Fusobacterium nucleatum in appendiceal cancer: Prevalence and influence on the tumor immune microenvironment

Introduction

Fusobacterium nucleatum (Fn) has gained notoriety for its propensity toward mucosal invasion in acute appendicitis and its potential involvement in development or progression of colorectal cancer. We hypothesized that Fn may be linked to appendiceal cancer (AC). To explore the potential connection, we quantitatively examined the presence of Fn in appendiceal tissue across various histological diagnoses.

Methods

A total of 50 formalin-fixed paraffin-embedded tissues were obtained from archival appendectomy specimens. RNA-in situ hybridization (RNA-ISH) with an Fn-specific probe was performed, and immunohistochemical staining was performed on tumor-associated CD3 + and CD8 + lymphocytes. The digital images were analyzed using QuPath and Aperio ImageScope.

Results

RNA-ISH showed significantly higher Fn content in the appendiceal pathology with increased Fn levels in acute appendicitis, low-grade AC, and high-grade AC relative to the Fn level of a normal appendix. Also, Fn content was strongly associated with decreased CD8 + lymphocyte density within high-grade AC, but no significant association was found with CD3 + lymphocyte density and tumor grades.

Discussion

In this study, we confirmed previous reports of Fn levels within normal appendiceal tissue and acute appendicitis and extended this finding to a range of appendiceal neoplasms. The inverse relationship between Fn and CD8 + cell density within high-grade AC in our series also suggests a potential role for Fn in shaping the AC microenvironment toward an immune-suppressed or immune-excluded phenotype. Further study is planned to include larger case numbers with a wider variety of histological subtypes of AC and peritoneal metastatic lesions to enrich the understanding of the immunological and microbial microenvironment in AC for novel opportunities for targeted therapy.