Case 69

A 45-year-old female with a large lung mass measuring 12.5 cm.

1. If the cells observed that are positive for both EMA and TTF-1, negative for CD34, what's your diagnosis?

   A: Adenocarcinoma

   B: Solitary fibrous tumor

   C: Pecoma

   D: Sclerosing pneumocytoma

   E: Carcinoid tumor

Answer

The correct answer is D.

Key Features:

• Composed of two neoplastic cell types:

  • Cuboidal surface cells resembling type II pneumocytes.

  • Round stromal cells with bland nuclei, fine chromatin, and scant nucleoli.

• Four growth patterns:

  • Papillary: Surface cells cover round cells, without true fibrovascular cores.

  • Sclerotic: Fibrosis with hyalinized collagen, inflammatory cells, haemosiderin, calcification, and ossification.

  • Solid: Sheets of round cells with possible tubular/adenoid structures.

  • Haemorrhagic: Large blood-filled spaces lined by cuboidal cells.

Diagnostic Pitfalls:

• Multinucleated giant cells from surface cell fusion.

• Sclerotic papillae replacing round cells with collagen.

• Delicate papillary structures mimicking true papillae.

• Round cells with spindle or signet-ring morphology.

• Myxoid matrix surrounding round cell cords.

Immunohistochemistry:

• Both cell types: EMA+, TTF1+

• Surface cells: CK7+, Pancytokeratin+, CAM5.2+, Napsin A+ (diffuse)

• Round cells: Weak/negative for epithelial markers

• Neuroendocrine markers: Negative

• ER/PR positivity: Reported in some round cells

2. Do you know the molecular findings that alway present in this diagnosis?

   A: ALK

   B: ATK-1

   C: B-catenin

   D: ESR1

   F: AKT-1

   
   

Answer

AKT1 alterations are present in nearly all sclerosing pneumocytomas and may be useful for diagnosis in selected cases.

Reference: https://tumourclassification.iarc.who.int/chaptercontent/35/11

Case credit: https://qp.91360.com/27.html?lang=en

Author: Wangpan Jackson Shi, MD