Predictive value of dual-time ¹⁸F-FDG PET/CT to distinguish primary lung and metastatic adenocarcinoma in solitary pulmonary nodule

Aims and background:Distinction between primary lung adenocarcinoma and metastatic adenocarcinoma from extrapulmonary origin in solitary pulmonary nodule (SPN) is crucial for cancer treatment. We investigated the predictive role of dual-time-point ¹⁸F-FDG PET/CT to distinguish primary and metastatic lung adenocarcinoma in SPN. Methods: A total of 96 consecutive patients with newly diagnosed SPN and biopsy-proven adenocarcinoma were enrolled in this study, retrospectively (54 male; 42 female; age 59.68 ± 8.2 years). They all underwent dual-time-point ¹⁸F-FDG PET/CT at 60 minutes (early) for whole body and 120 minutes (delayed) for chest region after FDG injection. Maximum standardized uptake values (early SUVmax and delayed SUVmax) and retention index (RI) were acquired for analysis. Final pathology results were confirmed by surgical specimens. Results: Metastatic adenocarcinoma showed significantly higher early SUVmax, delayed SUVmax, and RI compared to primary lung adenocarcinoma. Delayed SUVmax and RI presented superior diagnostic performance for prediction of metastatic adenocarcinoma than early ¹⁸F-FDG PET/CT. Among metastatic adenocarcinoma, metastasis from colorectal origin showed significantly higher RI than from other origins. In addition, RI significantly predicted metastatic adenocarcinoma from colorectal cancer than early or delayed SUVmax. Conclusions: Dual-timepoint ¹⁸F-FDG PET/CT can be useful to distinguish primary and metastatic lung adenocarcinoma in SPN. Furthermore, it may also be useful to predict metastatic adenocarcinoma from colorectal origin.