225P - Assessment of immune cell populations in the peripheral blood of metastatic prostate cancer

Background

Prostate cancer ranges from indolent to aggressive, with 10–20% of patients developing metastases. Immune cell interactions in the tumor microenvironment facilitate growth. This study aimed to characterize circulating immune cells in patients with oligometastatic (OMPC) and plurimetastatic prostate cancer (PMPC).

Methods

This retrospective cohort study included individuals with metastatic prostate cancer (mPC). Patients were classified into two groups: OMPC (five or fewer lesions in bone and/or lymph nodes via CT or bone scans), and PMPC, those not meeting OMPC criteria. Demographic data and immune cell subsets were collected at admission. After blood collection, peripheral blood mononuclear cells were isolated, and flow cytometry assessed various immune populations (γδ T cells, αβ T cells, Tregs, memory T cells, effector T cells, NK cells, NKT cells, B cells, myeloid cells, and monocytes) and cytokines (TNF-α, IFN-γ, IL-17). The Mann–Whitney U test was used for comparisons, with p ≤ 0.05 considered significant.

Results

43 patients were identified, with a median age of 64 years (50-80). 17 patients (39.5%) had OMPC and 26 (60.5%) had PMPC. 16 patients (37.2%) presented with de novo mPC. Bone was the most common metastatic site in both groups. Most patients (67.4%, n=29) received hormone therapy (HT) as first-line treatment , while 9 patients (20.9%) received chemotherapy plus HT. An increase in γδ2+ T cells (p=0.048) was noted in the OMPC group. There was a trend toward increased levels of γδ2+ expressing IFN-γ (p=0.066) in PMPC patients.

Conclusions

A significant increase in γδ2+ T cells was observed in OMPC. These cells are critical for immune modulation. Elevated levels in OMPC subgroup may indicate an active immune response, potentially providing a protective effect against tumor progression in this subgroup. Conversely, PMPC patients showed a trend toward increased IFN-γ expression in γδ2+ T cells (p=0.066). While these cells can produce IFN-γ, those in OMPC may be less activated, limiting their effectiveness and suggesting an immune escape mechanism. This study has limitations; results are exploratory and require confirmation in a larger cohort. We plan to validate the differences in γδ2+ T cells and IFN-γ expression in an independent group.

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.