THU609 Timeline For Undetectable Mitotane Plasma Levels In Adrenocortical Carcinoma Patients After Stopping Treatment

Disclosure: N. Younes: None. P. Hétu: None. A. Lacroix: None. I. Bourdeau: None. Background: Mitotane (o,p’DDD) is an adrenolytic steroidogenesis inhibitor recommended in the treatment of adrenocortical carcinoma (ACC) with a high risk of recurrence. Mitotane has a long plasma elimination half-life, because of its highly lipophilic properties. Objectives: To further explore time to reach undetectable mitotane plasma levels (UM) in treated ACC patients after stopping the medication. Methods: We retrospectively analyzed the medical files of 13 adult patients with ACC who were treated with mitotane during at least 24 months, between 2006 and 2020, in our center. We calculated the duration in months for plasma concentrations of mitotane to be undetectable, from the time of cessation of mitotane in all 13 patients. Baseline demographic characteristics of patients and baseline tumor characteristics were recorded, along with the maximal dose of mitotane used. We also explored the time it took patients to be able to stop glucocorticoid and/or mineralocorticoid replacement therapy following mitotane cessation. Results: The mean age at diagnosis of ACC was 48.2 ± 14.9 years and 69.2% of patients were female. Patients weighted 78.2 ± 27.2 Kg. The mean tumor size and proliferation index Ki67 were 8.1 ± 4.3 cm and 13.3 ± 7.3%. None of the patients had metastasis at diagnosis. They were treated with a mean of 4 ± 2 g of mitotane daily, for 33.5 ± 9 months. Only one patient never had documented therapeutic mitotane range (between 14 and 20 mg/L) during treatment. The time to UM from the time of mitotane cessation was 13.2 ± 7.1 months. All 13 patients were taking glucocorticoid replacement therapy and 5 were able to completely withdraw hydrocortisone 39 ± 14.5 months after stopping mitotane treatment. Only 2 patients out of the 6 patients that were on mineralocorticoid replacement therapy, were able to stop after 34.2 and 59.7 months, respectively. There was no significant relationship found between the duration of exposure to mitotane and the time to UM (p=0.82). On simple linear regression, patients’ weight explained 80% of variance of time to UM. There was a positive relationship between patients’ weight and time to UM (standardized coefficient beta 0.89, p <0.0001). On multiple linear regression, patients’ weight was an independent predictor of time to UM. Conclusion: Mitotane can take up to 13 months to become undetectable in patients’ plasma after cessation. In our cohort, it is mainly influenced by increased weight but not by duration of exposure to the drug. Presentation: Thursday, June 15, 2023