Fetal adenocarcinoma of the lung

Fetal adenocarcinoma of the lung (FLAC) is a rare form of adenocarcinoma of lung (falls under invasive category).

Epidemiology

Some reports suggest its occurence at ~0.1%-0.5% of all pulmonary neoplasms. Despite its "fetal" tissue morphology it typically presents in middle aged to elderly patients (60 to 70 year olds)

Pathology

It is an adenocarcinoma resembling developing fetal lung in its pseudoglandular stage (i.e. that seen at 8-16 weeks of gestation). It is considered different from a pulmonary blastoma due to a lack of a mesenchymal component

Fetal adenocarcinoma of the lung can be divided into two forms according to severity.

low-grade fetal adenocarcinoma (L-FLAC): low nuclear atypia and prominent morule formation and has a pure pattern
high-grade fetal adenocarcinoma (H-FLAC): often over 50% fetal morphology, and often associated with other conventional types of lung adenocarcinoma

Markers

Serum markers

alpha-fetoprotein (AFP): thought to be elevated in most cases

Tissue/immune markers

TTF1: usually positive
KRAS mutation: most tumors negative
EGFR mutation: most tumors negative

History and etymology

It is thought to have been first described by WG Barnard in 1945 and 1952, as a biphasic tumor comprising an epithelial component surrounded by mesenchymal stroma resembling fetal lung, hence initially named as “embryoma of the lung".