Clinical significance of Bacteroides fragilis as a potential prognostic factor in colorectal cancer

Bacteroides fragilis is considered to act in an anti-inflammatory manner on the intestinal tract. On the contrary, enterotoxigenic B. fragilis (ETBF), a subtype of B. fragilis, produces an enterotoxin (BFT; B. fragilis toxin), leading to asymptomatic chronic infections and colonic tumor formation. However, the impact of B. fragilis and ETBF on the clinical outcome of colorectal cancer (CRC) remains unclear. We aim to assess whether their presence affects the outcome in patients with CRC after curative resection. We obtained 197 pairs of matched formalin-fixed paraffin-embedded samples from cancerous and adjacent non-cancerous tissues of patients with pathological stage (pstage) II and III CRC after curative resection. The presence ofB. fragilisand ETBF were estimated using real-time polymerase chain reaction, and recurrence-free survival (RFS) and overall survival (OS) of the patients were analyzed. 16S rRNA for B. fragilis and bft DNA were detected in 120 (60.9%) and 12 (6.1%) of the 197 patients, respectively. B. fragilis-positive patients had better RFS than B. fragilis-negative patients, although that was not statistically significant. In subgroup analysis, better outcomes on RFS were observed in the presence of B. fragilis in pstage II and left-sided CRC. The association of B. fragilis positivity on OS was accentuated in the depth of the T4 subgroup. No significant differences were observed in RFS and OS between ETBF and non-toxigenic B. fragilis. Our findings suggest that the presence of B. fragilis is associated with better outcomes in patients with pstage II and III CRC after curative resection. •Bacteroides fragilisis generally indicated anti-inflammatory in the intestinal tract.•EnterotoxigenicB. fragilishas been reported to cause chronic colitis and tumours.•B. fragilis-positive patients had better relapse-free survival than those without it.•B. fragilis may predict better outcomes after curative resection.