A rare case of subungual fibro-osseous pseudotumor of the digits in a 59 year old woman is reported. A painful polypoid mass with ulcerative changes was noted in the subungual portion of the right first toe. Macroscopically, the tumor arose chiefly in the subcutaneous region and was unrelated to the underlying bone tissue. Histologically, the lesion contained fibroblast-like tumor cells producing an extensive osteoid substance in a granulation-like background. Although it was necessary to distinguish the lesion from extraskeletal osteosarcoma, the tumor cells lacked prominent atypical features. It is considered that pathologists and clinicians should add fibro-osseous pseudotumor of the digits to the differential diagnosis of subungual tumor.

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True pulmonary carcinosarcoma (squamous cell carcinoma and chondrosarcoma) originating in the right lower lobe in a 62‐year‐old Japanese male is reported. The tumor, measuring 5.5×3.5×3.5 cm, was markedly necrotic and its apex protruded into the bronchial lumen. Light microscopy showed that the tumor was composed of squamous cell carcinoma with sarcomatous spindle or polygonal cell proliferation and true chondrosarcoma. Immunohisto‐chemically, the cytoplasm of numerous cells of the squamous cell carcinoma component was stained with anti‐cytokeratin (PKK 1) and the cytoplasmic membrane with anti‐epithelial membrane antigen (EMA). Although sarcomatous regions were stained with anti vimentin (vimentin) and no tumor cells were reactive for EMA, a few tumor cells were positive for PKK 1. The cytoplasm of numerous chondrosarcoma cells was positively stained for vimentin and S‐100 protein. Based on these findings, we concluded that the present tumor was a true carcinosarcoma composed of squamous cell carcinoma with sarcomatous regions and true chondrosarcoma Acta Pathol Jpn 42: 751–754, 1992.

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