Loss of heterozygosity on chromosome 13 and its association with delayed growth of retinoblastoma

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Abstract
Loss of heterozygosity (LOH) on chromosome 13 and the age of patients at operation were studied in 46 cases of retinoblas-toma (RB) tumors, of which 25 were hereditary and 21 were non-hereditary. The frequency of LOH was 70% for all informative tumors, but significantly higher in non-hereditary tumors (90%) than in hereditary ones (52%). Our results suggest that LOH might be involved in the initial somatic events in non-hereditary tumors. Age at operation of patients with hereditary tumors was significantly lower than that of patients with non-hereditary tumors. Even when tumors associated with a family history were omitted from among the hereditary cases, the difference was still significant. In the case of hereditary tumors, age at operation of LOH-negative patients was significantly lower than that of LOH-positive patients. When tumors associated with a family history were omitted, the difference was still significant. The delay in development of LOH-positive tumors suggests that LOH for one chromosome 13 may be disadvantageous with respect to growth of RB tumors.