Treatment with octreotide LAR in clinically non-functioning pituitary adenoma: results from a case-control study

Surgical cure cannot be achieved in most patients with invasive non-functioning pituitary macroadenoma (NFPA). Short-term residual tumor treatment with somatostatin analogs has produced disappointing results. This prospective case-control study assessed the efficacy of chronic treatment with long acting octreotide (octreotide LAR) on tumor volume in patients harboring post-surgical NFPA residue. The study population comprised 39 patients with NFPAs not cured by surgery. All patients underwent somatostatin receptor scintigraphy at least 6 months after the last surgery. Patients with a positive pituitary level octreoscan at (n = 26) received octreotide LAR (20 mg every 28 days) for ≥ 12 months (mean follow-up 37 ± 18 months) (Treated group). Moreover, a fragment of tumor tissue from patients in the treated group was retrospectively collected to assess the immunohistochemical expression of somatostatin receptor subtypes (SSTRs). The patients with a negative octreoscan (n = 13) formed the control group (mean follow-up 37 ± 16 months). Hormonal, radiological and visual field parameters were periodically assessed. In the treated group, all tumors expressed at least one SSTR subtype. The SSTR5 subtype was the most abundant, followed by SSTR3. The tumor residue increased in five of 26 patients (19%) in the treated group and in seven of 13 controls (53%). Visual field and pituitary function did not change in any patient. This study indicates that SSTR5 and SSTR3 are the most frequently expressed SSTR subtypes in NFPAs and supports a potential role of SSTR subtypes in stabilization of tumor remnant from NFPAs.