Homogeneously staining region in a retinoblastoma cell line: relevance to tumor initiation and progression

A human retinoblastoma cell line was found to contain a homogeneously staining region (HSR) on chromosome 1 (at 1p34). An HSR had previously been identified at the same site in a human neuroblastoma cell line. Of the original retinoblastoma line, a subpopulation was found which did not contain the 1pHSR but did contain a 3p+ chromosome in which the additional segment resembled a small HSR. The 3p+ was most likely the result of the translocation between the 1pHSR and the short arm of a chromosome 3. Preliminary results also indicate that the retinoblastoma cells with the 1pHSR produced tumors in athymic nu/nu mice in an average of 28 days, while identical numbers of the retinoblastoma cells with the 3p+ (probable HSR) produced tumors in an average of 75 days.