“…The latter tumors are re garded as germinal mutations and hereditary, whereas this is assumed only in 10-15% of patients with unilateral affec tion [1,12]. At first glance Knudson's hypothesis of a two step mutation in pathogenesis of retinoblastoma could perhaps theoretical ly explain the similar histological features in the different neoplasms, if one could imagine that proliferation of germ cells is generally stimulated by an early mutation and the sec ond steps are delayed in different organic systems [13,14], This imagination would be supported by the clinical findings that the mean latent period to manifestation of second tu mors after cured retinoblastoma is 13 years and the highest incidence of germ cell malignancies of the ovary is noted in the second decade of life [8,15], But, in contradiction, germ cell malignancies in children previously treated for retino blastoma are a very rare event [1,7,8,16]. As a chromosomal deletion can be detected in about 10% in patients affected by retinoblastoma, we performed chromo somal analysis of blood lymphocytes with banding technique, which did not reveal any abnormal structure [17].…”