What is the relationship between Streptococcus (Strep) bovis bacteremia and colon malignancy?

Relationship Between Streptococcus bovis Bacteremia and Colon Malignancy

Streptococcus bovis bacteremia, particularly the S. gallolyticus subspecies, has a strong and well-documented association with colonic neoplasia, most commonly adenomas and carcinomas, requiring colonoscopy for all patients with S. bovis/S. gallolyticus bacteremia to rule out occult colon cancer. 1

Epidemiology and Clinical Significance

• S. bovis bacteremia is strongly associated with colonic neoplasia, with studies showing 25-80% of patients with S. bovis/S. gallolyticus bacteremia having concomitant colorectal tumors 2
• The strongest relationship is with the S. gallolyticus subspecies (formerly known as S. bovis biotype I), which has been specifically linked to gastrointestinal neoplasia 1
• In patients with S. bovis bacteremia who undergo colonoscopy, approximately 30-40% are found to have colorectal adenocarcinoma 2, 3
• Female patients and those with a history of non-colorectal malignancy may have higher rates of colorectal adenocarcinoma when S. bovis bacteremia is detected 2

Pathophysiology

• The exact mechanism of this relationship remains debated - it's unclear whether S. bovis/S. gallolyticus infection is merely a consequence of the gastrointestinal lesion or if it could potentially trigger or promote colorectal cancer 1
• S. bovis is considered part of the normal intestinal flora, but its presence in the bloodstream may indicate disruption of the intestinal barrier, potentially due to neoplastic lesions 3
• Studies have demonstrated a clear relationship between positivity for S. bovis in colonic fluid and findings of malignant tumors and large polyps in the colon 3

Clinical Recommendations

• All patients with S. bovis/S. gallolyticus bacteremia should undergo colonoscopy to rule out occult colon cancer during hospitalization 1
• In the absence of any tumor found during initial evaluation, annual colonoscopy is highly suggested for continued surveillance 1
• This recommendation applies to all subspecies of S. gallolyticus (including S. gallolyticus subsp. pasteurianus, formerly bovis biotype II), as emerging evidence suggests similar associations with colonic neoplasia 4
• Proper microbiological classification of S. bovis isolates is essential, as different subspecies may have varying strengths of association with colorectal malignancy 1

Beyond Colorectal Cancer

• S. bovis bacteremia has also been associated with extracolonic malignancies, with approximately 32% of adult patients having invasive cancer of any type 5
• Infective endocarditis is a common presentation of S. bovis bacteremia and may be the initial manifestation that leads to the discovery of an underlying malignancy 1
• Other species of Streptococcus viridans, beyond S. bovis, may also be associated with colonic malignancies, though this relationship is less well established 6

Pitfalls and Caveats

• Failure to recognize the association between S. bovis bacteremia and colonic neoplasia may result in missed opportunities for early cancer detection 4
• The reclassification of S. bovis into multiple subspecies (particularly S. gallolyticus) in 2003 may cause confusion among clinicians who are familiar with the older nomenclature 4
• Serology-based detection of colorectal cancer using serum IgG concentrations against S. bovis antigens lacks sensitivity and specificity and is not recommended as a screening tool 1
• FDG PET/CT, while increasingly used in the diagnostic workup of infective endocarditis, has not been specifically studied for detection of occult colorectal cancer in patients with S. bovis/S. gallolyticus bacteremia 1