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The cellular and biochemical mechanisms that direct destruction of bone at the site of tumor osteolysis are unknown. In order to understand this process better, a murine model designed for the study of tumor osteolysis was developed and the influence of osteolytic and nonosteolytic tumors on bone was investigated. Tumors developed following femoral intramedullary injection of sarcoma (2472) and melanoma (G3.26) cell lines; however, only tumors from the 2472 cell line caused osteolysis. It was determined that 2472 tumor-induced osteolysis commenced 6 days after the femora had been inoculated with 2472 cells. There were more osteoclasts per millimeter of bone surface in 2472 tumor-bearing limbs (16.7 +/- 5.0) than in sham-injected limbs (3.8 +/- 0.9) (p < 0.015). In addition, an increase in the osteoclast size (area) was detected in 2472 tumor-bearing limbs: 412 +/- 65 micron2 compared with 187 +/- 17 micron2 (p < 0.01). In vitro bone resorption experiments indicated that 2472 tumor cells had a limited ability to destroy bone in comparison with macrophages and osteoclasts. Taken in total, these findings define a model that is useful for the study of tumor osteolysis, and the data from analyses of the model demonstrate that the cellular mechanisms responsible for 2472 tumor-induced osteolysis include both an increase in the number of osteoclasts and activation of mature osteoclasts.

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Histologic sections of seven sequamous cell carcinomas (SCC), 13 basal cell carcinomas (BCC), and a bowenoid actinic keratoses were examined for expression of HLA class 1 antigens (HLA‐ABC) using a monoclonal antibody and an immunoperoxidase technique. Expression of β2‐microglobulin was examined with a polyclonal antibody method. Neither cell marker was detected within the Bowwenoid actinic keratoses. Squamous cell carcinomas and basla cell carcinomas exhibited decreased expression of both HLA‐ABC and β2‐microglobulin and often did not express these antigens at all. HLA‐ABC was present in only two of 13 basal cell carcinomas and four of seven sequamous cell carcinomas. β2‐microglobulin was present in one of 13 basal cell carcinomas and two of seven squamous cell carcinomas. When present, these antigens other. In both SCC and BCC, both antigens were usually lost simultaneously. In all tumors with β2‐microglobulin, HLA‐ABC and β2‐microglobulin on their surfaces, the absence of these antigens is not an absolute marker for malignanancy.