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

Objective: 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: 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. Design: The design of the study was analytical, observational, open, and retrospective. Outcome Measures: 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. Results: 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 mu g/liter [sensitivity = 70.3% (53.0-84.1); specificity = 93.3% (79.0-99.0)]. Conclusion: 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.