ABSTRACT
Malignant cells have the ability to insinuate themselves between adjacent normal cells and invade the surrounding connective tissues. For epithelial tumours, the step is for the tumour cells to breach the basement membrane, i.e. to proceed from the stage of intraepithelial neoplasia to that of an invasive tumour. The tumour had involved the parietal pleura and the lymph node metastases suspected on gross examination were confirmed histopathologically. Tumours are further classified according to the cell type that they resemble, i.e. their differentiation. This property is usually determined by the tumour's appearance on light microscopy, i.e. its morphological phenotype. Adenomas are benign tumours of glandular epithelium. The tumour cells in such a tumour form glandular structures mimicking the arrangement of the normal tissue. Small cell carcinoma is a tumour that shows neuroendocrine differentiation in the form of neurosecretory granules which may be found on electron microscopy or immunostaining for vesicle membrane proteins such as synaptophysin.
