[18F] FDG PET/MR-defined EMVI predicts distant metastasis and reflects strong tumor invasiveness in rectal cancer

Introduction: Extramural vascular invasion in patients with rectal cancer is a poor prognostic factor associated with distant metastasis; thus, accurate preoperative diagnosis is important. However, the accurate detection of extramural vascular invasion using magnetic resonance imaging is difficult, and an improved diagnostic modality is required. In addition, the factors involved in the formation of EMVI remain unclear. In this study, we aimed to examine the ability of [18F] FDG PET/MRI to detect EMVI and 　elucidate the factors involved in EMVI.Methods: Thirty-one patients with rectal cancer were enrolled in this study between 2017 and 2021. We preoperatively evaluated the pelvic 18F-fluorodeoxyglucose positron emission tomography/ magnetic resonance imaging([18F] FDG PET/MRI) to detect extramural vascular invasion ([18F] FDG PET/MR-defined EMVI: pmrEMVI). To investigate the factors related to pmrEMVI, we confirmed the desmoplastic reaction and TWIST expression in the primary lesions of rectal cancer and examined its relationship with pmrEMVI.Results: Six of the 31 patients were pmrEMVI-positive. Four pmrEMVI-positive patients had distant metastases. The levels of immature desmoplastic reaction and TWIST1 expression were significantly higher in cases with pmrEMVI positivity.Conclusion: PmrEMVI is a useful biomarker for predicting distant metastasis. In addition, pmrEMVI was significantly correlated with factors related to tumor invasiveness.