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The retinoblastoma protein (pRB), p16, and cyclin D1 are major components of the RB pathway, which controls the G1 checkpoint of the cell cycle. Proper regulation of this pathway is crucial for normal cell proliferation. Abnormal forms of these proteins have been found in various types of malignant tumours. In the present report, immunohistochemical techniques were applied to study the expression of pRB, p16, and cyclin D1 in 161 samples of primary small cell lung cancer (SCLC) and 20 samples of non‐small cell lung cancer (NSCLC). While pRB and cyclin D1 staining was negative in 161 specimens of SCLC, expression of p16 was observed in 153 samples. In contrast to SCLC, 16 out of 20 NSCLC cases exhibited pRB expression and 15 showed cyclin D1 expression, but only very weak p16 staining was found in five samples. These observations could provide additional criteria for the distinction between SCLC and NSCLC. Furthermore, these findings, based on primary tissues, implicate different mechanisms in the tumourigenesis of SCLC and NSCLC. Copyright © 1999 John Wiley & Sons, Ltd.

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Two cases of osteoclast-type giant cell tumour of the pancreas (OGTP) are presented and compared with similar tumours of other locations and pancreatic carcinomas. One of the tumours was analyzed by immunohistochemical methods. The mononuclear stromal cells and osteoclast-like giant cells, which characterize this very rare neoplasm, reacted with an antibody against vimentin, but were not decorated by antibodies against lysozyme, alpha-1-ACHT, alpha-1-AT. Pleomorphic mononuclear cells in osteoid additionally contained osteonectin and could thus be identified as osteoblasts. Only the tumour glands stained positively with panepithelial keratin antibodies and antibodies against the keratin polypeptides 7, 18, 19. These results demonstrate for the first time the mesenchymal differentiation of the OGTP, which in some cases is also able to form epithelial structures. The immunohistochemical reactions and the characteristic morphology of the tumour show the OGTP to be an entity which must be differentiated from pancreatic carcinoma, especially from its giant cellular subtype.