Long-lasting response in a subset of locally advanced rectal cancer patients in response to dostarlimab immunotherapy

June 2024

Early clinical results have shown that locally advanced (stage III) mismatch repair deficient (dMMR) rectal cancers can respond very well to immunotherapy alone, therefore allowing patients to avoid treatment with chemotherapy, radiation, or surgery. The long-term impact of immunotherapy treatment on this patient population, however, is unknown.

A phase II study investigated the efficacy of the immunotherapy agent dostarlimab in patients with locally advanced dMMR or microsatellite instability high (MSI-H) rectal cancer. 47 patients with dMMR locally advanced rectal cancer were enrolled to receive 6 months of dostarlimab, a PD-1 blocking immunotherapy agent.

PD-1 blocking therapies: these therapies target the immune system to re-wake the anti-tumour immune response.

The study

Among the 41 patients who completed treatment, all achieved a clinical complete response. This is defined as the disappearance of all signs of cancer in response to treatment. 20 patients, who were followed for a median of 28.9 months, achieved a sustained clinical complete response. A sustained clinical complete response is defined as no evidence of tumour by MRI, endoscopy, and digital rectal exam for at least 12 months following the end of treatment. Furthermore, no serious adverse events (any harmful or negative outcomes) greater than grade 2 on a scale of 4 as a result of treatment were observed.

Conclusion

Findings from this phase II study demonstrate that immunotherapy for 6 months alone produced long-lasting, recurrence-free responses in patients with locally advanced dMMR rectal cancer, thereby eliminating the need for chemotherapy, radiation, or surgery.