Bowel cancer is the third most common cancer in Australia.
Around 69% of bowel cancers are located in the colon and 31% in the rectum.
Each year there are 4,919 new rectal cancer cases and 2,815 rectal cancer deaths.
Around 5-10% of rectal cancers are microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR). These cancers are relatively resistant to chemotherapy, which forms part of the current standard of care for stage II and III rectal cancer – chemotherapy, radiation and surgery.
In a new phase 2 trial in the United States looking at patients with dMMR stage II or III rectal cancer, a single agent immunotherapy, dostarlimab, was administered via infusion every 3 weeks for 6 months with a view to following up with chemotherapy, radiation and surgery. A total of 12 patients completed treatment with dostarlimab, with follow-up ranging from 6 to 25 months.
All 12 patients had a clinical complete response, with no progression, recurrence or serious side effects reported in the follow-up period. These patients did not require chemotherapy, radiation or surgery following the administration of dostarlimab. While a longer follow up period is needed to assess the duration of the response, the results are promising.
The trial highlights the importance of biomarker-driven therapy in stage II and III disease.
Bowel Cancer Australia Medical Director A/Prof Graham Newstead AM said, “if further trials confirm these encouraging results, for a subgroup of rectal cancer patients, immunotherapy could mean traditional and more intensive therapies such as chemotherapy, radiation and surgery may be omitted, and patients spared from serious side effects and long-term impacts such as pelvic scarring, loss of childbearing potential and permanent colostomy.”
Jemperli (dostarlimab) has been provisionally approved in Australia to treat recurrent or advanced mismatch repair deficient (dMMR) endometrial cancer, a decision based on promising results from preliminary studies.