Supernumerary ring chromosomes and nuclear blebs in some low-grade malignant soft tissue tumours: atypical lipomatous tumours and dermatofibrosarcoma protuberans.

We investigated the diagnostic significance of supernumerary ring chromosomes in low-grade soft-tissue neoplasms. Chromosome slides were prepared from 123 samples of soft-tissue tumours using the standard trypsin-Giemsa banding technique. Supernumerary ring chromosomes were found in 6 cases of soft tissue tumours: 5 cases of atypical lipomatous tumour (ALT) and 1 case of dermatofibrosarcoma protuberans (DFSP). By chromosome painting with fluorescence in situ hybridization (FISH), the ring chromosome in 1 ALT was painted over its entire length with the chromosome 12 probe. Nuclear blebs and micronuclei, which were observed in each case of ALT, also contained chromosome 12 material; and these structures may represent a topological distribution of ring or giant marker chromosomes in the interphase nuclei. Our findings suggest that supernumerary ring chromosomes are characteristic of some low-grade soft tissue neoplasms including ALT and DFSP.