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

Primary rhabdoid tumour of the lung is rare, and histological and biological characteristics have not been fully documented. We describe three cases of primary lung rhabdoid tumour, all associated with adenocarcinoma, and investigate the histological features and biological characteristics.

Three cases were obtained from a total 902 cases of surgically removed primary lung tumours between 1986 and 1998. The rhabdoid cells were found to occupy about 50-90% of each tumour. All of the tumours had nonrhabdoid adenocarcinoma foci in the centre of the tumours. Transition between the adenocarcinomatous and rhabdoid components was demonstrated. Detailed immunohistochemical studies were carried out. The epithelial markers, cytokeratins and epithelial membrane antigen (EMA), were strongly expressed in rhabdoid and adenocarcinomatous components. Furthermore, surfactant apoprotein A was positive in both components in one case, but myoglobin, MyoD and HHF35 were not expressed. Vimentin was strongly and diffusely stained in all cases. The neuroendocrine markers, chromogranin A (all cases), neuron-specific antigen (NSE) (two cases) and CD56 (one case) were occasionally 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 gain better understanding the highly proliferative characteristics of the tumours, p53 gene (exons 5-8) mutation was examined by DNA sequencing analysis; mutation of the p53 DNA was not detected. Overexpression of p53 protein was 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 died in a short period of time (3 years and 4 months, respectively).

The rhabdoid cells in these three cases were considered to represent the dedifferentiated components of the accompanying adenocarcinoma. Dedifferentiated characteristics (neuroendocrine markers, GM-CSF, vimentin, and the aggressive behaviour) were evident.