Clinico-genetical analysis of colonic cancer. I. Occurrence, frequency in families and segregation analysis

The data on clinico-genealogic studies of colon cancer are presented. 694 families were examined with 432 probands having rectal and 262 colonic carcinoma among them. Clear family accumulation of colon cancer (2.4 +/- 0.35%) as well as other malignant tumors (6.8 +/- 0.6%) (p less than 0.01) was shown among the relatives of the first degree of relation. The values of segregation rates obtained for clinical forms of colon cancer were lower than theoretically expected for simple monogenic types of inheritance. The analysis of incomplete penetration of genotypes showed that, though formally the inheritance of colon cancer and its clinico-anatomical forms may be described by quasi-dominant types of inheritance, the penetration values are very low: from 4.3 to 13.3% for homozygotes and from 2.1 to 6.6% for heterozygotes. It shows that the supposition about the monogenic types of the colon cancer inheritance is doubtful and suggests that the colon cancer is to be regarded on the basis of the multifactorial model.