Coexistence of neocentromeric marker 3q and trisomy 3 in two different tissues in a 3-year-old boy with peripheral T-cell lymphoma: support for a gene dosage effect hypothesis.

A very small supernumerary de novo marker chromosome was ascertained during cytogenetic diagnosis of a 3 1/2-year-old boy with peripheral T-cell lymphoma, unspecified. The marker, which was C-band and alpha-satellite DNA negative, was identified in the pleural effusion and involved cervical lymph node whereas the involved bone marrow cells had trisomy 3 as a clone. The neocentromere marker was characterized by multiple probes demonstrating an inversion duplication of the distal portion of chromosome 3q involving the BCL6 gene. Whole or partial trisomy 3q represents one of the most recurrent chromosomal abnormalities occurring in T-cell lymphomas, suggesting that the 3q contains a critical region for the pathogenesis of T-cell lymphoma. Our present case showed that the critical region may reside within the neocentromere marker 3q27~q29 in this case in particular and revealed a different mechanism in increasing gene dosage rather than gene disruption. In addition, this type of neocentromere is one most often reported in constitutional cases. Here, we report its presence in cancer for the first time.