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fetal pulmonary adenocarcinoma

Tuesday 13 September 2011

Definition: Pulmonary fetal adenocarcinomas, formerly referred to as endodermal tumors resembling fetal lung, are considered by some to represent a "monophasic" subset of pulmonary blastoma.

Classical pulmonary blastoma is a biphasic tumor in which fetal adenocarcinoma is accompanied by a primitive mesenchymal component resembling the blastomatous component of renal Wilms tumors.

Regardless of their true histogenesis, fetal adenocarcinomas have a distinctive histologic appearance and are associated with a better prognosis than typical pulmonary adenocarcinomas.

These tumors are composed of relatively bland columnar cells arranged in a complex glandular pattern resembling that seen in the epithelial component of classical pulmonary blastomas and have a striking resemblance to endometrial adenocarcinoma.

The cytoplasm of the columnar cells is often vacuolated and clear due to the presence of glycogen. Stains for epithelial mucins are usually negative, or only focally and faintly positive.

There is often an associated desmoplastic response, although it tends not to be a prominent feature.

Microscopy

- Unencapsulated but well-circumscribed composed of closely packed branching tubules with little intervening stroma resembling fetal lung seen between 10 and 16 weeks’ development (pseudoglandular stage).
- Cribriform arrangements can be prominent and cells arranged in cords and ribbons with peripheral palisading also described.
- The tubules are lined by "endometrioid" nonciliated pseudostratified columnar cells with frequent subnuclear or supranuclear vacuoles.
- Structures resembling squamous morules as in endometrioid adenocarcinoma are often present and the nuclei in these foci often appear optically clear (nuclear pseudoinclusions) due to biotin accumulation.
- Frequent mitoses. Variable necrosis—focal to extensive.
- Low-grade and high-grade variants are recognized which differ significantly in clinical and histopathologic parameters:

  • Low-grade: mean age 34 years, about equal M:F, usually present at early stage, associated with a good prognosis; orderly arrangement of glands, focal necrosis (if present at all), small fairly uniform nuclei with inconspicuous nucleoli, morules common; slight to moderate loose fibromyxoid stroma, neuroendocrine differentiation almost always found, occasional AFP-positive cells, p53 protein overexpression uncommon, nuclear and cytoplasmic β-catenin expression
  • High-grade: mean age 64 years, male predominance, usually advanced stage at presentation, associated with poor prognosis (42% DOD@24 mos.); disorderly arrangement of glands, extensive areas of necrosis common, large pleomorphic nuclei with prominent nucleoli, morules absent, abundant desmoplastic stroma, always AFP-positive cells, p53 overexpression common, membranous β-catenin expression

See also

- pulmonary adenocarcinomas