Diagnostic value of [⁶⁸Ga]Ga-Pentixafor PET/CT in malignant melanoma: a pilot study

Objective To evaluate the diagnostic value of [Ga-68] Ga-Pentixafor in malignant melanoma patients. Methods In this prospective study, patients with histology-proven melanoma were included and underwent [F-18]fluoro-D-glucose ([F-18]FDG) and [Ga-68] Ga-Pentixafor PET/computed tomography (CT) within a week. Suspicious lesions were interpreted as benign vs. malignant, and the corresponding semi-quantitative PET/CT parameters were recorded and compared. Results Twelve consecutive melanoma patients (mean age: 60 +/- 6) were included. Two patients were referred for initial staging, two for detecting recurrence and eight for evaluating the extent of metastases. Overall, [F-18]FDG PET/CT showed 236 tumoral lesions, including two primary tumors, two recurrent lesions, 29 locoregional metastases and 203 distant metastases. In [Ga-68]Ga-Pentixafor PET/CT, 101 tumoral lesions were detected, including two primary tumors, one recurrence, 16 locoregional metastases and 82 distant metastases. Notably, a documented brain metastasis was only visualized on [Ga-68]Ga-Pentixafor PET/CT images. Compared with [F-18]FDG, [Ga-68]Ga-Pentixafor PET/CT provided a 42% detection rate. Regarding semi-quantitative measures, the intensity of uptake and tumor-to-background ratios were significantly lower on [Ga-68]Ga-Pentixafor PET/CT [average maximum standard uptake value (SUVmax) of 2.72 +/- 1.33 vs. 11.41 +/- 14.79; P value <0.001 and 1.17 +/- 0.53 vs. 5.32 +/- 7.34; P value <0.001, respectively]. Conclusion When comparing [Ga-68]Ga-Pentixafor PET/CT with [F-18]FDG PET/CT, not only did [Ga-68]Ga-Pentixafor PET/CT detect fewer lesions, but the intensity of uptake and the TBRs were also lower on [Ga-68]Ga-Pentixafor PET/CT. Thus, our results may indicate a limited potential of this novel tracer in cutaneous melanoma patients compared to [F-18]FDG PET/CT. Given the lower TBRs, applying this radiotracer in radioligand therapies is also questionable.