Familial Concordance of Thyroid and Other Head and Neck Tumors in an Irradiated Cohort: Analysis of Contributing Factors

Relatively little is known about variations in susceptibility to the effects of radiation in the general population. We have been studying 4296 individuals exposed as children to head and neck radiation. The present study was designed to evaluate the pattern of thyroid, parathyroid, salivary, and neural tumors in irradiated siblings for evidence of heritable susceptibility factors. We also wanted to determine whether the characteristics of thyroid cancers were influenced by familial factors. The following criteria were met by 251 sibling pairs: both irradiated, both with follow-up (average, 44.3 ± 9.4 yr; range, 9.4–59.5 yr), and both with organ-dose estimates. For each sibling pair we derived a quantitative score, taking into account the length of follow-up and known risk factors, for their concordance and used the sum of these scores to characterize the population. Whether we used thyroid cancer or all thyroid nodules as an end point, the degree of concordance did not exceed what could be explained by the length of follow-up and known risk factors. For thyroid cancer, neither the presenting characteristics nor their rates of recurrence were influenced by their concordance status. In summary, we were unable to identify familial factors that modify the strong effects of radiation exposure. There is no reason to alter the evaluation or treatment of thyroid cancer in an irradiated patient based on whether another member of the family has radiation-related tumors.