Pulmonary adenocarcinomas of the fetal lung type: a clinicopathologic study indicating differences in histology, epidemiology, and natural history of low-grade and high-grade forms.

Seven cases of high-grade adenocarcinoma of fetal lung type (H-FLAC) are compared with nine cases of pulmonary endodermal tumor resembling fetal lung or low-grade adenocarcinoma of fetal lung type (L-FLAC). Of the seven patients with of H-FLAC, four were men and three were women. All of the patients but one were in their 60s or 70s. Five patients were smokers. After resection of the tumor, three patients died of metastases, two patients are alive with no evidence of disease, and two patients died of a postoperative complication. Histologically, H-FLAC and L-FLAC have both complex glandular structures resembling fetal lung and neuroendocrine differentiation. Two cases of H-FLAC had stromal proliferation typical of biphasic pulmonary blastoma. The H-FLAC was distinguished from L-FLAC by the presence of disorganized glands, large vesicular nuclei, prominent nucleoli, pronounced anisonucleosis, absence of morules, transition to conventional adenocarcinoma, broad areas of necrosis, desmoplastic stroma, overexpression of p53 protein, and production of alpha-fetoprotein. High and low grades of FLAC explain discrepancies in previously reported clinicopathologic features of FLAC. The H-FLAC needs to be distinguished from L-FLAC. Both forms may have stromal components, so both have been referred to as blastomas. The H-FLAC represents the prototype of so-called pulmonary blastoma predominantly seen in the elderly, whereas L-FLAC and its biphasic form predominate in the middle-aged population.