Patients with Metachronous Peritoneal Metastatic Mucinous Colorectal Adenocarcinoma Benefit More from Cytoreductive Surgery (CRS) and Hyperthermic Intraperitoneal Chemotherapy (HIPEC) than Their Synchronous Counterparts

SIMPLE SUMMARY: Mucinous adenocarcinoma develops in 10–20% of all colorectal cancer (CRC) cases. This subtype is characterized by its worse clinicopathological features, including but not limited to more advanced stages at the time of tumor diagnosis, it being more frequent in the proximal colon, it showing mutation more frequently in CRC-specific protooncogenes, and its impaired response rate to various oncological treatments. Although several studies have investigated the benefits of cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS + HIPEC) in peritoneal metastatic CRC, limited data exist on the effect of mucinous CRC. Therefore, a retrospective study was conducted, and the following novel results were obtained. CRS + HIPEC is advantageous for both mucinous and non-mucinous CRC in metachronous cases, but the same cannot be said for those patients with synchronous metastases: the survival of mucinous CRC patients with synchronous peritoneal metastases was significantly worse despite the use of CRS + HPEC treatment. ABSTRACT: Background: Mucinous adenocarcinoma is a frequent subtype in colorectal cancer (CRC). A higher initial T-stage, poorer differentiation, worse response to anti-tumor therapies, and shorter survival are characteristic of mucinous CRC. Moreover, the therapeutic benefit of cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS + HIPEC) in mucinous CRC has not been significantly investigated. Methods: A retrospective analysis of 218 CRC patients with synchronous or metachronous peritoneal metastases was conducted. Results: 129 and 89 patients had synchronous and metachronous metastases, and 36 (27.8%) and 22 (24.8%) of these were mucinous CRC, respectively. Mucinous CRC was more frequent in the proximal colon, with a higher T-stage and N-stage and with an average peritoneal carcinomatosis index that was 2 values higher. Disease-specific survival was significantly worse in the synchronous mucinous group (median survival: 22.4 months vs. 36.3 months, p = 0.0229). In contrast, no such difference was observed in the metachronous cohort (32.6 months vs. 34.4 months, p = 0.6490). Conclusions: In the case of synchronous peritoneal metastases originating from mucinous CRC, the positive effect of CRS+HIPEC cannot be verified, and the added value of this highly invasive treatment is therefore somewhat questioned. However, CRS + HIPEC is recommended for metachronous metastases, since no difference between the two CRC-subtypes could be verified.