Bizarre parosteal osteochondromatous proliferation: a new cytogenetic subgroup characterized by inversion of chromosome 7.

Bizarre parosteal osteochondromatous proliferation (BPOP) is a rare, benign osteocartilaginous lesion characterized by a mixture of immature bone, bland spindle cells, and irregular, hypercellular cartilage undergoing calcification. A t(1;17)(q32;q21) has been reported as a unique recurring translocation identified in seven cases. Inversion of chromosome 7, inv(7)(q22q32), has also recently been described in one case of BPOP. We report an additional case of inv(7) in a BPOP occurring on the distal radius in a 36-year-old woman who presented with a slow-growing mass on the right wrist. Metaphase karyotype analysis of fresh tissue from tumor taken at resection revealed an inv(7)(q22q32). A review of the literature identified two additional cases of inv(7) (q21.1q31.3 and q22.1q31.3), both paired with inv(6)(p25q15), bringing the total number of cases of inv(7) in BPOP to four. These data suggest inv(7) may be another characteristic cytogenetic abnormality associated with and possibly contributing to the development of BPOP.