Fetal adenocarcinoma

Fetal adenocarcinoma (FA) of the lung is a rare subtype of pulmonary adenocarcinoma that exhibits tissue architecture and cell characteristics that resemble fetal lung tissue upon microscopic examination. It is currently considered a variant of solid adenocarcinoma with mucin production. FA can produce repeated hemoptysis, possibly related to cavitation of the tumor. Other presenting symptoms described have included: flu-like syndrome with cough and fever, Due to its rarity, little is known of the genetics of FA. One small series of 6 cases showed that MDM2 protein was expressed in 5 of them (83%), and p53 protein was overexpressed in 50%. However, a larger series of 12 cases revealed no p53 gene mutations. The details of the histogenesis of FA remain unknown and highly debated. Adenocarcinomas are most often highly heterogeneous peripheral tumors, and are thought to arise from malignant transformation of primitive cells that can exhibit differentiation characteristics of Club cells, Type II pneumocytes, bronchiolar surface cells, bronchial gland cells, or goblet cells. Most FA's are well or moderately differentiated tumors, although high-grade, poorly differentiated variants have been described. Tissue resembling FA can also be found admixed with a component made up of primitive blastoma-like cells. In such cases, these biphasic tumors are classified as a form of pulmonary blastoma because the presence of the blastomatous cells dramatically worsens the prognosis. FA can occur in combination with other forms of lung cancer, particularly other variants of adenocarcinoma. There also seems to be an association with clear cell lung cancer variants. A case of combined small cell lung carcinoma featuring components of FA and cells resembling those from carcinoid tumor has been reported, illustrating the unique complexity and heterogeneity of divergent histogenesis and cell differentiation in lung cancer.