Cellular Classification of Pheochromocytoma and Paraganglioma
Pheochromocytoma and paraganglioma characteristically form small nests of uniform polygonal chromaffin cells (“zellballen”). A diagnosis of malignancy can only be made by identifying tumor deposits in tissues that do not normally contain chromaffin cells (e.g., lymph nodes, liver, bone, lung, and other distant metastatic sites).
Regional or distant metastatic disease is documented on initial pathology in only 3% to 8% of patients; thus, an attempt has been made to identify tumor characteristics associated with future malignant behavior. Pathologic features associated with malignancy include the following:
- Large tumor size.
- Increased number of mitoses.
- DNA aneuploidy.
- Extensive tumor necrosis.
In the absence of clearly documented metastases, no combination of clinical, histopathologic, or biochemical features has been shown to reliably predict the biologic behavior of pheochromocytoma. If no definite malignancy is identified, pathology generally provides insufficient prognostic information regarding the likelihood of recurrence or metastasis. These tumors cannot be considered benign by default; patients require continued lifelong surveillance.[1-7]
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