A 25-year-old woman has a prolactin level of 180 ng/mL, galactorrhoea, and amenorrhoea. MRI shows a 12 mm pituitary tumour with suprasellar extension. Which immunohistochemical marker is MOST expected on biopsy of this tumour?
- A Prolactin (PRL) on cytoplasmic granules of lactotroph cells ✓
- B Growth hormone (GH) with densely granulated eosinophilic cytoplasm
- C Adrenocorticotropin (ACTH) with basophilic cytoplasm and Crooke's hyaline change
- D Thyroid-stimulating hormone (TSH) beta subunit
Correct answer: A. Prolactin (PRL) on cytoplasmic granules of lactotroph cells
Explanation
Prolactinoma is the most common pituitary adenoma (30–40% of all pituitary adenomas); lactotroph adenomas stain positive for prolactin on IHC. Clinically they cause hyperprolactinaemia with galactorrhoea and amenorrhoea in women. Macroadenomas (>10 mm) may cause mass effects including bitemporal hemianopia. Treatment is medical with dopamine agonists (cabergoline, bromocriptine) before surgery.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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