¹⁸F-FAMT in patients with multiple myeloma: clinical utility compared to ¹⁸F-FDG.

Objective: L-[3-(18)F]-alpha-methyltyrosine ((18)F-FAMT) is an amino-acid tracer for positron emission tomography (PET), with uptake related to overexpression of L-type amino-acid transporter 1 and proliferative activity in tumour cells. This study evaluated the diagnostic performance of (18)F-FAMT PET compared with 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG) PET in patients with multiple myeloma (MM).

Methods: Eleven patients with MM (newly diagnosed, n = 3; relapsed after treatment, n = 8) underwent whole-body (18)F-FAMT and (18)F-FDG PET within a 2-week interval. Magnetic resonance imaging (MRI) of the spine was also performed to assess patterns of bone marrow infiltration. Tracer uptake was semi-quantitatively evaluated using maximal standardized uptake value (SUV(max)). Mean SUV was also determined for normal bone marrow and the aortic arch as mediastinal background SUV to calculate lesion-to-bone marrow (L/B) and lesion-to-mediastinum (L/M) ratios, respectively. Those values were statistically compared using Student's t test.

Results: In 8 patients showing focal infiltration on MRI, 34 FDG-avid bone lesions were identified, with each showing increased FAMT uptake. Mean SUV(max) and L/B ratio of FDG (3.1 ± 1.2 and 3.3 ± 1.9, respectively) were significantly higher than those of FAMT (2.0 ± 1.0 and 2.6 ± 1.1, respectively; p < 0.05 each). In contrast, the L/M ratio of FDG showed no significant difference to that of FAMT (2.2 ± 1.0 and 2.4 ± 1.2, respectively; p = 0.3).

Conclusions: Clear (18)F-FAMT PET uptake was seen in most (18)F-FDG-avid lesions among patients with MM, and an equivalent semi-quantitative value was obtained using L/M ratio. Our preliminary data suggest that (18)F-FAMT PET provides a useful imaging modality for detecting active myelomatous lesions.