PULMONARY ADENOCARCINOMAS OF THE FETAL LUNG TYPE - A CLINICOPATHOLOGICAL 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) a re compared with nine cases of pulmonary endodermal tumor resembling f etal 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 w ere smokers. After resection of the tumor, three patients died of meta stases, two patients are alive with no evidence of disease, and two pa tients died of a postoperative complication. Histologically, H-FLAC an d L-FLAC have both complex glandular structures resembling fetal lung and neuroendocrine differentiation. Two cases of H-FLAC had stromal pr oliferation typical of biphasic pulmonary blastoma. The H-FLAC was dis tinguished from L-FLAC by the presence of disorganized glands, large v esicular nuclei, prominent nucleoli, pronounced aniso-nucleosis, absen ce of morules, transition to conventional adenocarcinoma, broad areas of necrosis, desmoplastic stroma, overexpression of p53 protein, and p roduction of alpha-fetoprotein. High and low grades of FLAG explain di screpancies in previously reported clinicopathologic features of FLAG. 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 predomi nantly seen in the elderly, whereas L-FLAC and its biphasic form predo minate in the middle-aged population.