— pulmonary endodermal tumour or adenocarcinoma of fetal type. Young patients with a solitary mass, endometrioid type glands and better prognosis.

— pulmonary blastoma: adults, peripheral, solitary and large. Well-differentiated fetal-type tubular glands in a cellular embryonal stroma and poor prognosis.

— carcinosarcoma/sarcomatoid carcinoma: pulmonary or polypoid bronchial mass. Squamous (or large cell/adenocarcinoma) with fibrosarcoma-like spindle cells (diffuse or focal cytokeratin (AE1/AE3) positive) representing monophasic sarcomatoid (spindle cell carcinoma), or biphasic with heterologous mesenchymal differentiation, e.g. cartilage, bone, striated muscle. Poor prognosis and overlaps with pleomorphic (spindle/giant cell) carcinoma. Metastases can be epithelial, sarcomatoid or mixed.

Note that only about 40% of primary lung carcinomas are of homogeneous histological type and mixed differentiation and patterns are reasonably common, e.g. squamous and small cell components, acinar and papillary adenocarcinoma.

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