Surgical specimens of 64 adrenal PCCs were investigated by conventional histology, immunocytochemistry and DNA-cytophotometry. Tumour weights of more than 200 g were recorded for each of the 6 malignant, but for only one of the 58 clinically benign neoplasms. Increased mitotic activity (greater than 5 mitoses/10 HPF) was, apart from one benign lesion, only seen among malignomas. Immunocytochemically, all malignomas were entirely devoid of S100-positive sustentacular cells and, as compared to benign PCCs, showed reduced expression rates of different neuropeptides. Upon cytophotometry, only 5/43 tumours exhibited euploid DNA histograms, all these cases belonging to the group of benign PCC. According to these findings, morphology does not enable a definite prediction of the clinical course of individual PCC cases, but renders the definition of risk groups possible. A benign diagnosis can be made in multihormonal euploid tumours weighing less than 200 g. In larger neoplasms and in cases lacking sustentacular cells and showing increased mitotic activity, an unfavourable prognosis is to be suspected and the same therapeutic procedures should be applied as for tumours in which malignancy is evident in metastatic growth.
