Malignant Tumors among Twins: A Study of Divergent Views

Summary Agreement prevails that MZ twins have higher concordance rates for cancer than do DZ twins. The exact genetic influence on concordance remains doubtful. Neither the patient groups nor the means by which data are analyzed are comparable. The naturally higher perinatal mortality rate among twins affects statistical analysis of diseases among surviving cotwins. Classification of zygosity among all studies of twins is not entirely reliable. A review of published reports of cancer among twins notes concordance in a variety of tumors. Genetic factors appear to operate either in the concordance of the cancer or in the site of the specific tumors. A genetic origin of tumors in MZ twins is possible. Tumors, including type, site, and age of onset, affect MZ twins more than both members of a DZ pair. Computerized permanent twin registers should be established for study of prospective follow-up of large twin populations. Suggestions are made for implementation.