PRL and neoplasm: Similar results were obtained by Vermeulen et al. The authors investigated the possible predictive factors of DA-resistance in a group of 69 patients and found that male gender, large tumour volume, prolonged time to prolactin normalisation, and the presence of cystic, haemorrhagic, and/or necrotic components on MRI scans (before the start of pharmacological treatment) were the most significant predictors.