Growth hormone-secreting tumor shrinkage after 3 months of octreotide-long-acting release therapy predicts the response at 12 months.

Abstract

The objective of the study was to evaluate whether tumor shrinkage or GH and IGF-I levels achieved after 3 months predicted tumor shrinkage after 12 months of octreotide-long-acting release (LAR) treatment. Patients included 67 patients with de novo acromegaly (33 women, 34 men; aged 20-82 yr) receiving LAR at a dose of 20 mg every 28 d for 3 months. Final LAR dose was 10 mg every 28 d in 4, 30 mg every 28 d in 39, 20 mg every 28 d in 24 patients. The design of the study was analytical, observational, open, and retrospective. Percent change in GH and IGF-I levels and tumor volume after 3 and 12 months of therapy was measured. Stepwise regression and receiving-operator characteristics analysis were used to calculate the optimal cutoff to predict 12 months tumor shrinkage at 12 months. The percent tumor shrinkage after 12 months was significantly correlated with GH, IGF-I, and tumor volume at 3 months and with the dose of LAR administered between 3 and 12 months. There was no correlation with gender, age, baseline GH levels and tumor volume. In a stepwise regression analysis, percent tumor shrinkage after 3 months was the best predictor of tumor shrinkage after 12 months (t = 5.92; P < 0.0001), followed by GH levels after 3 months (t = 2.86; P = 0.0056). To predict 50% or greater tumor shrinkage after 12 months, the best cutoff point of tumor shrinkage at 3 months was 22.1% [sensitivity (95% confidence interval) = 85.5% (71.2-95.4); specificity = 83.3% (65.3-94.3)], whereas that of GH levels after 3 months was 7.8 microg/liter [sensitivity = 70.3% (53.0-84.1); specificity = 93.3% (79.0-99.0)]. Tumor shrinkage achieved after 3 months of LAR treatment at 20 mg/28 d predicted tumor shrinkage at 12 months, provided that dosages were changed according to individual patients requirement.