Total neoadjuvant therapy involving checkpoint inhibitors in locally advanced MSI/dMMR rectal cancer - a case report.

Background: Typically, the management of locally advanced rectal cancer consists of neoadjuvant chemoradiotherapy, followed by surgery and adjuvant chemotherapy. In addition to neoadjuvant chemoradiotherapy, total neoadjuvant therapy (TNT) involving radiotherapy and combined chemotherapy has been increasingly used and shown to reduce the risk of distant metastasis and improve local control. Patients with microsatellite instability and deficient mismatch repair (MSI/dMMR) tumors represent a specific group that benefits from different approaches if TNT is considered.

Case: Our case report describes the diagnosis and treatment of a patient with locally advanced rectal cancer indicated for clinical characteristics to predictive molecular testing. Microsatellite instability was confirmed. Based on this finding, after short-course radiotherapy, she was offered neoadjuvant immunotherapy with checkpoint inhibitors. She subsequently underwent surgery with a confirmed pathologic complete response. The treatment was well-tolerated and she stays in complete remission, with a follow-up according to the standard recommendations.

Conclusion: This case highlights the importance of molecular testing in rectal cancer, which should be performed in all advanced cases requiring more intensive oncologic therapy than surgery alone. MSI/dMMR status indicates the need for a specific approach that may significantly improve the outcomes of these patients.