Rhabdoid tumour of the lung is a dedifferentiated phenotype of pulmonary adenocarcinoma

Aims: Primary rhabdoid tumour of the lung is rare, and histological and bio logical characteristics have not been fully documented. We describe three c ases of primary lung rhabdoid tumour, all associated with adenocarcinoma, a nd investigate the histological features and biological characteristics. Methods and results: Three cases were obtained from a total 902 cases of su rgically removed primary lung tumours between 1986 and 1998. The rhabdoid c ells were found to occupy about 50-90% of each tumour. All of the tumours h ad nonrhabdoid adenocarcinoma foci in the centre of the tumours. Transition between the adenocarcinomatous and rhabdoid components was demonstrated. D etailed immunohistochemical studies were carried out. The epithelial marker s, cytokeratins and epithelial membrane antigen (EMA), were strongly expres sed in rhabdoid and adenocarcinomatous components. Furthermore, surfactant apoprotein A was positive in both components in one case, but myoglobin, My oD and HHF35 were not expressed. Vimentin was strongly and diffusely staine d in all cases. The neuroendocrine markers, chromogranin A (all cases), neu ron-specific antigen (NSE) (two cases) and CD56 (one case) were occasionall y positive in only a small number of the rhabdoid tumour cells. GM-CSF was positively stained in one case, and the dedifferentiated characteristics of the rhabdoid cells was suggested. Proliferative cell nuclear antigen (PCNA ) was strongly demonstrated in the rhabdoid tumour cells (all cases). To ga in better understanding the highly proliferative characteristics of the tum ours, p53 gene (exons 5-8) mutation was examined by DNA sequencing analysis ; mutation of the p53 DNA was not detected. Overexpression of p53 protein w as also not demonstrated in all cases. HPV6 was demonstrated in one case by PCR method and also non-isotopic in-situ hybridization (NISH). Two cases d ied in a short period of time (3 years and 4 months, respectively). Conclusion: The rhabdoid cells in these three cases were considered to repr esent the dedifferentiated components of the accompanying adenocarcinoma. D edifferentiated characteristics (neuroendocrine markers, GM-CSF vimentin, a nd the aggressive behaviour) were evident.