Head-to-head comparison of (68 Ga) Ga-FAPI and 18F-FDG PET/CT in evaluating hepatobiliary and pancreatic malignancies – Prospective study

Introduction: To compare the diagnostic accuracy of ¹⁸F-FDG PET/CT and ⁶⁸Ga-PET CT PET/CT for the staging of Hepatobiliary and pancreatic malignancies.

Methods: This is a single centre prospective study performed between March 2022 to December 2022. We recruited 34 patients who were either suspected or diagnosed cases of HPB malignancies. Histopathological examination, morphological imaging and / or follow up imaging were taken as standard.

Results: 34 patients (mean age, 56 ± 10 SD; 23 male and 11 female) were analysed. 17 patients with intra and extra hepatic cholangiocarcinoma, 10 patients with pancreatic malignancy, 4 patients with hepatocellular carcinoma (HCC) and 3 patients with gall bladder (GB) carcinoma.

(⁶⁸ Ga) Ga-FAPI PET CT showed higher SUVmax and higher sensitivity in detection / evaluation of primary tumours (SUVmax 12.8 Vs 4.5 in cholangiocarcinoma; SUVmax 18 Vs 5 in gall bladder cancer; 20.6 Vs 5.4 in HCC; SUVmax 16.1 Vs 5.7 in pancreatic malignancies) (table).

In cholangiocarcinoma, 7 patients had lymph nodal metastases, (⁶⁸ Ga) Ga-FAPI PET CT study detected metastases in 2 patients which were missed in FDG study, distant metastases were seen in 4 patients which were detected in both scans. In GB cancer, 2 patients had lymph nodal and distant metastases, which were detected in both scans. In HCC, only one patient had regional lymph nodal metastases, detected in both scans. In pancreatic cancer, 7 patients had lymph nodal and distant metastases, FDG scan missed distant metastasis in one patient. However, diffuse pancreatitis is major drawback in patinets wtih pancreatic carcinoma, which may mask primary lesion. Overall, FAPI upstaged in 3 patients (3/21 patients).

Primary tumour

FDG

FAPI

BIOPSY

Cholangiocarcinoma

True negative: 2

True negative: 2

Negative = 3

False positive: 1

False positive: 1

Specificity: 66.6%

Specificity: 66.6%

True positive: 9

True positive: 14

Positive = 14

False negative: 5

False negative: 0

Sensitivity: 64%

Sensitivity: 100%

Gall bladder

True positive: 2

True positive: 3

Positive = 3

False negative: 1

False negative: 0

Sensitivity: 66.6%

Sensitivity: 100%

Hepatocellular carcinoma

True positive: 4

True positive: 4

Positive = 4

False negative: 0

False negative: 0

Sensitivity: 100%

Sensitivity: 100%

Pancreatic malignancy

True negative: 1

True negative: 1

Negative=1

False positive: 0

False positive: 0

Specificity: 100%

Specificity: 100%

True positive: 9

True positive: 9

Positive = 9

False negative: 9

False negative: 0

Sensitivity: 100%

Sensitivity: 100%

Conclusions: In our study, (⁶⁸ Ga) Ga-FAPI PET CT shows higher sensitivity in detection of primary tumours in HPB malignancies, upstaging in 14% of patients. However, prospective trials with larger patient population are needed to confirm whether [⁶⁸Ga] Ga-FAPI PET/CT could be utilised for treatment modification when compared with standard of care imaging. Also, diffuse intense FAPI uptake in pancreas may preclude detection of primary lesion.

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