Somatostatin analogs have been shown to be effective for the treatment of TSH-secreting
pituitary adenomas. However, their use in this indication is limited by the fact that available analogs require several daily sc
injections. The present study was performed to evaluate the effects of a
slow release formulation of the
somatostatin analog
lanreotide (SR-L) on both
hormone secretion and
tumor size and to assess the tolerance in a series of thyrotropinomas treated for 6 months. Eighteen patients with
hyperthyroidism related to a TSH-secreting
pituitary adenoma, evidenced by pituitary magnetic resonance imaging, were studied. After a basal assessment, each patient received 30 mg SR-L, im, every 14 days for 1 month. Then, according to the free T3 (fT3) plasma level measured, 9 of 18 patients were injected twice monthly, and 7 of 18 patients received SR-L every 10 days for 5 additional months. One patient was dismissed from the study in month 1 of the study for side-effects and another in month 3 for noncompliance to the protocol. Clinical and
biological evaluations (plasma TSH, free alpha-subunit, fT4, fT3, and
lanreotide levels) were performed before and in months 1, 3, and 6 of treatment. Pituitary magnetic resonance imaging and gallbladder ultrasonography were performed both at entry and at the end of the study. Clinical signs of
hyperthyroidism improved within 1 month in all 16 evaluable patients. Mean (+/- SEM) plasma
lanreotide levels reached 1.11 +/- 0.43 and 1.69 +/- 0.65 ng/mL in month 3 using 2 and 3
injections/month, respectively, then remained stable until the end of the study. During
therapy, the plasma TSH level decreased from 2.72 +/- 0.32 to 1.89 +/-0.27 mU/L (P < 0.01), with parallel significant changes in free alpha-subunit. During the same period, plasma fT4 and fT3 levels decreased from 37.9 +/- 2.9 to 19.7 +/- 2.3 pmol/L (P < 0.01) and from 14.6 +/- 1.1 to 8.3 +/- 0.8 pmol/L (P < 0.01), respectively. No statistically significant change in mean
adenoma size was observed after 6 months of treatment. Side-effects, including
pain at the injection point,
abdominal cramps, and
diarrhea, were mild and transient and did not lead to interruption of the treatment. No
gallstones occurred during the study. SR-L appears to be able to suppress clinical signs of
hyperthyroidism in our series of patients with TSH-secreting
pituitary adenomas. The analog also reduces plasma TSH and
thyroid hormone levels, which were normalized in 13 of 16 cases. The effect was maintained throughout the treatment using 2 or 3 SR-L
injections monthly without any problem of tolerance. We conclude that SR-L is a safe and effective treatment of thyrotropinomas and avoids the drawbacks of the modes of administration of other
somatostatin analogs, given three times daily.