Signet cell rectal carcinoma with prostatic involvement detected by FAPI-04 PET-MRI fusion

Area of Science:

• Oncology
• Nuclear Medicine
• Radiology

Background:

• Mucinous adenocarcinoma of the rectum requires precise monitoring for recurrence.
• Standard imaging like F-18 FDG PET-CT may not always detect subtle or localized recurrences.
• Fibroblast activation protein (FAPI) is a promising target for imaging cancer-associated fibroblasts.

Purpose of the Study:

• To evaluate the utility of Gallium-68 FAPI-04 (Ga-68 FAPI-04) PET-CT in detecting recurrent rectal cancer.
• To compare the diagnostic performance of Ga-68 FAPI-04 PET-CT with F-18 FDG PET-CT in a patient with suspected recurrence.

Main Methods:

• A patient with treated rectal cancer and rising CEA levels underwent restaging with F-18 FDG PET-CT.
• Subsequent evaluation with Ga-68 FAPI-04 PET-CT was performed due to persistent suspicion.
• Pelvic MRI was utilized and fused with Ga-68 FAPI-04 PET-CT for confirmation.

Main Results:

• Initial F-18 FDG PET-CT showed no obvious malignant disease despite rising CEA levels.
• Ga-68 FAPI-04 PET-CT revealed disease involvement in the prostate and seminal vesicles.
• Fused imaging confirmed prostatic involvement, identifying recurrence missed by standard PET-CT.

Conclusions:

• Ga-68 FAPI-04 PET-CT demonstrates superior sensitivity for detecting localized recurrence of rectal cancer compared to F-18 FDG PET-CT.
• FAPI-targeted imaging offers a valuable tool for restaging and managing patients with suspected recurrent gastrointestinal malignancies.
• This case highlights the potential of FAPI PET-CT in identifying disease sites not visualized by conventional PET tracers.