A short course of radiation therapy followed by neoadjuvant chemotherapy resulted in a clinical complete response (CR) in almost half of 90 patients with locally advanced rectal cancer, allowing the majority of responders to skip surgical resection, a retrospective study indicates.
Specifically, at a median follow-up of 16.6 months for living patients, the initial clinical CR was 48% overall.
“While we do not have enough follow-up yet to know the late side-effect profile of this regimen, our preliminary results are promising,” Re-I. Chin, MD, Washington University School of Medicine, St. Louis, Missouri, told Medscape Medical News in an email.
The study was presented at the virtual 2020 meeting of the American Society of Radiation Oncology (ASTRO).
“Certainly longer follow-up will be needed in this study but none of the observed patients to date has experienced an unsalvageable failure,” said meeting discussant Amol Narang, MD, of Johns Hopkins University, Baltimore, Maryland.
He reminded conference attendees that despite good evidence supporting equivalency in oncologic outcomes between short-course radiation and long-course chemoradiation, the former is “highly underutilized in the US” with a mere 1% usage rate between 2004 and 2014.
The current study’s short-course treatment approach was compared in this setting to long-course chemoradiation and adjuvant chemotherapy in the RAPIDO trial reported at the 2020 annual meeting of the American Society of Clinical Oncology (ASCO), Narang pointed out.
Short-course patients had a higher rate of pathological complete response (pCR) and a lower rate of treatment failure compared with patients who received long course chemoradiation and adjuvant chemotherapy; both patient groups underwent total mesorectal excision — which is different from the current analysis. The RAPIDO investigators concluded that the approach featuring the short-course “can be considered as a new standard of care.”
Narang said the data collectively “begs the question as to whether the superiority of long course chemoradiation should really have to be demonstrated to justify its use.”
But Chin highlighted toxicity issues. “Historically, there have been concerns regarding toxicity with short-course radiation therapy since it requires larger doses of radiation given over a shorter period of time,” Chin explained. “But [the short course] is particularly convenient for patients since it saves them more than a month of daily trips to the radiation oncology department.”
Seven Local Failures
The single-center study involved patients with newly diagnosed, nonmetastatic rectal adenocarcinoma treated with short course radiation therapy followed by chemotherapy in 2018 and 2019. Nearly all (96%) had locally advanced disease, with either a T3/T4 tumor or node-positive disease. Median tumor size was 4.6 cm.
“Many of the patients in the study had low lying tumors,” Chin reported, with a median distance from the anal verge of 7 cm.
Radiation therapy was delivered in 25 Gy given in five fractions over 5 consecutive days, with the option to boost the dose to 30 Gy or 35 Gy in five fractions if extra-mesorectal lymph nodes were involved. Conventional 3D or intensity-modulated radiation was used and all patients completed treatment.
The median interval between diagnosis of rectal