Added value of body MRI to detect primary abdominal malignancies in the diagnostic work-up of patients with adenocarcinoma of unknown primary

Purpose: This study aimed to evaluate the added benefit of body MRI (covering the chest, abdomen, and pelvis) to detect the primary tumour in patients with adenocarcinoma of unknown primary (ACUP) and a suspected abdominal malignancy in whom previous diagnostic work-up with CT and/or FDG-PET/CT did not yield a primary tumour diagnosis. Methods: Thirty ACUP patients with a suspected primary tumour in the abdomen/pelvis (based on pathology and/or pattern of disease) underwent MRI (T2-weighted, DWI, pre- and post-contrast T1-weighted) after completion of their initial diagnostic work-up with CT and/or PET/CT. Effects of MRI to establish a primary tumour diagnosis (and to detect additional metastatic sites) were documented. Integration of all available imaging data, additional diagnostic procedures (e.g., endoscopy), histopathology, and whole genome sequencing served as the composite standard of reference. Results: MRI rendered a possible primary tumour diagnosis in 16/30 (53%) cases, which aligned with the final clinical diagnosis in 9/16 (56%) of these cases, thus resulting in a confirmed primary tumour diagnosis in 30% of our total patient cohort. These included four gastrointestinal, two hepatobiliary, one pancreatic, one ovarian and one breast cancer. MRI revealed extra metastatic sites in five patients (17%). Conclusion: MRI can be of added value in the diagnostic work-up of ACUP patients with a suspected primary tumour originating from the abdomen or pelvis, in particular to detect gastrointestinal or hepatobiliary malignancies. Larger studies are needed to confirm these results and identify specific ACUP patients that are most likely to benefit from MRI. Key Points: Question Can body MRI help identify the primary tumour in patients with adenocarcinoma of unknown primary (ACUP)? Findings In this pilot of n = 30 ACUP patients with clinically suspected abdominal malignancies, body MRI was able to establish the primary tumour in 30% of cases. Clinical relevance Body MRI can be of added value (as an adjunct to CT and/or PET/CT) in the diagnostic work-up of ACUP patients with a suspected primary tumour originating from the abdomen or pelvis, especially to detect gastrointestinal or hepatobiliary malignancies.