Peritoneal disseminations from appendiceal vs. colorectal mucinous adenocarcinoma. An Italian multicentric comparative study.

BACKGROUND

We compared baseline characteristics, outcomes and patterns of failure between patients undergoing cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) for peritoneal disseminations from appendiceal (MACA) or colorectal mucinous adenocarcinoma (MCRC), in order to assess clinical and prognostical differences.

METHODS

Prospectively collected data for 402 patients treated for MACA (n = 218) or MCRC (n = 184) in 17 Italian centers were retrospectively analyzed.

RESULTS

Colorectal origin was associated with lower peritoneal cancer index (PCI) (P < 0.001), lower rates of signet-ring cells histology (P = 0.016), T4a/b primaries (P < 0.001), negative nodes (P < 0.001), synchronous metastases (P < 0.001), microsatellite stability (P = 0.009), wild-type KRAS (P < 0.001) and BRAF (P < 0.001), but not wild-type NRAS (P = 0.999), incomplete cytoreduction (P = 0.014), and perioperative systemic anticancer treatments (s-ACT) (P < 0.001). Median follow-up was 70.5 months (95% confidence interval [CI] = 45.8-92.3) for MACA, and 40.2 months (95%CI = 35.4-55.2) for MCRC. Five-year overall survival was 58.9% (95%CI = 51.3-67.5) for MACA, and 35.4% (95%CI = 27.1-46.2) for MCRC (P < 0.001). Appendiceal origin correlated with better prognosis at multivariate analysis (hazard-ratio 2.52; 95%CI = 1.50-4.25; P < 0.001). Five-year cumulative incidence of distant relapses was higher for MCRC: 42.6% (95%CI = 30.8-52.4) vs. 28.1% (95%CI = 19.7-35.7) (P = 0.032). Incidence of peritoneal relapse was not different (P = 0.706). PCI correlated with survival in MCRC (P < 0.001), but not in MACA. Perioperative s-ACT correlated with worse prognosis in MACA (P = 0.024), but not in MCRC (P = 0.920).

CONCLUSIONS

Peritoneal disseminations from MACA are associated with distinct clinical-biological features, better prognosis and lower incidence of systemic relapses, suggesting that MCRC and MACA are different entities. MACA should not be excluded from CRS/HIPEC based only on higher PCI. The role of s-ACT remain unclear.