Should a 4.2 mm adrenal tumor be removed?

It depends.: First of all, I am assuming you mean a 4.2 centimeter tumor. If so, the first issue is to determine if this tumor is "functional", meaning that it secretes abnormal amounts of normal substances such as Epinephrine or steroids. If it is not functional, most people will watch tumors less than 4 CM and remove those larger than 6cm; the decision for those 4-6cm is often based on one's age and health.

No unless: Unless it's hornonally active in which surgical excision is an option. Keep in mind that most adrenal nodules of this size ate benign and "non" secretors that only need serial imaging to ensure the size remains stable.