[99mTc]Tc-FAPI-04 SPECT/CT for initial staging of gastrointestinal malignancies: a prospective comparison with contrast-enhanced CT

This single-center prospective pilot study evaluated [ 99m Tc]Tc-FAPI-04 SPECT/CT for initial staging in patients with newly diagnosed gastrointestinal (GI) malignancies and compared it directly with contrast-enhanced CT (ceCT) to assess its potential complementary staging value. Thirteen patients with suspected or histopathologically confirmed GI malignancies were prospectively enrolled between March and June 2025. All patients underwent both [ 99m Tc]Tc-FAPI-04 SPECT/CT and ceCT examinations. Using histopathology or composite clinical/imaging follow-up as the reference standard, the detection capabilities of both modalities for primary tumors, lymph node metastases, and distant metastases were compared, and the impact of FAPI imaging on clinical treatment decisions was recorded. Both modalities achieved 100% detection rates for primary tumors. For metastatic lesions, [ 99m Tc]Tc-FAPI-04 SPECT/CT showed higher sensitivity than ceCT at the lesion level (45.9% vs. 36.5%, P = 0.039). SPECT/CT detected 10 lesions missed by ceCT, predominantly in the peritoneum and mesentery (including regional lymph nodes), while ceCT identified 2 lesions missed by FAPI imaging (1 hepatic metastasis and 1 regional lymph node). In the pre-specified subgroup analysis of lymph node and tumor deposit metastases, FAPI SPECT/CT showed higher detection sensitivity than with ceCT (50.0% vs. 37.9%, P = 0.021). FAPI imaging identified occult peritoneal metastases missed by ceCT in one illustrative case, leading to upstaging and subsequent modification of the treatment strategy. Preliminary results indicate that [ 99m Tc]Tc-FAPI-04 SPECT/CT may provide complementary information for the initial staging of GI malignancies, particularly for occult peritoneal disease that may be difficult to detect on ceCT. Further studies with larger, tumor-specific cohorts are needed to validate its clinical utility.