In this issue, Tjalsma and colleagues from the University of Nijmegen Medical Center report on the detection of immune reactions against Streptococcus bovis antigens in sera of 11 out of 12 colon cancer patients and in 3 out of 4 patients with colon polyps. No positive reaction was observed in 8 control subjects. They used immunocapture tandem mass spectrometry to identify an immune reaction against bacterial antigens and found that one of the diagnostic antigens represents a surface-exposed heparin-binding protein that, according to their speculation, might be involved in the attachment of S. bovis to tumor cells. They claim that profiling of the humoral immune response against S. bovis infections may represent a promising diagnostic tool in early detection of human colon cancer. In spite of the still relatively low number of sera analyzed, these data are of substantial interest since they stress the possibility that this immune reaction may serve as a sensitive marker for early detection of colon neoplasias.
A large number of previous reports point to a close linkage between S. bovis infections and tumors of the human colon. Initially, a paper by McCoy and Mason appeared in 1951, suggesting a relationship between cancer of the colon and enterococcal endocarditis. 1 The coincidence of S. bovis septicemia and S. bovis endocarditis was noted in several subsequent publications, first reported in 1974 2,3 and confirmed shortly thereafter. 4-6 S. bovis endocarditis is considered to be a clinical indication for colonoscopy since the majority of these patients present with either colon carcinomas or colon polyps. [7][8][9][10] The same holds for bacteremias caused by S. bovis. [11][12][13][14][15][16] In the presence of a carcinoma of the colon, the relative risk for developing S. bovis-linked endocarditis is in the range of 3-6%. 17 Conversely, 65-70% of patients with S. bovis endocarditis simultaneously revealed not previously recognized malignant gastrointestinal tumors. 18,19 The high percentage of colon cancer found in patients with S. bovis endocarditis or septicemia has been explained by the fact that these bacteria can easily penetrate the blood stream in ulcerating carcinomas of the colon. This interpretation, however, finds little support by data demonstrating a high risk of S. bovis endocarditis and/or septicemic patients for nonulcerating adenomas. 6,13,[20][21][22][23] In addition, patients with a history of S. bovis endocarditis with no colonoscopic abnormalities at that time developed colon tumors 2-4 years later. 12,17,23 (This again does not seem to support such an interpretation.)
As shown by Tjalsma et al., 24 it is unlikely that the acquisition of serum antibodies to S. bovis antigens originates from antigen presentation due to bleeding from microlesions since antibody titers against lipopolysaccaride antigens of Gram-negative bacteria prevalent in the colon did not differ between colon cancer patients and controls, as also previously reported by Darjee and Gibb. 25