Histologic Predictors of Recurrence in Mucinous Appendiceal Tumors with Peritoneal Dissemination after HIPEC.

BACKGROUND: Mucinous appendiceal tumors (MAT) are rare neoplasms that can metastasize to the peritoneum and often are treated with cytoreductive surgery (CRS) and HIPEC. Pathologic classification and outcomes vary, but standardized histologic definitions are emerging. We sought to evaluate outcomes in this disease after CRS/HIPEC using standardized pathologic criteria.

METHOD: Outcomes of MAT with peritoneal metastases (PM) after CRS/HIPEC from 2007 to 2015 were reviewed at our institution. Standardized histologic categories per WHO and consensus definitions were used: low-grade appendiceal mucinous neoplasm (LAMN), low-grade adenocarcinoma (LGAC), or high-grade adenocarcinoma (HGAC) primary tumors; and acellular mucin (AM), low-grade mucinous carcinoma peritonei (LGMCP), or high-grade mucinous carcinoma peritonei (HGMCP) peritoneal metastases. Cox proportional hazards model was used identify predictors of progression-free survival (PFS) by univariate and multivariate analyses.

RESULTS: A total of 183 patients undergoing 197 CRS/HIPECs were included. Among 75 patients with primary histology review, there were 33 (44.0%) LAMNs, 28 (37.3%) LGACs, and 14 (18.7%) HGACs. Peritoneal histology was benign in 6 (3.0%), AM in 33 (16.8%), LGMCP in 114 (57.9%), and HGMCP in 44 (22.3%). PFS was not reached for AM, 34.3 months for LGMCP, and 16.8 months for HGMCP (p < 0.001). Peritoneal histology predicted PFS on multivariate analysis (hazard ratio 9.82 and 24.60 for LGMCP and HGMCP, respectively, vs. AM, p < 0.001). Among the LGMCP group, CEA and completeness of cytoreduction (CC score) predicted PFS on multivariate analysis.

CONCLUSIONS: Standardized peritoneal histology in patients with PM from MAT predicts PFS and patients with low-grade histology can be further discriminated by CEA and CC score.