倉科 憲太郎

BACKGROUND AND PURPOSE: The peritoneal cavity constitutes a unique immune microenvironment that critically influences the pathobiology of peritoneal metastasis (PM). This study aimed to clarify the mechanisms by which local immune alterations affect the efficacy of intraperitoneal (IP) chemotherapy for PM from gastric cancer (GC). METHOD: Peritoneal lavage or ascitic fluid was obtained from 42 patients with GC and PM treated with IP paclitaxel (PTX) in combination with systemic oxaliplatin and oral S-1. Serial samples from 31 patients were analyzed after 1-3 cycles of chemotherapy. Immune cell subsets were evaluated using multicolor flow cytometry with monoclonal antibodies, and the functional properties of peritoneal eosinophils were assessed using gene expression profiling and cytotoxicity assays. RESULTS: IP chemotherapy was associated with decreased CD4(+) T cells and increased CD11b(+) myeloid cells. Notably, many patients, particularly those with negative cytology (CY0), exhibited striking recruitment of CD66b(+) CD16(-) CD193(+) Siglec-F(+) eosinophils into the peritoneal cavity. Eosinophil expansion was correlated with improved clinical outcomes. Post-treatment eosinophils displayed an activated, partially degranulated phenotype with elevated CD11b and CD63 expression and distinct messenger RNA signatures compared with circulating eosinophils. Peritoneal eosinophils demonstrated the ability to induce apoptosis in GC cells. CONCLUSION: IP PTX promotes the recruitment and activation of eosinophils with potent antitumor activity in the peritoneal cavity. Early post-treatment abdominal eosinophilia is a robust prognostic biomarker and may represent a promising therapeutic target to enhance the efficacy of IP chemotherapy in patients with PM from GC.

BACKGROUND: Patients with advanced gastric cancer (GC) with peritoneal involvement have a dismal prognosis. Recent clinical trials have shown that anti-Claudin18.2 (CLDN18.2) antibody (zolbetuximab) enhances survival in patients with GC expressing high levels of CLDN18.2. However, the effectiveness of the zolbetuximab in patients with peritoneal metastases (PMs) remains unclear. In this study, we aimed to evaluate the expression of CLDN18.2 in disseminated lesions to assess the clinical utility of zolbetuximab in the treatment of GC with PM. METHODS: In 42 patients diagnosed with stage IV GC with PM, biopsy samples from the primary tumors and peritoneal metastatic nodules were collected and immunostained using the specific antibody (43-14A, Ventana). The expression of CLDN18.2 was comparatively evaluated based on staining intensity and the proportion of positive cells. RESULTS: Positive immunoreactivity of CLDN18.2 was observed in 37 (88%) of the primary tumors. Specifically, CLDN18.2 positivity was identified in 26 (62%) or 12 (29%) patients based on moderate to strong membrane staining in at least 40% or 75% of tumor cells, respectively. In comparison, the staining intensity in tumor cells was consistently reduced in PM across all patients. CLDN18.2 expression was absent in PM of 29 (69%) patients, while 3 (7.1%) cases were determined to be CLDN18.2-positive based on a cutoff value of 40% for high staining. This trend was particularly pronounced in cases with undifferentiated type and human epidermal growth factor receptor 2 (HER-2) negative primary tumors. CONCLUSIONS: Although CLDN18.2 expression in PM mirrored that in primary lesions, the levels were generally reduced. When zolbetuximab is used for GC patients with peritoneal involvement, it is preferable to assess the expression of CLDN18.2 in the disseminated lesions.