Feasibility study of 68 Gallium-FAPI PET-CT in staging of non-small cell lung carcinoma (NSCLC) and Invasive Ductal Carcinoma of Breast: Comparison with FDG PET-CT.

Introduction: Gallium 68 (⁶⁸Ga)–labelled fibroblast-activation protein inhibitor (FAPI) has recently been introduced as a promising tumour imaging agent. Initial reports suggested that gallium 68–labelled fibroblast-activation protein inhibitor PET/CT may outperform fluorine 18–labelled fluorodeoxyglucose PET/CT in staging lung and breast cancer, particularly in the detection of metastasis to the brain, lymph nodes, bone, and pleura.

Objectives:

• To establish the imaging protocol and evaluate feasibility of Gallium 68–labelled fibroblast-activation protein inhibitor PET/CT in newly diagnosed patients of carcinoma lung and carcinoma breast in our institution.

• To compare the role of Gallium 68 (⁶⁸Ga)–labelled fibroblast-activation protein inhibitor (FAPI) PET/CT with Fluorine 18–labelled fluorodeoxyglucose (FDG) PET/CT in staging of carcinoma lung and carcinoma breast.

Methods: The study was conducted in department of Nuclear Medicine of Tata Medical Centre, Kolkata in collaboration with department of Medical Oncology and Breast Oncology disease management group and department of Pathology. Sixteen patients, ten of primary lung malignancy and six of primary breast malignancy referred for FDG PET/CT for staging purpose was prospectively selected. Informed consent was taken from all the patients. The patients underwent 68-Ga FAPI PET/CT within 1 week of performing FDG PET/CT. Both the scans were visually evaluated for delineation of primary tumor and detection of suspected metastasis in lymph nodes & other visceral sites. Semi quantitative evaluation was performed by comparing SUVmax for reference lesions.

Results: Total 16 patients were recruited out of which 10 patients had primary lung malignancy and 6 patients had primary breast malignancy. Out of 16 patients 9 patients were female and 7 patients were male. Mean Age of the patients were 64.1 ± 11.1 years (Range 41-83 years). Concordant findings are noted in 8 out of 16 patients (50%) in both the imaging modalities. In rest of the patients, FAPI upstage the disease in 3 patients (18.75%), downstage the disease in 3 patients (18.75%). In remaining 2 patients (12.5%), FAPI show likely false negative uptake in mediastinal lymphnodes (1 patient) and adrenal glands (both patients). In lung carcinoma patients FAPI correctly changes the stage in 3 of 10 patients (30%) while it falsely downstage the disease in 2 of 10 patients (20%). In breast carcinoma patients it correctly changes the stage in 3 out of 6 patients (50%). SUVmax of primary breast malignancy is significantly higher for FAPI PET-CT when compared with FDG PET-CT (16.2 ± 3.9 vs 7.89 ± 4.1, p = 0.004). In most of the other lesions though FAPI PET-CT shows higher SUVmax value but it was not statistically significant due to small sample size.

Conclusions: Our initial experience suggests that FAPI PET-CT is feasible in primary staging of lung and breast carcinoma. It provides desirable performance with reasonably high accuracy in both the settings. When compared with FDG PET-CT it changes the stage of significant proportion of patients in both clinical scenarios which can further change the management. Metabolic parameter like SUVmax values are higher in most of the lesions in FAPI PET-CT when compared with FDG PET-CT which may be helpful for early detection of disease.