Secondary osteosarcoma: is there a predilection for the chondroblastic subtype?

Osteosarcoma is the most common form of primary bone cancer in the adolescent and young adult patient population. Outcomes in patients with secondary osteosarcoma are inferior compared with outcomes in patients with primary osteosarcoma. The goal of this study was to investigate whether there is a predilection for the chondroblastic histologic subtype in secondary osteosarcoma. A retrospective chart review was performed to identify cases of secondary osteosarcoma treated at 1 institution from 1991 to 2012. Histologic subtypes were evaluated by a pathologist, and a review of the literature was also performed to identify the histologic subclassification of additional series of secondary osteosarcomas. Of a total of 131 cases of osteosarcoma, 9 (6.9%) were identified as a secondary malignancy. Only 2 cases (22%) were identified as chondroblastic variants, although 6 (67%) showed some degree of chondroid differentiation. Of the 3 cases meeting the criteria for postradiation osteosarcoma, 2 (67%) were identified as chondroblastic variants and all 3 showed some degree of chondroid differentiation. Five other studies evaluating histologic subtypes in postradiation osteosarcoma showed a cumulative frequency of 20% for the chondroblastic variant. Although the study results did not support the hypothesis of an association between secondary osteosarcoma and the chondroblastic subtype, the high proportion of cases of postradiation osteosarcoma with the chondroblastic subtype and the even higher proportion showing some degree of chondroid differentiation are noteworthy features of this disease.