Retinoblastoma Occurring in One of a Pair of Identical Twins

The recorded incidence of retinoblastoma among twins is exceptionally low, and many of the reports are incomplete. The mean frequency of twinning in United States is 1 in 86 births, with one-fourth to one-third being reported as monozygous. One would expect a higher incidence of retinoblastoma occurring among twins, and in particular identical twins, than the literature reveals. Four pairs of monozygosity and probably four others, in which each of the twins developed retinoblastoma are recorded.1,2 In one of the pairs of monozygosity quoted by François, namely that of Duncan and Maynard, there is no evidence to show that the twins were definitely monozygotic.3 Walker *4 has reported the only occurrence of retinoblastoma in one of a pair of identical twins. Six cases of dizygotic twins are recorded, and in only one pair both twins were affected.2Table 1 summarizes the recorded cases of twinning and retinoblastoma