Ki67 Does Not Predict Recurrence for Low Grade Appendiceal Mucinous Neoplasms with Peritoneal Dissemination after Cytoreductive Surgery and HIPEC.

Abstract Introduction Low-grade appendiceal mucinous neoplasms can disseminate to become low-grade mucinous carcinoma peritonei (LGMCP), which is optimally treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC). Approximately half of patients with LGMCP recur despite complete cytoreduction, and risk factors for recurrence are poorly understood. We sought to evaluate if Ki67 predicts progression of LGMCP after CRS/HIPEC. Methods A retrospective review of a prospectively maintained database was performed to identify patients treated with complete CRS/HIPEC for LGMCP from 2008-2019 with Ki67 assessed. Patient characteristics, histologic data, average and focally high (“hotspot”) Ki67 index, progression-free survival (PFS) and overall survival (OS) were analyzed. Ki-67 immunostain was performed on the histologic section with the highest cellularity and architectural complexity. Results Forty-four patients with LGMCP (55% male, median age 61) were identified. The median Ki67 score and hotspot Ki67 score was 15% (1-70) and 50% (1-90), respectively. On univariate analysis, average Ki67 and hotspot Ki67 were not predictive of PFS when analyzed as continuous normalized values (HR 1.0, p=0.79 and HR 1.1, p=0.38; respectively) or as categorical values when stratified by the median (HR 0.9, p=0.67 and HR 1.0, p=0.93). This remained true on multivariate analysis when stratified for peritoneal cancer index, CEA, and completeness of cytoreduction score for both normalized Ki67 and hotspot Ki67 (HR 0.9 [95% CI 0.8-1.3], p=0.94 and HR 1.04 [95% CI 0.8-1.3], p=0.73, respectively). Conclusion Ki67 failed to predict disease recurrence for patients with LGMCP in this cohort.