Background/Objectives: Peritoneal metastases (PMs) arise from gastrointestinal, gynecologic, hepatobiliary, and colorectal origins and are associated with poor outcomes. Cytoreductive surgery (CRS) with intraperitoneal (IP) chemotherapy offers benefit for select patients, but survival remains limited. This review aims to summarize recent insights into the molecular and tumor microenvironmental (TME) changes characteristic of PMs and the impact of IP chemotherapy. Methods: A literature review was performed using recent clinical, translational, and preclinical studies examining alterations in molecular signaling, DNA repair alterations, metabolic pathways, and angiogenic factors in PMs before and after IP therapy. Results: Peritoneal metastases exhibit distinct biology after being treated with IP chemotherapy. Treatment induces alterations in gene expression, mutational patterns, and immune infiltrates. Heated intraperitoneal chemotherapy (HIPEC) has been associated with increased CD8+ T-cell activity, macrophage and NK cell shifts, and modulation of PD-1/PD-L1 signaling, which correlate with treatment response and survival. Emerging data on PIPAC similarly suggests induction of favorable gene expression changes with repeated treatment, though supporting evidence remains more limited than for HIPEC. Angiogenic pathways—particularly VEGF and HIF1α—remain key drivers of PM progression and predictors of post-operative outcomes. Early findings suggest potential synergy between IP chemotherapy and immunotherapy though clinical trials are ongoing. Conclusions: IP chemotherapy induces tumor microenvironmental changes that have potential to shape therapeutic response. Characterizing these measurable biologic changes may allow clinicians to improve patient selection and support the development of combination therapies to enhance outcomes.
Khurshid et al. (Fri,) studied this question.