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 PCR 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 six 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 two 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 PRL/PRL-R 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.

Aos meus pais, Patrícia e Eduardo, que me conduziram e me deram as bases para chegar até aqui. À minha irmã, Amanda, que sempre foi minha maior incentivadora e melhor amiga. Ao meu cunhado, Leonardo, que pude contar como um mentor e irmão. Ao Carlos Augusto, que esteve ao meu lado me apoiando e me ajudou em cada detalhe com paciência e carinho.