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Pantomography of the mandible was performed in 98 patients with sporadic colorectal adenocarcinoma. Twenty-eight patients (29%) had osteomas versus 5% in a control group (P < 0.001). Mandibular osteomas are found in most patients with the premalignant dominant syndrome familial adenomatous polyposis. Sporadic colorectal cancer examinations of married couples have shown that diet has only a moderate influence on the development of colorectal cancer, whereas pedigree studies indicate a genetic component. On this basis we conclude that mandibular osteomas are probably genetic markers of the development of sporadic colorectal carcinoma.

One hundred and seventy-six individuals with various colorectal diseases were investigated simultaneously for increased in vitro tetraploidy in dermal fibroblast cultures and for occult mandibular osteomas. In only 10 of the 176 persons were both presumed markers of colorectal genetic predisposition present in the same individual. No evidence was found that these traits are causally associated. A combination of the two presumed markers showed a tendency towards occurrence in individuals with a positive family history of colorectal cancer among first-degree relatives.

Orthopantomography of the mandible was carried out on 50 patients with colorectal cancer without known familial disposition. Twelve patients (24%) had osteomas, as against 5% in the control group (P less than 0.001). Since an increased occurrence of mandibular osteomas has earlier been demonstrated in cases of familial polyposis coli and the family cancer syndrome, we must conclude that genetic factors are presumably of more importance in the development of colorectal cancer than previously assumed.

Orthopantomography of the mandible (OTM) showed osteomas in 3 of 34 non-affected sibs and children of the probands in 14 families with polyposis coli. The observed to expected ratio with osteomas was 0.35, which is not significantly lower than 1.0 and in accordance with the frequency in the normal population. Although the result does not enable a definite evaluation of the diagnostic value of OTM, the finding suggests that this method may be used as a supplement to regular proctosigmoidoscopic screening of first-degree relatives of polyposis patients.

One hundred and seven patients (57 patients with ulcerative colitis and 50 controls) were investigated for in vitro tetraploidy (IVT) in dermal fibroblast monolayer cultures. There was no difference in incidence of IVT between patients with ulcerative colitis and controls. We advance the hypothesis that the genetic background of the colorectal cancer type found in ulcerative colitis differs from that found in the colon cancer syndromes and in non-hereditary colorectal cancers. Colorectal cancer in ulcerative colitis is probably only dependent on the degree of inflammatory lesions of the colonic mucosa.