As ErbB signaling is a determinant of prolactin synthesis, role of ErbB receptors was tested for prolactinoma outcomes and therapy. The objective of this study was to characterize ErbB receptor expression in prolacti-nomas and then perform a pilot study treating resistant prolactinomas with a targeted tyrosine kinase inhibitor (TKI). Retrospective analysis of prolactinomas and pilot study for dopamine agonist resistant prolactinomas in tertiary referral center. We performed immunofluorescent staining of a tissue array of 29 resected prolactinoma tissues for EGFR, ErbB2, ErbB3, and ErbB4 correlated with clinical features. Two patients with aggressive resistant prolactinomas enrolled and completed trial. They received lapatinib 1,250 mg daily for 6 months with tumor and hormone assessments. Main outcome measures were positive tumor staining of respective ErbB receptors,therapeutic reduction of prolactin levels and tumor shrinkage. Treated PRL levels and tumor volumes were suppressed in both subjects treated with TKI. EGFR expression was positive in 82 of adenomas, ErbB2 in 92 , ErbB3 in 25 , and ErbB4 in 71 , with ErbB2 score > EGFR > ErbB4 > ErbB3. Higher ErbB3 expression was associated with optic chiasm compression (p — 0.03), suprasellar extension (p = 0.04), and carotid artery encasement (p — 0.01). Higher DA response rates were observed in tumors with higher ErbB3 expression. Prolactinoma- expression of specific ErbB receptors is associated with tumor invasion, symptoms, and response to dopamine agonists. Targeting ErbB receptors may be effective therapy in patients with resistant prolactinomas.
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