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Evaluating MRI response criteria in microsatellite instability-high rectal cancer treated with immune checkpoint
Q Vanderbecq1, R Cohen2, M Camus3
1Department of Radiology, AP-HP, Sorbonne, Saint-Antoine Hospital, Paris, France; UMR 7371, Université Sorbonne, CNRS, Inserm U114615, Paris, France.
Background:
Immune checkpoint inhibitors (ICIs), particularly anti-programmed cell death protein 1 (PD-1) agents, have enabled consideration of non-operative management in patients with microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) rectal cancer. Standard magnetic resonance imaging (MRI) response criteria-developed for chemoradiotherapy-may not accurately reflect treatment effects with ICIs, however.
Patients And Methods:
We retrospectively analyzed 14 patients with locally advanced MSI-H/dMMR rectal adenocarcinoma treated with neoadjuvant anti-PD-1 monotherapy. All patients achieved a complete pathological response. MRI assessment included T2-weighted, diffusion-weighted, and contrast-enhanced sequences. Treatment response was defined as complete pathological response by surgical pathology (proctectomy), or by endoscopic and biopsy-confirmed complete remission (watch-and-wait strategy).
Results:
MRI showed distinct post-treatment patterns: split scar sign (n = 2), fibrotic response (n = 5), lesion disappearance (n = 1), and residual intermediate T2 signal (n = 6). All mucinous tumors retained T2-hyperintense residues. In select cases, fibrotic response was beyond 3 months. In two surgical cases, histological analysis revealed residual mucinous material without viable tumor cells.
Conclusions:
MRI response patterns after anti-PD-1 monotherapy in MSI-H/dMMR rectal cancer differ from those observed after radiochemotherapy, suggesting the need to adapt current imaging criteria for accurate response assessment and informed surgical decision making. Persistent MRI abnormalities are frequent despite complete pathological response, and warrant cautious interpretation in the ICI setting.
Insights
Magnetic resonance imaging (MRI) shows unique patterns after anti-programmed cell death protein 1 (PD-1) therapy for rectal cancer. These findings differ from standard criteria, requiring updated imaging assessments for patients with microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) rectal cancer.
Area of Science:
- Oncology
- Radiology
- Immunotherapy
Background:
- Immune checkpoint inhibitors (ICIs), specifically anti-PD-1 agents, are used for microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) rectal cancer.
- Standard MRI criteria for response assessment were developed for chemoradiotherapy and may not apply to ICI treatment.
- Accurate response evaluation is crucial for non-operative management and surgical decisions.
Purpose of the Study:
- To investigate MRI-based response patterns in patients with MSI-H/dMMR rectal cancer treated with neoadjuvant anti-PD-1 monotherapy.
- To compare these patterns with those typically seen after conventional chemoradiotherapy.
- To highlight the need for adapted MRI criteria in the context of ICI therapy.
Main Methods:
- Retrospective analysis of 14 patients with locally advanced MSI-H/dMMR rectal adenocarcinoma.
- Treatment involved neoadjuvant anti-PD-1 monotherapy.
- MRI included T2-weighted, diffusion-weighted, and contrast-enhanced sequences.
- Pathological complete response was confirmed via surgery or endoscopic/biopsy-confirmed complete remission.
Main Results:
- All 14 patients achieved a pathological complete response.
- Observed MRI patterns included split scar sign (2), fibrotic response (5), lesion disappearance (1), and residual intermediate T2 signal (6).
- Mucinous tumors consistently showed T2-hyperintense residues, and fibrotic responses sometimes persisted beyond 3 months.
- Histological analysis in surgical cases revealed residual mucin without viable tumor cells.
Conclusions:
- MRI response patterns following anti-PD-1 monotherapy for MSI-H/dMMR rectal cancer are distinct from those after chemoradiotherapy.
- Current imaging criteria may require adaptation for accurate response assessment in the ICI setting.
- Persistent MRI abnormalities are common despite complete pathological response, necessitating careful interpretation for surgical decision-making.
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