Characteristics and treatment of a silent somatotroph tumor that had transformed to a functional type: a case report and literature review.

BACKGROUND

"Functionalization" of silent pituitary neuroendocrine tumors (PitNETs) is a pretty rare clinical phenomenon that reportedly occurs most often with silent corticotroph tumors (SCTs). We report the case of silent somatotroph tumor (SST) that had transformed to functional type. We also review similar cases of SST with functionalization.

CASE DESCRIPTION

A 43-year-old man without suggestive symptoms of a pituitary tumor was referred with a lesion in the sellar region detected incidentally. Serum insulin-like growth factor 1 (IGF-1) (348 ng/mL) was high, whereas growth hormone (GH) was within the normal range. A glucose GH inhibition test showed inhibition of GH to 0.4 ng/mL. Subtotal tumorectomy was performed via a transnasal-sphenoidal approach. Histopathological examination of the operative specimen showed weak expression of GH and diffuse staining of pituitary-specific transcription factor-1 (Pit-1). The final pathological diagnosis was SST. Five years after the first surgery without follow-up, the patient presented again because of headache, impaired vision, bone pain, and high blood glucose concentrations for 2 months. Physical examination showed early acromegalic features. Of interest, greatly increased concentrations of GH (7.2 ng/mL) and IGF-1 (533 ng/mL) were found. Magnetic resonance imaging showed the recurrence of tumor. A diagnosis of acromegaly was considered. The patient underwent a second transsphenoidal pituitary tumor resection, after which his serum GH and IGF-1 concentrations decreased. Unlike the original surgical specimen, immunohistochemical examination of the tissue resected during the second surgery showed strong GH positivity, with similarly strong Pit-1 positivity. The patient was followed up for 6 months without octreotide treatment. At the last follow-up, he was found to have high serum concentrations of GH and IGF-1, which demonstrated another progression of the remnant PitNET. After two courses of octreotide acetate microspheres (20 mg/month), the acromegaly was under control.

CONCLUSIONS

In addition to SCTs, other silent PitNETs could also functionalize. Medical teams of PitNETs should recognize this rare phenomenon and conduct long-term follow-up. After functionalization, these tumors have a high recurrence rate, requiring multiple therapies and long-term follow-up. Further research is essential to determine the mechanism of regulation of secretion of GH by such tumors.