The goal of this observational pilot study is to explore whether we can identify biomarkers predictive for the diagnosis of adrenocortical carcinoma in blood. Five participants who are suspected to have adrenocortical carcinoma will undergo an adrenal vein sampling in order to obtain a blood sample from the adrenal vein. This blood sample will be analyzed and compared to blood samples taken from the adrenal vein of 20 control patients, which are patients who do not have adrenocortical carcinoma. The blood samples of the control patients will be drawn during routine medical care.

Inclusion Criteria:

In order to be eligible to participate in the study group, a subject must meet all of the following criteria:

• Patient age ≥18 years
• High clinical suspicion of adrenocortical carcinoma, based on clinical signs (due to hormonal overproduction), steroid hormone profile and radiological features (e.g. tumor size ≥4cm, inhomogenous aspect and tumor attenuation of HU ≥10)
• Able to provide signed informed consent

In order to be eligible to participate in the control group, a subject must meet all of the following criteria:

• Patient age ≥18 years
• Routine diagnostic process includes AVS
• No suspicion of malignancy
• Able to provide signed informed consent

Exclusion Criteria:

Patients are not able to participate if:

• They have a known allergy to (iodinated) contrast fluid
• They use vitamin K antagonizing anticoagulants or DOAC's, except for when on the day of the adrenal vein sampling the anticoagulants are already stopped for the following adrenal surgery, and in case of using vitamin K antagonizing anticoagulants the INR is <3
• The platelet count is below 20
• Anatomy of the adrenal vein is not suitable for performing the AVS procedure, based on the judgement of an experienced interventional radiologist
• Contraindications for use of Synacthen
• They have a known hypersensitivity to any of the substances of Synacthen
• They are pregnant

The study population consists of patients with a strong clinical suspicion of adrenocortical carcinoma. The control population consists of patients without suspicion of malignancy. The most important for the participants in the control group is that their routine diagnostic tests should include an adrenal vein sampling.