Abstract Background Numerous studies have shown the efficacy of PD-L1/PD-1 based immunotherapies (IMT) for treating patients with metastatic Breast Cancer (MBC) when there is high expression of PD-L1 in their tumor cells and/or tumor immune cells. However, many patients with high PD-L1 tumors do not respond to IMT, and some patients with negative/low PD-L1 tumors may respond to IMTs. The poor correlations between IHC scores and IMT responses are often attributed to the dynamic nature of PD-L1 which may upregulate after chemotherapy, radiation, or other systemic therapies, which is not quantified by IHC tumor immunostaining. Recently, a number of clinical trials have described PD-L1 upregulation in giant phagocytic stromal macrophages found in circulation, i.e. Cancer associated macrophage-like cells (CAML), that may correlate with IMT responses in solid tumors. We conducted a prospective pilot study to monitor the peripheral blood of n=67 MBC patients undergoing systemic treatment with IMT in combination with other therapies, to evaluate CAML PD-L1 prior to and post IMT induction (∼47 days) with clinical outcome analysis at 2 years. Methods In a prospective pilot study of previously treated MBC patients n=67, all starting new lines of systemic therapy in combination with IMT (pembrolizumab n=57, nivolumab n=2, or atezolizumab n=8) with active progressive metastatic disease. Of the patients, median age was 58.2 (range: 32-73). Median prior lines of therapy in the metastatic setting was 2 (range 0-14). Race demographics (Caucasian=43, Black=7, Hispanic=4, Asian=3 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-09-25.
Adams et al. (Tue,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: