A 52-year-old man presented with cerebrospinal fluid rhinorrhea and was found to have an invasive 4.2-cm pituitary mass with only modestly elevated serum prolactin. Additional imaging detected a mediastinal mass suspicious for a thoracic paraganglioma. Biochemical screening demonstrated marked elevations of plasma and urinary dopamine, supporting the diagnosis of a dopamine-secreting paraganglioma. The clinical course and diagnostic workup were reported in JCEM Case Reports and presented at ENDO 2026.
The patient initially sought care for cerebrospinal fluid rhinorrhea, which prompted neuroimaging and identification of the large invasive pituitary lesion. The pituitary mass measured 4.2 cm and, by size alone, would typically be associated with substantially higher prolactin concentrations. However, the measured prolactin was only modestly elevated, prompting consideration of alternative explanations, including a poorly functional prolactinoma, a less differentiated PIT-1–lineage adenoma, or a nonfunctional sellar mass.
Further imaging identified a mediastinal mass concerning for a thoracic paraganglioma. The combination of a large pituitary lesion and an extra-adrenal neuroendocrine mass raised the possibility of multiple endocrine neoplasia or a syndromic association.
Biochemical testing revealed marked increases in plasma and urinary dopamine, consistent with a functioning dopamine-secreting paraganglioma. The relatively low initial prolactin in the setting of a large pituitary tumor was notable; authors interpret this discordance as evidence that circulating dopamine from the paraganglioma exerted tonic inhibition on prolactin secretion from the pituitary adenoma.
Two weeks after surgical removal of the mediastinal paraganglioma, the patient’s prolactin level rose approximately six-fold, supporting the hypothesis that endogenous dopamine production had been suppressing pituitary prolactin secretion. This temporal relationship was central to the case’s interpretation as biochemical crosstalk between two distinct endocrine tumors.
The mediastinal tumor was resected, and its biochemical profile and clinical behavior were consistent with a dopamine-secreting paraganglioma. Following paraganglioma removal, the pituitary lesion was surgically resected by neurosurgeons. Histopathology of the pituitary tumor demonstrated PIT-1 positivity but lacked staining for expected lineage hormones, including prolactin, despite the clinical diagnosis of a prolactinoma. The authors considered this most consistent with an immature PIT-1–lineage pituitary adenoma, a rare subtype that can be less differentiated, larger, and more aggressive with variable hormone staining.
Prolactin-secreting pituitary adenomas are typically inhibited by dopamine and often treated pharmacologically with dopamine agonists to reduce prolactin secretion and tumor size. In this patient, endogenous dopamine secreted by the paraganglioma likely provided continuous dopaminergic inhibition of the pituitary tumor, masking the expected hyperprolactinemia. Removal of the dopamine source unmasked robust prolactin hypersecretion, demonstrating direct endocrine interaction between two independent tumors. The authors describe this as an example of endogenous pharmacotherapy and highlight that biochemical crosstalk between coexisting tumors is not well characterized in the literature.
Given the occurrence of multiple endocrine tumors, the team performed germline genetic testing. Results identified an SDHC variant of uncertain significance (VUS). The authors note that the VUS did not establish a definitive hereditary diagnosis in this case. They emphasize that genetic testing is important for all patients with pheochromocytoma or paraganglioma and particularly relevant when multiple endocrine tumors are present, because a pathogenic variant, when found, has implications for long-term surveillance and family member risk assessment.
After paraganglioma resection and the subsequent rise in prolactin, the patient elected to continue medical therapy with cabergoline to suppress prolactin and reduce the residual pituitary tumor rather than undergo radiation therapy. At the time of reporting, the patient was asymptomatic on cabergoline. The authors discuss that cabergoline was used to maintain prolactin suppression and attempt tumor shrinkage.
The case underscores several clinical points: dopamine-secreting paragangliomas can be clinically subtle and may not produce classic catecholamine excess symptoms; biochemical interactions between separate endocrine neoplasms can mask expected hormone profiles and complicate diagnosis; and unusual presentations should prompt thorough biochemical screening and consideration of genetic evaluation. The authors also highlight that immature PIT-1–lineage pituitary adenomas may show discordant immunohistochemical staining relative to clinical hormone production, complicating histopathologic interpretation.
The case was published in JCEM Case Reports and presented by lead author Tamaryn Fox, MD, at ENDO 2026 in Chicago during a session highlighting clinical pearls from JCEM Case Reports. William F. Young, MD, commented on the case as an instructive example of endogenous pharmacotherapy when one endocrine neoplasm functionally treats another. The authors and presenters emphasized the educational value of rare, well-documented cases for understanding physiology, diagnosis, and management of complex endocrine disease.