Clinical impact of PET/MRI in oligometastatic colorectal cancer

Abstract

Background: Oligometastatic colorectal cancer (CRC) is potentially curable and demands individualised strategies.

Methods: This single-centre retrospective study investigated if positron emission tomography (PET)/magnetic resonance imaging (MR) had a clinical impact on oligometastatic CRC relative to the standard of care imaging (SCI). Adult patients with oligometastatic CRC on SCI who also underwent PET/MR between 3/2016 and 3/2019 were included. The exclusion criterion was lack of confirmatory standard of reference, either surgical pathology, intraoperative gross confirmation or imaging follow-up. SCI consisted of contrast-enhanced (CE) computed tomography (CT) of the chest/abdomen/pelvis, abdominal/pelvic CE-MR, and/or CE whole-body PET/CT with diagnostic quality (i.e. standard radiation dose) CT. Follow-up was evaluated until 3/2020.

Results: Thirty-one patients constituted the cohort, 16 (52%) male, median patient age was 53 years (interquartile range: 49-65 years). PET/MR and SCI results were divergent in 19% (95% CI 9-37%) of the cases, with PET/MR leading to management changes in all of them. The diagnostic accuracy of PET/MR was 90 ± 5%, versus 71 ± 8% for SCI. In a pairwise analysis, PET/MR outperformed SCI when compared to the reference standard (p = 0.0412).

Conclusions: These findings suggest the potential usefulness of PET/MR in the management of oligometastatic CRC.

Conflict of interest statement

The authors declare no competing interests.

© 2021. The Author(s), under exclusive licence to Springer Nature Limited.

Figures

Fig. 1. Peritoneal disease detected at PET/MR only.

Axial CE-CT (a), PET/MR axial T2-weighted high resolution (b), and fused PET/MR (c), from a 55-year-old female patient with oligometastatic rectal cancer, who had already undergone rectal surgery. The axial CT shows a presacral soft-tissue nodule, inseparable from the anastomosis, suspicious for tumour recurrence (arrow in a). On the PET/MR, the same lesion did not demonstrate increased FDG uptake (short arrow in b, c). There is, however, unexpected peritoneal disease involving the serosa of the sigmoid colon that was not seen on CT (long arrow in b, c). Both scans were performed 19 days apart. Due to the demonstration of peritoneal metastases by PET/MR, the patient was placed on chemotherapy instead of the original surgical approach which included liver metastasectomy and pelvic recurrence resection. The findings were confirmed by follow-up CE-MR performed 73 days later.

Fig. 2. Viable metastasis diagnosed by PET/MR.

Axial fused PET/CT (a), axial fused PET/MR (b), PET/MR contrast-enhanced VIBE (c), low b-value diffusion-weighted imaging (DWI) (d), and apparent diffusion coefficient (ADC) map (e). 50-year-old female patient with oligometastatic rectal cancer. PET/CT did not show residual hepatic metastases. However, a residual metastasis in segment VI/VII (arrow) was diagnosed by PET/MR. The lesion is harder to call a metastasis on PET/CT. Compared to PET/CT, the longer PET acquisition time along with the combined information from restricted diffusion and enhancement pattern on PET/MR allowed lesion detection and characterisation. Therefore, the patient underwent a liver metastasectomy in addition to the already planned chemoradiation therapy. Both scans were performed on the same day, and the pathology report from the liver metastasectomy specimen confirmed the PET/MR finding.