Borderline chondrosarcoma of long and flat bones.

We reviewed histological and clinical findings of six cases of borderline chondrosarcoma and examined the expression of collagen types I, II, III, V, and VI by immunohistochemical analysis of these tumors. Borderline chondrosarcoma is defined as a cartilaginous tumor of bone resembling enchondroma on the basis of histomorphology. Clinically the tumor causes intermittent vague pain unrelated to physical activities. On radiographs borderline chondrosarcoma is characterized by evidence of endosteal erosion. We observed local recurrences in two cases treated by intralesional excision and marginal excision, and one of those cases died of inoperable local tumor recurrence. In our histological analysis based on tissue patterns, there were enchondromatous patterns in five cases, and chondrosarcomatous patterns in four cases. In the second recurrent tumor in one case, a chondrosarcomatous pattern was newly observed, and the recurrent tumor was found to be a low-grade chondrosarcoma cytologically in the other case. In the tumor matrix immunoreactivity for collagen types II and VI was predominant, with collagen types I, III, and V showing heterogeneous expression in some cases. In all cases rimming of tumor lobules with collagen types I and V was absent. Immunoreactivity for collagen type II in the cytoplasm of tumor cells was found in four cases and all three recurrent tumors. Borderline chondrosarcoma, as defined by histology, clinical symptoms and radiological appearance, shows a collagen distribution pattern similar to that of low-grade chondrosarcoma. These findings are in accordance with the clinical outcome of borderline chondrosarcoma which parallels that of low-grade chondrosarcoma. Thus borderline chondrosarcoma may be best treated by wide en-bloc excision rather than curettage.