Although the data were ultimately inconclusive because of potential staging bias, the findings were “promising for recommending radiation omission in these patients,” Dr. Willett said.
The larger PROSPECT study published in The New England Journal of Medicine in 2023 was similarly encouraging, he said. In this trial, 1194 patients with locally advanced rectal cancer were randomized to FOLFOX or chemoradiation prior to sphincter-sparing surgery. The two groups showed similar 5-year estimated overall survival, complete resection (R0), and pathological complete response.
“These further data support the idea that we don’t need radiotherapy anymore,” Dr. Willett said.
PROSPECT was “a very well-done trial” that also showed important patient reported outcomes, he said. At 12 months after surgery, patients in the chemoradiation group had higher scores on fatigue and neuropathy measures, but less than 15% were severe. Sexual function scores for men and women were worse in the chemoradiation group, although overall health-related quality-of-life scores were not significantly different between the groups, he noted.
Does Dropping Everything But Immunotherapy Work?
Research is very preliminary, but a small study of 12 patients with mismatch repair-deficit (MMRd) locally advanced rectal cancer published in The New England Journal of Medicine “lends optimism” to a personalized treatment approach via a programmed death 1 (PD-1) blockade, Dr. Willett said. The “small, but impressive numbers” showed that all 12 patients treated with dostarlimab only (an anti-PD-1 monoclonal antibody) had durable disease control at a follow-up of 6-24 months.
This option is feasible for patients with MMRd locally advanced rectal cancer, Dr. Willett said in an interview. “Patients treated with only dostarlimab (a PD-1 inhibitor) had excellent outcomes and did not require radiation therapy, chemotherapy, and surgery. This is potentially a new paradigm of treatment for MMRd rectal cancer.”
What are the Clinical Implications and Next Steps?
Patients should be carefully evaluated and selected for treatment approaches by experienced multidisciplinary teams with vigilant posttreatment surveillance, including history and physical exam, endoscopy, computed tomography (CT) of the chest, and abdomen and pelvic magnetic resonance imaging (MRI), Dr. Willett said in the interview.
Data on the treatment of patients with MMRd rectal cancer using dostarlimab and other immune checkpoint inhibitors are preliminary; more patients and further follow-up are required, he said. This treatment is applicable to only 5%-10% of patients with rectal cancer, he continued.
“There is a need for biomarkers such as circulating tumor DNA to further aid in selection and monitoring of patients with rectal cancer,” Dr. Willett said.
Other preliminary research is examining circulating tumor DNA analysis to guide adjuvant treatment for patients with resected stage II colon cancer, he noted in his presentation. Currently, ctDNA-driven therapy is not recommended by the NCCN, but more research is needed to determine whether this strategy might be applied to decision-making in rectal cancer patients, especially with watch and wait/nonoperative strategies, he said.
What Are the Takeaways for Deintensifying Treatment of Rectal Cancer?
The global continuum of rectal cancer clinical trials has provided significant evidence that, for select patients, the deintensification of treatment strategies may result in the avoidance of radiation and even avoidance of surgery, which can profoundly improve long-term quality of life, Al B. Benson III, MD, said in an interview.