The prognostic relevance of histologic subtype in appendiceal adenocarcinoma

Background: The aim of this population-based study was to determine the prognostic value of the histologic subtypes mucinous (MAC), non-mucinous (AC) and signet ring cell (SRCC) adenocarcinoma among patients with appendiceal cancer.

Methods and materials: Data from the Netherlands Cancer Registry (NCR) of patients with primary appendiceal adenocarcinomas with MAC, AC and SRCC histologic subtype, diagnosed between 2001 and 2015 were used (n = 675). To categorize patients according to the recent histopathological classification, the NCR was linked with the Dutch Pathology Registry (PALGA). Log-rank tests and Kaplan-Meier analyses were performed to estimate overall survival (OS), and the cox proportional hazards model was run to identify prognostic factors.

Results: AC was the most frequently encountered histologic subtype (50.9%), followed by MAC (35.8%) and SRCC (13.3%). In locoregional disease, histologic subtype was not a prognostic factor for OS with 5-year survival rates for patients with AC, MAC and SRCC of 60.0%, 60.5% and 69.6% respectively (p = 0.68). Metastatic disease was more common in SRCC (53.8%) than in MAC (38.8%) and AC (23.4%) (p < 0.0001). Median OS for patients with metastatic disease was 12.6, 27.7 and 18.2 months in AC, MAC and SRCC respectively (p < 0.005). MAC was associated with higher survival compared to AC (HR 0.48, 95%CI 0.34-0.69). In subanalyses, MAC was only a positive prognostic factor compared to AC in patients with peritoneal metastases (HR 0.42, 95%CI 0.28-0.62).

Conclusion: Histologic subtype had no prognostic relevance in locoregional or systemic metastatic disease in appendiceal adenocarcinoma. In peritoneal metastases, mucinous histologic subtype was a favorable prognostic factor, compared to non-mucinous and signet ring cell subtype.