The Inheritance of Retinoblastoma and Its Relationship to Practical Eugenics*

In a brief review (5I), published several years ago, the author called attention to the fact that it was no longer possible to discuss the inheritance of predisposition to the development of neoplasms if all neoplasms were considered in one group. Satisfactory evidence was available even then that the significance of intrinsic factors, the part played by genes and by extrachromosomal factors, and the extent to which mendelian laws might be applied must be investigated separately for each kind of neoplasm. In respect to the etiology of some relatively common malignant neoplasms hereditary factors seemed to play but a minor part. Squamous cell carcinoma of the lip was an example of this group. At the other extreme were found neoplasms, both benign and malignant, in connection with which the hereditary pattern was obviously of considerable importance in etiology. For instance, this had long been known to be true of neurofibromas, particularly those of the type characterized clinically as "molluscum fibrosum." Similar evidence has continued to accumulate. Now that attention has been directed very largely toward extrinsic agents in the causation of neoplasms through progress in the investigation of chemical carcinogens and in the study of response of tissues to viruses, it appears to be timely to select a malignant neoplasm of known hereditary import for intensive study as to its familial behavior. This is done with no desire to detract from the importance of investigation of extrinsic agents, but rather to keep alive an appreciation of the significance of the intrinsic element in carcinogenesis. Retinoblastoma appears to be well suited to this purpose, since its multiple occurrence in families has led to numerous reports in medical literature which can be gathered for study. It presents