PLOD1 and neoplasm: Multiple linear regression analysis of serum levels of PRL, E2, FSH, LH, progesterone, testosterone, GH, TSH, and cortisol, tumor volume, and history of disease onset as dependent variables, and the mean GMV of left hippocampus, left OFC, right MFC, and right IFC as independent variables in the prolactinomas group, showed a negative relationship between serum PRL levels and mean GMV of the left hippocampus (p < 0.01) and right IFC (p < 0.05), whereas there was a positive relationship between the mean GMV of the left hippocampus and serum levels of E2 (p < 0.01) and LH (p < 0.05).