 primari epidermoid cancer lung ultrastructur studi earli epidermoid epithelioma human lung initi prolifer bodi cell structur analog medium cell modif basal cell normal bronchial wall presenc desmosom tonofibril cell stratum germinativum bronchial epithelium cell deriv allow better understand malpighian metaplasi wall account epidermoid evolut bronchial epithelioma nuclear cytoplasm modif possibl causal viru 