Prognostic role of quantitative [18F]FDG PET/CT parameters in adrenocortical carcinoma

We aimed to evaluate the prognostic potential of baseline [¹⁸F]FDG PET/CT for overall survival (OS) in patients with adrenocortical carcinoma (ACC).

We performed a retrospective analysis of 67 treatment-naïve ACC patients with available [¹⁸F]FDG PET/CT at time of initial diagnosis. Pretherapeutic PETs of primary tumors were manually segmented and quantitative parameters (maximum/mean/peak standardized uptake value (SUV_{max/mean/peak}), metabolic tumor volume (MTV) and tumor lesion glycolysis (TLG, defined as TV*SUV_mean) were derived. Based on a visual read, absence (M0) or presence of metastatic disease (M1) were evaluated. Kaplan-Meier and Cox regression analyses were used to determine the prognostic value of the above mentioned markers on overall survival adjusted for established prognostic markers.

24/67 patients (36%) presented with M0 based on PET/CT, while the remaining 43/67 (64%) had M1-status. 32/67 patients died during follow-up and median OS was 48 months. In 12% of patients FDG-PET detected additional metastatic lesion not clearly visible by CT only. In univariable analysis, all quantitatively derived PET parameters failed to reach significance (P ≥ 0.1), and only PET/CT-based M1-status and Ki-67 were associated with increased mortality (M1: HR 13.89, 95% CI 4.15-86.32, P < 0.001; Ki-67 HR 1.29, 95% CI 1.16-1.42; P < 0.0001). Using multivariable Cox regression analyses, M1-status (HR 9.69, 95% CI 2.82-60.99) and Ki-67 index (HR 1.29, 95% CI 1.13-1.04; P < 0.05) remained significant associated with OS.

In treatment-naïve ACC patients, the quantitative PET parameter failed to predict OS, but presence of metastases detected by [¹⁸F]FDG PET/CT and Ki-67 index were independently associated with shorter OS. Therefore, a simple visual PET-based read-out is of prognostic value at initial diagnosis, while time-consuming PET-based quantification can be omitted.