Clinicopathological, Oncogenic, and 18F-FDG PET/CT Features of Primary Pulmonary Carcinoid in Resection Specimens

Abstract

Objectives. The metabolic parameters which included mean standardised uptake value (SUVmean), metabolic tumour volume (MTV), total lesion glycolysis (TLG), maximum standardised uptake lean body mass (SULmax), and maximum standardised uptake body surface area (SUVbsa) have rarely been investigated in pulmonary carcinoid (PC). This study aimed to retrospectively compare the 18F-FDG PET/CT features of PC subtypes and observe clinicopathological and oncogenic characteristics of PC. Methods. We performed a retrospective review in 60 patients with PC, from January 2016 to November 2021, who underwent the 18F-FDG PET/CT scan. All the PC diagnoses were histopathologic confirmed by surgical samples. The metabolic and morphological features were obtained from 18F-FDG PET/CT images. The ratio of metabolic to morphological lesion volumes (MMVR) was calculated. Results. Sixty patients with PC were consecutively identified, including 39 patients (65.0%) with typical carcinoids (TCs) and 21 (35.0%) with atypical carcinoids (ACs). One (1/21) patient had mutation in BRAF. The ACs have a larger size ( $P$  < 0.001), more metastatic lymph nodes ( $P$  = 0.011), higher Ki-67 expression ( $P$  < 0.001), higher SUVmax values ( $P$  = 0.003), higher SUVmean values ( $P$  = 0.006), higher SULmax values ( $P$  = 0.005), higher SUVbsa values ( $P$  = 0.001), higher MTV values ( $P$  = 0.033), and higher TLG values ( $P$  = 0.002). The multivariate analysis showed that MMVR ( $P$  = 0.020) was significantly associated with AC. For predicting AC, the optimal cut-off value of SUVmax, SUVmean, SULmax, SUVbsa, MTV, TLG, and the maximum diameter was 5.19, 3.18, 2.65, 1.47, 4.36, 18.44, and 3.0, respectively. The AUC values of above mentioned parameters was 0.756 (95%CI, 0.631–881; $P$  = 0.001), 0.735 (95%CI, 0.602–868; $P$  = 0.003), 0.736 (95%CI, 0.607–865; $P$  = 0.003), 0.742 (95%CI, 0.612–873; $P$  = 0.002), 0.593 (95%CI, 0.430–755; $P$  = 0.239), 0.680 (95%CI, 0.531–829; $P$  = 0.022), and 0.733 (95%CI, 0.598–868; $P$  = 0.003), respectively. For predicting TC, the optimal cut-off value of the MMVR was 0.92, and the AUC value was 0.780 (95%CI, 0.647–0.913; $P$  < 0.001). Conclusion. 18F-FDG PET/CT can simultaneously reveal the metabolic and morphological characteristics of PC, which is important in the differentiation for histopathologic subtypes.