Aims: The malignancy of phaeochromocytomas is difficult to predict. Traditionally, only a metastasized tumour is considered malignant. The aim of this study was to assess the histopathological and clinical features, as well as the proliferative activity, and to analyse p53 and p21 expression in 105 phaeochromocytomas.
Methods and results: All malignant phaeochromocytomas (n = 8) showed at least one of the histologically suspicious features, i.e. over five mitoses/10 high-power fields, necrosis, capsular or vascular invasion. Malignant tumours were larger, but the age and gender of the patients were not significantly different. All benign (n = 33) and most of the borderline (18/21) adrenal phaeochromocytomas had less than 6% Ki67+ tumour cells, while most malignant tumours (6/7) expressed Ki67 in >6% of the cells. p53+ immunohistochemistry was found in two malignant tumours, while p21 expression did not correlate with malignancy.
Conclusions: These data suggest that the lack of histologically suspicious features, low proliferative activity, smaller size, and negative p53 immunostaining point to a benign diagnosis in phaeochromocytomas.