PRL-R Variants Are Not Only Associated With Prolactinomas But Also With Dopamine Agonist Resistance.

CONTEXT: Knockout prolactin receptor gene (PRL-R) mice are animal models for prolactinomas and PRL acts via autocrine/paracrine inhibiting lactotroph proliferation. Recently, variants of the PRL-R were identified in prolactinoma patients and their frequency was higher compared to individuals from the genomic database. OBJECTIVE: We analyzed PRL-R variants frequency in an extensive cohort of prolactinoma patients and evaluated their association with clinical, laboratorial, and imaging characteristics and hormonal response to cabergoline. DESIGN: Observational, retrospective, and cross-sectional study. SETTING: This study took place at the Neuroendocrinology Unit of Clinics Hospital, Medical School of University of São Paulo, Brazil, a tertiary referral center. PATIENTS AND METHODS: Study participants included adults with sporadic prolactinomas treated with cabergoline, where response to therapy was defined by prolactin normalization with up to 3 mg/week doses. DNA was extracted from blood samples and the PRL-R was analyzed by polymerase chain reaction techniques and automatic sequencing. The association of PRL-R variants with serum prolactin levels, maximal tumor diameter, tumor parasellar invasiveness, and response to cabergoline was analyzed. RESULTS: We found 6 PRL-R variants: p.Ile100(76)Val, p.Ile170(146)Leu, p.Glu400(376)Gln/p.Asn516(492)Ile, p.Glu470Asp e p.Ala591Pro; the last 2 are newly described in prolactinomas' patients. The variants p.Glu400(376)Gln/p.Asn516(492)Ile and p.Ala591Pro were more frequent amongst patients compared to genomic databases, and the p.Asn516(492)Ile showed pathogenic potential using in silico analysis as previously described. PRL-R variants were associated with male sex (P = 0.015), higher serum PRL levels (P = 0.007), larger tumors (P = 0.001), and cabergoline resistance (P < 0.001). CONCLUSIONS: The prolactin/prolactin receptor system seems to be related to prolactinoma tumorigenesis and cabergoline resistance. Additional studies are needed to better understand the PRL-R variants' role and their potential as therapeutic targets.

Survivin: A Potential Marker of Resistance to Somatostatin Receptor Ligands.

CONTEXT: Invasive and somatostatin receptor ligand (SRL)-resistant pituitary tumors represent a challenge in the clinical practice of endocrinologists. Efforts have been made to elucidate reliable makers for both. Survivin and eukaryotic translation initiation factor-binding protein 1 (4EBP1) are upregulated in several cancers and involved in apoptosis and cell proliferation. OBJECTIVE: We explored the role of these markers in somatotropinomas. METHODS: Immunostains for survivin and 4EBP1, and also for somatostatin receptor type 2 (SSTR2), Ki-67, and cytokeratin 18, were analyzed in tissue microarrays containing 52 somatotropinoma samples. Tumor invasiveness was evaluated in all samples while drug resistance was evaluated in 34 patients who received SRL treatment. All these parameters were correlated with first-generation SRL (fg-SRL) responsiveness and tumor invasiveness. RESULTS: Low survivin expression (P = 0.04), hyperintense signal on T2 weighted image (T2WI) (P = 0.01), younger age (P = 0.01), sparsely granular adenomas (SGA) (P = 0.04), high postoperative growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels (P = 0.049 and P < 0.001, respectively), and large postoperative tumor size (P = 0.02) were associated with resistance to fg-SRL. Low survivin and SSTR2 expression and high 4EBP1 expression were associated with SGA (P = 0.04, P = 0.01, and P = 0.001, respectively). Younger age (P = 0.03), large tumor pre- and postoperative (P = 0.04 and P = 0.006, respectively), low SSTR2 expression (P = 0.03), and high baseline GH and IGF-1 (P = 0.01 and P = 0.02, respectively) were associated with tumor invasiveness. However, survivin, 4EBP1, Ki-67, and granulation patterns were not associated with tumor invasion. CONCLUSION: This study suggests that low survivin expression is predictive of resistance to fg-SRL in somatotropinomas, but not of tumor invasiveness.