Study of 18FET PET in Functional Pituitary Adenomas With Indeterminate MRI Findings

18F-fluoro-ethyl-tyrosine (18FET) PET for Difficult Clinical Situations in Functional Pituitary Adenoma. A Prospective, Single Arm, Single Center Study

Pituitary adenomas (PAs) are common benign tumors, but their potential for tumor aggression and hormone secretion make them serious tumors. In particular, patients with secreting tumors [prolactinomas (prolactin secretion), acromegaly (growth hormone), Cushing's disease (ACTH), thyrotropic adenomas (TSH)] have increased morbidity and mortality. They may be small and/or undetectable by magnetic resonance imaging (MRI), the current gold standard for morphological evaluation of pituitary lesions. The diagnosis of recurrence in a patient who has already undergone surgery also raises the problem of distinguishing between a lesion and postoperative remodeling. The detection of these tumors therefore represents a significant challenge in guiding therapeutic management.Nuclear medicine could solve this challenge, particularly radiopharmaceuticals (MRPs) used in PET (positron emission tomography) combined with CT scans. A few studies have evaluated MRPs in the context of APs, with those targeting amino acid metabolism proving to be the most promising, particularly carbon-11-labeled methionine (11C-MET). In retrospective studies only, 11C-MET PET has shown excellent performance in all situations where MRI fails (detection rate >80%), but the extremely short half-life of 11C requires heavy infrastructure, limiting its access in routine clinical practice.18Fluoroethyl-Tyrosine (18FET) is also a PET MRP targeting amino acid metabolism used in France in neuro-oncology with performance equivalent to 11C-MET, and which has the advantage of being available daily in all nuclear medicine centers.

The performance of 18FET in APs is almost unknown, with only two retrospective studies recently published, including 22 patients with Cushing's disease on the one hand and 17 patients with prolactinoma on the other: The detection rates were particularly interesting (82% and 100% respectively), but it is imperative to confirm these data prospectively and to evaluate the performance of this MRP in other functional types, which is therefore the purpose of this study.

Inclusion Criteria:

• Male and/or female
• Aged 18 years or older
• Suspected of having a functional pituitary adenoma (prolactinoma - Cushing's disease - acromegaly - thyrotropic adenoma), de novo or recurrence/persistence
• With indeterminate pituitary MRI
• Patient covered by social security
• Patient willing to comply with all study procedures and duration
• Patient eligible for surgery and/or radiotherapy in case of positive 18FET PET scan

Exclusion Criteria:

• Pregnancy
• Known hypersensitivity to radiopharmaceuticals
• Administrative reasons: inability to receive informed information, inability to participate in the entire study, lack of coverage by the social security system, refusal to sign the consent form
• Contraindication to surgery and radiotherapy in the case of positive 18FET PET
• Patients who are active alcohol users
• Patients suffering from liver disease or severe uncontrolled epilepsy
• Patients deprived of their liberty (guardianship, curatorship, etc.)