Summary: Mitotane is used for treatment of advanced adrenocortical carcinoma. It is administered when the carcinoma is unresectable, metastasized, or at high-risk of recurrence after resection. In addition, mitotane is considered to have direct adrenolytic effects. Because of its narrow therapeutic-toxic range, therapeutic drug monitoring (TDM) is warranted. In 2020, a left-sided adrenal gland tumor was found (5.8 cm) in a 38-year-old man. Considering the size of this lesion and inability to exclude an adrenocortical carcinoma on imaging, a laparoscopic adrenalectomy was performed. Histopathologic examination determined presence of an adrenocortical carcinoma (pT2N0M0 ENSAT stadium II; ki67 10-15%). There was no evidence for residual or metastatic disease but given the high risk of recurrence, adjuvant therapy with mitotane was initiated. During TDM, a sudden and spuriously high level of mitotane was observed but without signs or symptoms of toxicity. After exploration, it was found that this high concentration was completely due to uncontrolled hypertriglyceridemia. After correction thereof, mitotane levels were again in the therapeutic range. This observation underscores the importance of TDM sampling in a fasting state with concurrent control of prevalent or incident dyslipidemia.
Learning points: TDM of mitotane is advocated to achieve therapeutic levels while avoiding toxicity. For correct TDM, sampling should be done at least 12 h after last intake of mitotane. Although sampling in fasting conditions in not explicitly mentioned in the guidelines, fasting state should be considered as elevated serum triglyceride levels might cause spuriously high mitotane levels. In patients undergoing treatment with mitotane and presenting with too high or unexplained fluctuating mitotane levels without signs or symptoms of toxicity, hypertriglyceridemia as a possible cause should be investigated. If dyslipidemia occurs in patients under mitotane treatment, other causes than mitotane (e.g. alcohol abuse and diabetes) should be considered and appropriate treatment should be initiated.