Percent reduction of growth hormone levels correlates closely with percent resected tumor volume in acromegaly

OBJECT Correlation between tumor volume and hormone levels in individual patients would permit calculation of the fraction of tumor removed by surgery, by measuring postoperative hormone levels. The goals of this study were to examine the relationship between tumor volume, growth hormone (GH), and insulin-like growth factor-1 (IGF-1) levels, and to assess the correlation between percent tumor removal and the reduction in plasma GH and IGF-1 in patients with acromegaly. METHODS The 3D region of interest based volumetric method was used to measure tumor volume via MRI before and after surgery in 11 patients with OH-secreting adenomas. The volume of residual tumor as a fraction of preoperative tumor volume was correlated with OH levels before and after surgery. Examination of this potential correlation required selection of patients with acromegaly who 1) had incomplete tumor removal, 2) had precise measurements of initial and residual tumor, and 3) were not on medical therapy. RESULTS Densely granulated tumors produced more peripheral OH per mass of tumor than sparsely granulated tumors (p = 0.04). There was a correlation between OH and IGF-1 levels (p = 0.001). Although there was no close correlation between tumor size and peripheral OH levels, after normalizing each tumor to its own plasma OH level and tumor volume, a comparison of percent tumor resection with percent drop in plasma OH yielded a high correlation coefficient (p = 0.006). CONCLUSIONS. Densely granulated somatotropinomas produce more OH per mass of tumor than do sparsely granulated tumors. Each OH-secreting tumor has its own intrinsic level of OH production per mass of tumor, which is homogeneous over the tumor mass, and which varies greatly between tumors. In most patients the fraction of a OH-secreting tumor removed by surgery can be accurately estimated by simply comparing plasma OH levels after surgery to those before surgery.