[Loss of heterozygosity in the progression of tumors]

Based on the two mutation hypothesis in the development of retinoblastoma, loss of heterozygosity (LOH) of specific chromosome has been implicated in the presence of tumor suppressor gene. Studies on the LOH in different types of tumors revealed that LOH of each chromosome might play a different role in the multistep process of carcinogenesis: LOH of some chromosomes may play an etiological role in the development of some tumors, while that of other chromosomes or the same chromosome in other tumors, may play a role in the progression of tumors. LOH of chromosome 13 is an example for the former cases, and the latter cases involve LOH of chromosome 17 in colorectal carcinoma and osteosarcoma, chromosome 10 in glioblastoma, chromosome 1 in neuroblastoma and malignant melanoma, and chromosome 11 in breast carcinoma. These studies indicates that the progressive or concerted LOH could be a measure of the highly malignant or metastatic potentiality. However, it should be borne in mind that, especially in polyploid tumors, LOH also occurs as a random event following the polyploidization-segregation process.