Predictors of tumor shrinkage after primary therapy with somatostatin analogs in acromegaly: A prospective study in 99 patients

Context: Primary treatment with depot octreotide and lanreotide induces tumor shrinkage in newly diagnosed patients with acromegaly. Objective: The objective of the study was to evaluate clinical predictors of tumor shrinkage. Design: This was an analytical, observational, open, prospective study. Subjects: The study included 99 patients: 13 with microadenoma and 86 with macroadenoma (25 enclosed, 32 extrasellar, 29 invasive). Main Outcome Measures: Age, gender, estimated disease duration, body mass index, GH and IGF-I levels, and tumor volume at diagnosis and after 12 months of treatment were measured. Percentage of GH, IGF-I, and tumor size changes from baseline were also analyzed. Tumor changes were scored as absent (+/- 0-25%), mild (+/- 25.1-50%), moderate (+/- 50.1-75%), or notable (75%). Interventions: Sixty patients (60.6%) received depot octreotide im (20-30 mg every 28 d), and 39 patients (39.4%) received lanreotide im (60-90 mg every 28 d). Results: Basal tumor volume and maximal tumor diameter correlated with age, disease duration, and GH levels. After 12 months, GH levels were controlled ( <= 2.5 mu g/liter) in 57.6%, IGF-I levels in 45.5%, and both in 42.4%. Shrinkage was absent in 22 patients (22.2%), mild in 31 (31.1%), moderate in 30 (30.3%), and notable in 14 patients (14.1%). Two patients ( not responding to treatment) had a mild tumor increase ( by 34 and 31.2%, respectively). Basal and posttreatment tumor volumes were highly correlated (r = 0.79, P < 0.0001). At the multistep regression analysis, the percent IGF-I decrease (t = 2.6; P = 0.011) was the best predictor of posttreatment tumor volume, followed by patients' age (t = 2.1; P = 0.042) and percent GH decrease (t = 2.0; P = 0.044). Conclusions: Most patients with acromegaly (75.5%) had 25% or greater tumor shrinkage after 12 months of primary somatostatin analog therapy: significant increase of tumor mass occurred in only 2.1% of patients (uncontrolled during treatment). Best predictor of tumor shrinkage was posttreatment IGF-I.