Abstract PS3-12-26: Interplay Between Therapy-Induced Senescence and Macrophage Polarization in the Tumor Microenvironment of Triple-Negative Breast Cancer

Abstract Tumor microenvironment (TME) plays a critical role in cancer progression, with tumor-associated macrophages (TAMs) acting as key modulators of immune suppression and metastasis. Emerging evidence suggests that cellular senescence may influence the function of TAMs; however, the underlying mechanisms remain poorly understood. In this study, we investigated the interplay between therapy-induced senescence (TIS) and TAMs, focusing on the impact of senescent cancer cells on macrophage phenotype and the therapeutic modulation of TAMs using Pexidartinib (PLX3397), an inhibitor of M2-like polarization. Using the 4T1 triple-negative breast cancer cell line and RAW264.7, the established macrophage cell line, we found that conditioned media from senescent cancer cells did not induce macrophage senescence. In contrast, direct exposure of RAW cells to doxorubicin significantly induced senescence and promoted an M2-like, pro-tumorigenic phenotype characterized by elevated CD206 expression. At the molecular level, senescent macrophages showed increased expression of p53 and p21, confirming senescence induction. Moreover, a reduction in IL-6 mRNA levels supported the shift toward M2 polarization. Notably, pretreatment with PLX3397 led to a marked reduction in macrophage numbers in senescent cultures, suggesting impaired TAM survival. These findings reveal a role for senescence in promoting M2-like macrophage polarization and highlight the potential of PLX3397 as a therapeutic strategy to target senescent TAMs and reshape the immune landscape within the TME. Citation Format: H. M. As Sobeai, S. Almufadhili, S. Alhudaithi, M. Alotaibi. Interplay Between Therapy-Induced Senescence and Macrophage Polarization in the Tumor Microenvironment of Triple-Negative Breast Cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-12-26.