Association of intratumoral CD68(+)CD163(+) M2-like macrophages with survival in metastatic colorectal cancer treated with chemotherapy plus bevacizumab.

Metastatic colorectal cancer (mCRC) is a common and highly lethal gastrointestinal malignancy. Although chemotherapy combined with bevacizumab is a standard first-line treatment, post-treatment resistance severely limits patients' long-term survival. While the remodeling of tumor-associated macrophages (TAMs) is closely related to targeted therapy resistance, the specific impact of TAMs and their programmed death-ligand 1 (PD-L1) expression on post-treatment resistance and prognosis remains unclear.

This study aimed to investigate the spatial distribution and immunophenotypic characteristics of CD68+CD163+ M2-like TAMs and their association with post-treatment resistance and survival. We retrospectively analyzed clinical data and tumor tissues from 44 patients with mCRC who received first-line chemotherapy plus bevacizumab and were categorized into resistant and non-resistant groups. Multiplex immunofluorescence and digital image-based quantitative analysis were used to evaluate macrophage markers (CD68 and CD163) and PD-L1 expression in the whole tumor section, tumor areas, and stromal areas. Compared with the non-resistant group, resistant patients showed significantly increased proportions and densities of CD68+CD163+ M2-like TAMs and CD68+CD163+PD-L1+ M2-like TAMs in the tumor areas (all p < 0.05).

The infiltration levels of these macrophage subsets were significantly associated with post-treatment resistance, but not with conventional clinicopathological features such as sex, age, or tumor stage. Survival analysis showed that a high density of intratumoral CD68+CD163+ M2-like TAMs was significantly associated with shorter overall survival (OS) (p < 0.05) and showed a trend toward shorter progression-free survival (PFS) (p = 0.06). Multivariate Cox regression further demonstrated that dense intratumoral infiltration of CD68+CD163+ M2-like TAMs was independently associated with unfavorable OS and PFS. In mCRC patients exhibiting resistance to chemotherapy combined with bevacizumab, the infiltration of intratumoral CD68+CD163+ M2-like TAMs and their PD-L1-expressing subsets is significantly elevated.

Notably, a high density of intratumoral CD68+CD163+ M2-like TAMs serves as an independent poor prognostic marker for both PFS and OS.

These findings demonstrate that the spatial enrichment of CD68+CD163+ M2-like TAMs within the tumor microenvironment is closely associated with treatment resistance, suggesting that macrophage-targeted interventions may represent a potential strategy to enhance the efficacy of anti-tumor therapies in mCRC.