Not part of the rule of 10s for pheochromocytomas?

• A. 50% malignant
• B. 10% malignant
• C. 10% bilateral
• D. 10% extraadrenal

Answer: (A)

Pheochromocytomas have historically been described by the rule of 10s, which sums up several approximate proportions: about 10% are malignant, about 10% are bilateral, about 10% are extraadrenal (paragangliomas), and about 10% are familial or occur in children. Because malignancy is around 10%, not 50%, the statement that half of these tumors are malignant does not fit the rule. The other items align with the rule: a 10% malignancy rate, 10% bilateral tumors, and 10% located outside the adrenal gland. So the statement not part of the rule is the one claiming 50% malignant.