Open Access

Jörg Trojan, Sebastian Jörg Stintzing, Oliver Haase, Christine Koch, Paul Ziegler, Melanie Christin Demes, Ivan Jelas

• Background: Patients with colorectal carcinoma and high-grade microsatellite instability (MSI-H) or deficiency in mismatch repair (dMMR) exceptionally respond to immune checkpoint inhibitors (ICIs). ICIs are more active in treatment-naïve patients than in patients with refractory MSI-H/dMMR metastatic colorectal cancer and even more active in patients with locally advanced tumors. Material and Methods: A 33-year-old male patient with Lynch syndrome was diagnosed with a locally advanced rectal cancer and refused standard neoadjuvant chemoradiation because of the potential harm of sexual dysfunction. MMR and microsatellite instability status were analyzed by immunohistochemistry and fragment length polymerase chain reaction followed by capillary electrophoresis. Results: After MSI-H/dMMR was confirmed, the patient was treated with ICIs (1 mg/kg ipilimumab at day 1 and 3 mg/kg nivolumab at day 1 and 15). A complete clinical response was documented at day 21 after start of treatment. The patient underwent a total mesorectal excision at day 30. In the extirpated tissue, a complete pathological response was confirmed. Conclusion: In MSI-H/dMMR locally advanced rectal cancer short-course ICI treatment is highly effective and may be discussed in patients with dMMR locally advanced rectal cancer.