic breast cancer (OMBC) is a disease-entity with potential for long-term remission in selected patients. Those with truly limited metastatic load (rather than occult widespread metastatic disease) may benefit from multimodality treatment including local ablative therapy of distant metastases. In this systematic review, we studied factors associated with long-term survival in patients with OMBC. Methods: Eligible studies included patients with OMBC who received a combination of local and systemic therapy as multimodal approach and reported overall survival (OS) or progression-free survival (PFS), or both. The Quality in Prognosis Studies (QUIPS) tool was used to assess the quality of each included study. Independent prognostic factors for OS and/or PFS are summarized. Results: Of 1271 screened abstracts, 317 papers were full-text screened and twenty studies were included. Eleven of twenty studies were classified as acceptable quality. Definition of OMBC varied between studies and mostly incorporated the number and/or location of metastases. The 5-year OS ranged between 30 and 79% and 5-year PFS ranged between 25 and 57%. Twelve studies evaluated prognostic factors for OS and/or PFS in multivariable models. A solitary metastasis, > 24 months interval between primary tumor and OMBC, no or limited involved axillary lymph nodes at primary diagnosis, and hormone-receptor positivity were associated with better outcome. HER2-positivity was associated with worse outcome, but only few patients received anti-HER2 therapy. Conclusions: OMBC patients with a solitary distant metastasis and > 24 months disease-free interval have the best OS and may be optimal candidates to consider a multidisciplinary approach.

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Cancer Treatment Reviews
Department of Medical Oncology

van Ommen – Nijhof, A., Steenbruggen, T.G., Schats, W., Wiersma, T, Horlings, HM, Mann, R., … Jager, A. (2020). Prognostic factors in patients with oligometastatic breast cancer – A systematic review. Cancer Treatment Reviews, 91. doi:10.1016/j.ctrv.2020.102114