Adrenal oncocytic phaeochromocytoma with putative adverse histologic features: a unique case report and review of the literature.

Oncocytic phaeochromocytomas are exceedingly rare tumours. To date, there are three reported cases in the literature. This report describes a case of adrenal oncocytic phaeochromocytoma with unique features and malignant potential in a 68-year-old man. The patient presented with an incidental non-functional mass discovered on routine radiological investigation, which was subsequently excised. Histologically, the tumour cells showed oncocytic features with high-grade nuclear abnormalities and foci of extension to the peri-adrenal fat. Immunohistochemistry performed was positive for chromogranin, CD56, S-100 and p53 and negative for inhibin, HMB-45, EMA, AE1/AE3, Cam 5.2 and calretinin. Electron microscopy showed electron dense granules of neurosecretory type, which confirmed the diagnosis. The malignant potential of the tumour was assessed on available histologic scoring systems, which demonstrated a high malignant potential. However, no recurrence was detected after 5 years of follow-up. Compared to all the previously reported cases of oncocytic phaeochromocytoma, this patient was the oldest on presentation, was the only case with identified high malignant potential and has the longest follow-up. A review of the literature showed that all the oncocytic phaeochromocytomas reported were non-functional, non-metastasizing and were described in women. To conclude, oncocytic phaeochromocytoma should be in the differential diagnoses of oncocytic tumours of the adrenal gland. Additional studies are needed to predict the behaviour of this entity.