The aim of the suggested study is to assess the added value of 68Ga-FAPI-04 PET/CT over 18F-FDG PET/CT in evaluating the extent of disease in patients with various malignancies, in whom a diagnostic challenge is met, such as inconclusive findings on 18F-FDG PET/CT or other imaging studies, better delineation of tumor extent prior to therapy, and with emphasis on malignancies known to show variable avidity to FDG and at times, no uptake at all. Also patients unable to optimally comply with the required preparation for FDG imaging, such as diabetic patients who struggle in achieving glycemic control.

Inclusion Criteria:

The study population will include up to 50 patients with disease in whom a diagnostic challenge is met, including but not limited to:

1. Inconclusive findings on 18F-FDG PET/CT or other imaging modalities.

2. Better delineation of tumor extent prior to therapy

3. Malignancies known to show variable avidity to FDG and at times, no uptake at all (e.g. Exocrine Pancreatic cancer, Gastric carcinoma, Mucin-producing or Signet-ring carcinoma).

4. Patients unable to optimally comply with the required preparation for FDG imaging.

   • The study population will include only patients treated in Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel, and referred by their attending physicians, of whom are part of the hospital staff.

Exclusion Criteria:

• Age < 18 years.
• Pregnant females.
• Patients who are reluctant to undergo both FDG and FAPI PET scans.