Abstract P1-05-25: Clinical and biological features of 158 consecutive and unselected oligometastatic breast cancers
Authors: LACAZE Jean Louis , de la Perrière Clémence Brac , Ung Mony , Dalenc Florence , Nicolai Vincent , De Maio Eleonore , Montastruc Marion , Cabarrou Bastien , Monselet Nils , Chira Ciprian , Glemarec Gauthier , Cassou-Mounat Thibaut 
Published: March 2023

Abstract
Background: In order to determine the optimal treatment strategy for oligometastatic breast cancer (OMBC), effective and safe treatments for metastatic sites and sensitive and specific imaging techniques are needed. But it is also essential to know the incidence of oligometastatic breast cancer and its clinical and biological characteristics [1]. Efficient imaging techniques and therapeutic tools exist, but knowledge of incidence, clinical and biological characteristics of OMBC is scarce. This is partly due to the lack of publications describing these data on recent, consecutive, and unselected series of OMBC. Methods: we retrospectively collected data from 998 patients diagnosed with synchronous or metachronous metastatic breast cancer (MBC) between January 2014 and December 2018 at our institution. The only criterion used to define OMBC was the presence of one to five metastases at diagnosis. Hormone receptor (HR) and HER2 receptor status, histology, SBR grade, number of metastases and organs affected were collected. Results: Of 998 MBC, 15.8% were OMBC (158/998). Among the series, 88% (139/158) of OMBC had 1 to 3 metastases and 86.7% (137/158) had only one organ involved. Among 158 patients, 52.5% (n=83) had bone metastases, 20.9% (n=33) had lymph node metastases, 14.6% (n=23) had liver metastases, 13.3% (n=21) had brain metastases, 8.2% (n=13) had lung metastases, and 3.8% (n=6) had others (skin, pancreas, adrenal). Among these 158 patients, 83.4% (n=131) had ductal breast carcinoma, 55.7% (n=88) had HR+/HER2- OMBC, 25.3% (n=40) had HER2+ OMBC and 19% (n=30) had HR-/HER2- OMBC. HR+/HER2- subtype was statistically associated with bone and bone only metastases (p=0.001), HER2+ subtype with brain metastases (p=0.001) and HR-/HER2- subtype with lymph node metastases (p=0.008). Visceral metastases (lung or liver) are not statistically associated with any biological subtypes. The proportion of OMBC with SBR grade III was statistically higher than in a series of 22,109 patients with MBC [2] (49.4% vs 35.2%; p&lt; 0.001). Conclusion: OMBC is a heterogeneous entity. OMBC incidence is certainly much higher than the commonly used values. OMBC is not an indolent disease, and each subgroup, according to its biological and anatomical characteristics, may deserve a specific management. [1] Hellman S, Weichselbaum RR. Oligometastases. J Clin Oncol Off J Am Soc Clin Oncol 1995;13:8–10. https://doi.org/10.1200/JCO.1995.13.1.8. [2] Deluche E, Antoine A, Bachelot T, Lardy-Cleaud A, Dieras V, Brain E, et al. Contemporary outcomes of metastatic breast cancer among 22,000 women from the multicentre ESME cohort 2008–2016. Eur J Cancer 2020;129:60–70. https://doi.org/10.1016/j.ejca.2020.01.016.
Citation Format: Jean Louis LACAZE, Clémence Brac de la Perrière, Mony Ung, Florence Dalenc, Vincent Nicolai, Eleonore De Maio, Marion Montastruc, Bastien Cabarrou, Nils Monselet, Ciprian Chira, Gauthier Glemarec, Thibaut Cassou-Mounat. Clinical and biological features of 158 consecutive and unselected oligometastatic breast cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-05-25.