Performance of [18F]-FDG PET/CT-derived Semi-Quantitative Parameters in Primary Tumor Staging of Mycosis Fungoides

Introduction: Mycosis fungoides (MF) is the commonest primary cutaneous T-cell lymphoma and is characterized by clonal proliferation of T-lymphocytes with cerebriform nuclei originating in the epidermis. Diagnosis and staging of MF is reliant on clinical and histopathological features. The role of Flourine-18 Flourodeoxyglucose ([¹⁸F]-FDG) PET/CT is not well established in staging MF. The aim of this study was to retrospectively analyze primary disease detection rate of [¹⁸F]-FDG PET/CT based on tumor stage at initial staging.

Methods: Seventeen patients with proven histology of mycosis fungoides were enrolled in the present study. [¹⁸F]-FDG PET/CT Whole body qualitative assessment of skin lesions with uptake greater than mediastinal background correlating to clinically visualized skin lesions was reported as positive. Maximum standardized uptake value (SUVmax) and SUVmean of the most intense skin lesions at baseline [¹⁸F] FDG-PET were measured.

Results: The median age was 54 years (32-74 years). The cohort included 5 patients patches (Tumor stage 1 - T1), 8 patients with plaques (T2), 3 patients with tumors (T3) and 1 patient with erythroderma (T4). Only 1 patient with patches had positive skin lesions on PET/CT with SUVmax and SUVmean of 2.4 and 2.01 respectively. Five of 8 patients with plaques (62.5%) and all 3 patients with tumors (100%) had [¹⁸F]-FDG PET/CT positivity. The only patient with erythroderma (T4) had no skin [¹⁸F]-FDG avidity. SUVmax and SUVmean values of skin lesions correlated with stage of disease. Mean SUVmax and SUVmean in plaques were 4.16(2.94-7.29) and 2.77(2.45-3.38) respectively. Mean SUVmax and SUVmean for tumors were 9.57(2.86-17.77) and 4.13(2.59-5.93) respectively.

Conclusions: The metabolic activity of skin lesions correlate with increasing tumor stage with higher SUVmax and SUVmean correlating to T3 (tumor) disease. [¹⁸F]-FDG PET/CT can be an objective imaging index for diagnosis and staging of MF.