Chromosomal microarray analysis of benign mesenchymal tumors with RB1 deletion

Spindle cell lipomas/pleomorphic lipomas, mammary-type myofibroblastomas, and cellular angiofibromas are benign mesenchymal tumors that demonstrate histologically overlapping features but with varying anatomic locations and an uncertain etiologic relationship. These tumors have also been found to have an overlapping molecular profile with shared 13q14 deletions, which is the location of the tumor suppressor gene RB1 that encodes the retinoblastoma protein. Molecular studies thus far have largely focused on the RB1 locus, using primarily immunohistochemistry and fluorescence in situ hybridization to characterize RB1 status. However, further characterization of the molecular profile of these lesions, including genome-wide copy number variation, remains to be well defined. The goal of this study is to further characterize the specific RB1 deletions seen in spindle cell lipomas/pleomorphic lipomas, cellular angiofibromas, and mammary-type myofibroblastomas as well as to evaluate these neoplasms for additional molecular abnormalities using the OncoScan™ CNV Plus Assay, which is used for clinical use as a whole-genome copy number microarray-based assay. Ten of eleven cases demonstrated deletion of the RB1 gene with varying deletion size and breakpoints. The majority of additional genetic alterations were chromosomal losses and loss of heterozygosity with rare chromosomal gains. Although only a small subset of mesenchymal neoplasms was evaluated, the principle of creating a novel pairing of the molecular method with the tumor type represents a promising avenue for further study in a variety of tumors.