Predictive factors for responses to primary medical treatment with lanreotide autogel 120 mg in acromegaly: post hoc analyses from the PRIMARYS study

Purpose PRIMARYS (NCT00690898) was a 48-week, open-label, phase 3b study, evaluating treatment with the somatostatin receptor ligand lanreotide autogel (stable dose: 120 mg/28 days) in treatment-naive patients with growth hormone (GH)-secreting pituitary macroadenoma. This post hoc analysis aimed to evaluate factors predictive of long-term responses. Methods Potential predictive factors evaluated were: sex, age, and body mass index at baseline; and GH, insulin-like growth factor-1 (IGF-1), and tumor volume (TV) at baseline and week 12, using univariate regression analyses. Treatment responses were defined as hormonal control (GH <= 2.5 mu g/L and age- and sex-normalized IGF-1), tight hormonal control (GH < 1.0 mu g/L and normalized IGF-1), or >= 20% TV reduction (TVR). Receiver-operating-characteristic (ROC) curves were constructed using predictive factors significant in univariate analyses. Cut-off values for predicting treatment responses at 12 months were derived by maximizing the Youden index (J). Results At baseline, older age, female sex, and lower IGF-1 levels were associated with an increased probability of achieving long-term hormonal control. ROC area-under-the curve (AUC) values for hormonal control were high for week-12 GH and IGF-1 levels (0.87 and 0.93, respectively); associated cut-off values were 1.19 mu g/L and 110% of the upper limit of normal (ULN), respectively. Results were similar for tight hormonal control (AUC values: 0.92 [GH] and 0.87 [IGF-1]; cut-off values: 1.11 mu g/L and 125% ULN, respectively). AUC and J values associated with TVR were low. Conclusions The use of predictive factors at baseline and week 12 of treatment could inform clinical expectations of the long-term efficacy of lanreotide autogel.