BACKGROUND:The World Health Organization's histologic classification of bone tumors was revised in 1993.METHODS:The first edition was reviewed by an international panel of pathologists from nine countries and modified to incorporate advances made in the twenty years since it appeared.RESULTS:The framework and concept of the classification remain the same (i.e., based on histologic criteria in terms of differentiation shown by the tumor cells via conventional light microscopy supplemented by immunohistochemistry). New entities not described in the first edition include, for example, benign and malignant fibrous histiocytomas, well differentiated osteosarcoma, round-cell osteosarcoma, clear cell chondrosarcoma, primitive neuroectodermal tumor of bone, osteofibrous dysplasia, and giant cell reparative granuloma.CONCLUSION:The revised and expanded classification reflects advances in our knowledge, but is similar in concept and framework to the original version to allow comparisons between data collected in the past and future.

Quantification of argyrophilic nucleolar organizer regions has been proposed as a technique that may aid in diagnosing and predicting the biologic behavior of a variety of neoplasms. A 1-step silver staining technique was used to identify and quantify argyrophilic nuclear organizer regions in a series of 96 bone tumor specimens. Malignant bone tumors had a higher mean argyrophilic nuclear organizer region count (3.05 +/- 0.82) than giant cell tumors (1.39 +/- 0.14, p < 0.001) and benign bone tumors (1.51 +/- 0.42, p < 0.001). Despite these differences in mean counts, an overlap of argyrophilic nuclear organizer region scores was observed in some benign and malignant cases. The argyrophilic nuclear organizer region counts of the osteosarcomas were analyzed to determine whether they correlated with tumor behavior. The mean argyrophilic nuclear organizer region count of specimens from patients in whom metastatic disease developed was not significantly different than that of patients who remained disease free.

Giant cell tumors in the small bones of the hand are unusual, particularly in the carpus. A 28-yearold woman developed a giant cell tumor in the capitate. After biopsy, she was treated with complete excision of the capitate with no reconstruction. Five years later she had excellent hand function and no tumor recurrence. A careful roentgenographic and pathologic examination will distinguish between aneurysmal bone cysts and giant cell reparative granulomas. Complete excision of the involved bone is recommended.

Giant cell tumour (GCT) of bone is an uncommon neoplasm, representing approximately 5% of all bone neoplasms and approximately 21% of benign bone tumours (Dahlin & Unni, 1986). The vast majority of GCTs arise after closure of the growth plate and occur at the end of long bones. GCTs are frequently diagnosed by radiologists because of their preferred location (80% in long bones of the extremities), age distribution (peak incidence in the third decade) and morphologic appearance. Typically, they are expanding radiolucent lesions eccentrically located, most commonly at the articular surface of a long bone. Pathologic and histologic findings are characteristic, although these tumours need to be differentiated from other lesions containing giant cells, such as non-ossifying fibroma, aneurysmal bone cyst, osteoblastoma, chondroblastoma, giant cell reparative granuloma, benign fibrous histiocytoma and brown tumours. The biologic behaviour of GCT frequently is not predictable. In our experience, shared by most authors, histologic grading as a guide to prognosis is of no practical value (Schajowicz, 1981). On the contrary, radiologic features (“quiescent”, “active”, “aggressive”) are a more reliable indication of local clinical behaviour (Campanacci et al, 1987). GCTs are often aggressive in behaviour with a distinct tendency toward local recurrence, most often within the first post-operative years (McDonald et al, 1986). We present a collection of unusual GCTs (excluding those of the facial bones) from 465 histologically proven cases from the Latin American Tumor Registry and St Louis University.

In conclusion, while similar histologically, osteoid osteoma and osteoblastoma have the potential of being significantly different clinically. Osteoid osteoma tends to be a problem of pain and not of great oncologic significance. Osteoblastoma, on the other hand, has the potential for local bone destruction and aggressiveness as well as the rare occurrence of metastases. For this reason, the latter tumor needs to be respected from an oncologic standpoint and appropriate surgical excision performed.

Three cases of adamantinoma of the tibia associated with and mimicking fibrous dysplasia or osteofibrous dysplasia are reported in children aged three, nine, and 16 years. The roentgenographic features were typical of intracortical fibrous dysplasia (osteofibrous dysplasia). These entities are not two distinct diseases, but rather are different histologic expressions of essentially the same process, which varies depending on location (predominantly intracortical or medullary) and age. Adamantinoma in children under ten years of age is not as rare as reported in the literature and was found in two of 14 cases in our files (14.3%). In some cases the fibrous dysplasialike component predominates over the scarce epithelioid islands of tumor cells and consequently is not recognized as adamantinoma. That may explain the frequent recurrences after incomplete excisions of supposed intracortical fibrous dysplasia lesions in young children. An extensive histopathologic study of the biopsy and/or surgical specimen by a specialized pathologist is therefore advisable.

In this review are discussed a small group of bone tumors that present the greatest and sometimes unresolved problems in diagnosis, not only for the clinician but also for the pathologist, even with full knowledge of the clinical and roentgenologic presentation. The following neoplastic lesions are described in detail: cartilage-forming tumors, bone-forming tumors (with special emphasis on aggressive or malignant osteoblastoma), and round-cell tumors of bone. This last group presents a special challenge to the pathologist even after histopathologic examination. Some newer, more sophisticated methods are discussed, especially those applied in the differential diagnosis of Ewing's sarcoma and tumors of neuroectodermal origin.

The effect of preoperative radiation therapy on the pseudocapsule of experimental rat soft-tissue sarcomas has not been histologically evaluated in a controlled study. The irradiated animal showed marked thickening of the capsular structure surrounding the sarcoma. Everywhere morphologically distinct from the tumor, there was no evidence of tumor invasion into or through this capsular structure. The membrane was consistently thicker and more hyalinized than in the control animals. The nonirradiated animals showed a minimal pseudocapsular structure with a characteristic tumor penetration. Irradiation produced distinct histologic changes in the pseudocapsule. Although assumed on the basis of clinical observations alone, irradiation-induced pseudocapsule has not previously been demonstrated in an experimental model of soft-tissue sarcoma.

Two men, aged 68 and 77 years, had metastases of carcinoma in pagetic bones. These cases were initially diagnosed clinically as Paget's sarcoma. Roentgenograms, scintigrams, and bone puncture biopsy specimens (BPBs) of the right scapula and the sacrum, respectively, showed only Paget's disease. However, an additional BPB obtained with the aid of computed axial tomography (CAT) revealed the presence of metastases of lung carcinoma in the right scapula and of a carcinoma of probable prostatic origin in the pagetic sacrum in the other. The observations testify to the usefulness of CAT-directed BPB when Paget's sarcoma is suspected, especially in cases located in the scapula, pelvis, or spine.

Malignant bone-forming tumors that arise from the surfaces of long bones are far less common than those that arise from within bone. These surface osteosarcomas are clinically and radiographically similar, yet histologically they are quite distinct. In reviewing the literature, we classified the tumors according to three subgroups: parosteal (juxtacortical) osteosarcoma, periosteal osteosarcoma, and high-grade surface osteosarcoma. We also studied the clinical, radiographic, and histological findings in eighty patients who had been treated for an osteosarcoma over a forty-four-year period. Adequate follow-up data existed for forty-eight of the eighty patients. The duration of follow-up ranged from two to fifteen years after the initial operation (amputation or resection). Patients who had a parosteal osteosarcoma had the best prognosis; those who had a periosteal osteosarcoma, the next best; and those who had a high-grade surface osteosarcoma, the poorest. Because of these widely varying prognoses, the lesions require different treatment.

The cases of twenty-six patients who received a massive allotransplant of frozen bone, with a known degree of histocompatibility between the donor and the recipient, were studied. Twenty-two patients were followed for more than two years (range, twenty-four to ninety-two months). Twenty-three biopsies were performed in sixteen patients from nine to seventy-eight months after transplantation. No clear relationship could be established between the degree of histocompatibility of the donor and the recipient and the incorporation of the graft, probably in part due to the number of variables involved and the polymorphism of the HLA system. However, no early massive resorption of the transplant was seen in this series, in which, by the design of the protocol, no recipients had pre-existing circulating antibodies to the antigens of the donor. Two allografts showed infiltration by round cells and vascular lesions in the absence of infection, which is suggestive of an immune response against antigens from the donor. Both matched poorly with the donor for HLA antigens. The individual who had the strongest reaction was the only recipient in the series who had a massive failure of the transplant.