A pituitary tumor from a 35-year-old man with acromegaly is composed of weakly acidophilic cells with prominent paranuclear round eosinophilic globules that stain strongly with low molecular weight cytokeratin (CAM5.2). Compared with densely granulated somatotroph tumors, this subtype responds less well to first generation somatostatin analogs. Identify the subtype.

• A Densely granulated somatotroph adenoma
• B Mammosomatotroph adenoma
• C Plurihormonal Pit-1 positive adenoma
• D Sparsely granulated somatotroph adenoma ✓

Explanation

Sparsely granulated somatotroph adenoma is defined by the presence of fibrous bodies, which are spherical paranuclear accumulations of intermediate filaments of keratin 8 and 18 highlighted by CAM5.2 immunostain. These tumors show weaker and patchy growth hormone staining, express alpha subunit less often, grow faster, and respond poorly to octreotide compared with densely granulated somatotroph adenomas. Mammosomatotroph tumors coexpress prolactin, and plurihormonal Pit-1 tumors require expression of additional Pit-1 lineage hormones.

Reference: WHO Classification of Endocrine and Neuroendocrine Tumours, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.