SAT-272 Pituitary Macroadenoma Co-Secreting TSH and PRL Responsive to Cabergoline

Background: Thyroid-stimulating hormone (TSH) secreting tumors (TSHoma) account for 0.5-2% of all pituitary adenomas with a prevalence of 1-2 cases per million, indicating that TSHomas are very rare. The majority of TSHomas solely secrete TSH however 9.7% co-secrete Prolactin (PRL). We are reporting a case of co-secreting TSH and PRL pituitary macroadenoma responsive to Cabergoline (CAB) Case: A 52 year old multiparous female presented with symptoms of galactorrhea and amenorrhea. Lab investigation revealed elevated PRL 73 ng/mL (n [normal] = 1-24), Total T3 305 ng/dL (n = 71-180), Free T4 (FT4) 2.37 ng/dL (n = 0.6-1.15), TSH 6.09 UIU/mL (n = 0.5-5.0), and α subunit 7.7 ng/mL. Estradiol was low at 16.9 pg/mL and FSH 6.3 MIU/mL LH 1.7 MIU/mL. Visual field testing showed a right nasal step. MRI imaging demonstrated a 21x24x32mm pituitary macroadenoma with optic chiasm distortion. Partial Transsphenoidal surgery (TSS) was performed and immunostaining of tumor tissue was positive for PRL and negative for other pituitary hormones. One month post-surgical MRI revealed 14x17x15mm residual tumor. One month post-op TFTs were normal: TSH 0.99 ng/dL, FT4 0.61 ng/dL; PRL decreased to 34.8 ng/mL. Six month post-op TSH increased to 5.86 UIU/mL, FT4 1.43 ng/dL, and PRL 44.7 ng/mL. Two years post-op TSH 8.06 ng/dL with elevated α subunit 3.4 ng/mL and PRL 56.8 ng/mL. Octreotide was then initiated for TSHoma treatment however she was unable to tolerate the medication due to diarrhea so was switched to CAB. After starting CAB at 0.5mg twice a week, residual sellar mass increased in size to 19.5x16x23mm with TFTs: TSH 5.66 UIU/mL, FT4 2.48 ng/dL. CAB dose was eventually uptitrated to 1mg twice a week. Repeat MRI showed slight decrease in pituitary lesion to 19x21x18mm and downtrending TFTs: TSH 2.28 UIU/mL, FT4 1.17 ng/dL. Discussion: In patients with pituitary tumors associated with elevated PRL and TSH, TSHoma should be part of the differential diagnosis. This patient’s initial lab evaluation with elevated PRL, TSH, FT4, Total T3, and α subunit confirm the diagnosis of a pituitary macroadenoma with co-secretion of PRL and TSH. Elevated PRL, TSH, FT4 and α subunit levels occurred 6 months after partial TSS resection with growing tumor size eventually requiring medical therapy. On CAB therapy, there were reductions in PRL, TSH, and FT4 levels as well as a decrease tumor size. This is the first reported case of a TSHoma responsive to CAB.