Prospective Trial of [18F]AlF-FAPI-74 for PET Imaging of Fibroblast Activation Protein in Patients With Endometriosis

Inclusion Criteria:

* Voluntary written informed consent of the participant has been obtained prior to any screening procedures.
* At least 18 years of age at the time of signing the Informed Consent Form (ICF).
* At least one of the following to be eligible for the DE cohort: (i) Clinical suspicion of DE, defined as the presence of deep nodule(s) during vaginal examination determined by a clinician who is an expert in endometriosis. (ii) Diagnostic suspicion of DE, defined as an ultrasound and/or MRI that shows lesions suspicious for DE.
* At least one of the following to be eligible for the SPE cohort: (i) Clinical suspicion of SPE, defined as clinical symptoms suspicious of SPE determined by a clinician who is an expert in endometriosis. These clinical symptoms include dysmenorrhea, deep dyspareunia, dysuria, dyschezia, painful rectal bleeding or haematuria, shoulder tip pain, catamenial pneumothorax, cyclical cough/haemoptysis/chest pain, cyclical scar swelling and pain, fatigue, and infertility. (ii) Diagnostic suspicion of SPE, defined as an ultrasound and/or MRI that shows lesions suspicious for SPE.
* Planned laparoscopy for suspected endometriosis.

Exclusion Criteria:

* For SPE cohort: (i) Ultrasound and/or MRI with lesions suspicious of ovarian endometriosis and/or DE. (ii) Clinical symptoms suspicious of ovarian endometriosis and/or DE, determined by a clinician who is an expert in endometriosis.
* Prior abdominal surgery less than one year ago.
* Female who is pregnant, breastfeeding or is of childbearing potential and not using an adequate, highly effective contraceptive or no usage of contraception when sexually active are not accepted.
* Participant is mentally or legally incapacitated, does not understand the study design or is not willing or capable to undergo all study-specific procedures.
* Any disorder or condition, which in the Investigator's opinion might jeopardise the participant's safety or compliance with the protocol, or may influence the result of the study.
* Any prior or concomitant treatment(s) that might jeopardise the participant's safety or that would compromise the integrity of the Trial.
* Participation in an interventional Trial with an investigational medicinal product (IMP) or device when the trial designs are not considered compatible by the study team.
* Participation in a clinical scientific study in the last 12 months with a radiation exposure caused by the experimental procedures greater than 1 mSv.
* Participant has a known hypersensitivity to \[18F\]AlF-FAPI-74 or the used excipients.

A \[18F\]AlF-FAPI-74 PET/CT will be performed at UZ Leuven before the participant's planned laparoscopy. Participants are required to fast for 4 hours before tracer administration but water is allowed. An intravenous line will be placed and \[18F\]AlF-FAPI-74 will be administered in one bolus (3.5 MBq/kg). PET/CT acquisition will start after 60 minutes. The CT will be a low dose CT with oral contrast. If there are no contraindications, 20 mg Buscopan may be administered shortly before imaging to reduce bowel movement.

Participants may optionally undergo an additional NeuroEXPLORER PET/CT scan on the same day after the same \[18F\]AlF-FAPI-74 administration, so no second tracer injection is required. Participants who start treatment with a GnRH (ant)agonist after their first scan may undergo a second \[18F\]AlF-FAPI-74 PET/CT to investigate changes in tracer uptake during hormonal treatment. Participants will be monitored for adverse events related to study procedures.

A \[18F\]AlF-FAPI-74 PET/CT will be performed at UZ Leuven before the participant's planned laparoscopy. Participants are required to fast for 4 hours before tracer administration but water is allowed. An intravenous line will be placed and \[18F\]AlF-FAPI-74 will be administered in one bolus (3.5 MBq/kg). PET/CT acquisition will start after 60 minutes. The CT will be a low dose CT with oral contrast. If there are no contraindications, 20 mg Buscopan may be administered shortly before imaging to reduce bowel movement.

Participants may optionally undergo an additional NeuroEXPLORER PET/CT scan on the same day after the same \[18F\]AlF-FAPI-74 administration, so no second tracer injection is required. Participants will be monitored for adverse events related to study procedures.

Not reported.

Not reported.