Supernumerary ring chromosomes containing chromosome 17 sequences. A specific feature of dermatofibrosarcoma protuberans?

Mystery surrounds the mechanisms by which the uncommon cutaneous tumor dermatofibrosarcoma protuberans (DP) arises and progresses. A clue may be at hand in the form of extra abnormal chromosomes (one of three ring chromosomes per case with or without other chromosome abnormalities) seen in some 10 cases, including five cases in our experience. The specificity of the rings to DP would be enhanced if the rings were found to contain a contribution from a constant chromosome. We here report fluorescence in situ hybridization (FISH) results bearing on the chromosomal content of DP rings, together with clinical, pathologic, and cytogenetic documentation of our first two cases, which were briefly reported earlier, and three new DP cases. To dissect a translocation (in our 2nd case), we probed by FISH and discovered chromosome 17 sequences in the rings in all five DP cases. Nonfluorescent bands were seen on some rings painted with a whole chromosome 17 probe, indicating the presence in these rings of foreign chromosome sequences. The complexity of the rings was underscored by the detection in only one case of chromosome 17 centromeric sequences. The situation in DP seems to have parallels to that in well-differentiated liposarcoma, another tumor of intermediate malignancy with extra abnormal marker chromosome containing contributions from a constant chromosome and variable donors. In DP the supernumerary rings are clearly specific and significant.