EP170 - Short Course Radiotherapy with and without delay; Effects on pathologic downstaging

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Purpose/Background: Since its inclusion in the NCCN guidelines in 2018, total neoadjuvant therapy has become the standard treatment for stage II and III locally advanced rectal cancer (LARC(. However, many cancer centers in the United States still follow varying practice guidelines regarding neoadjuvant chemotherapy and radiation protocols. Both long-course radiotherapy (LCRT) and short-course radiotherapy (SCRT) are effective treatment options for LARC. The choice of radiotherapy is made through a multidisciplinary approach, and this decision significantly impacts the timeline from diagnosis to surgical intervention.
The Stockholm III trial conducted in 2017 compared SCRT, SCRT with a delay, and LCRT with a delay. The findings suggested that a 4- to 8-week delay in surgery following SCRT is non-inferior to surgery performed within 1 week and may be a beneficial treatment strategy.
Our study seeks to determine whether delayed surgical intervention following neoadjuvant SCRT has any impact on downgrading of clinical T stage to pathological T stage in patients with locally advanced rectal cancer.

Methods/Interventions: We conducted a retrospective study conducted at Keck Hospital of USC between 2016 and 2024. We included all patients with locally advanced rectal cancer who received short course radiation with neoadjuvant chemotherapy followed by surgery. The time interval was defined as the duration between the last day of radiation and the date of surgery, with a time interval exceeding two weeks signifying a delay. The primary outcome measured was T stage downgrading. We also assessed whether there was an association between surgical delay and the administration of neoadjuvant chemotherapy.

Results/Outcomes: A total of 24 patients were included in the analysis. Among them, 9 patients (37.5%) experienced T stage downgrading from clinical to pathologic staging. 17 patients (70.8%) received TNT prior to surgery. We used logistic regression to examine the association between a delay in SCRT and T stage downgrading, controlling for the use of preoperative chemotherapy. All data was coded as binary variables.
The logistic regression model did not demonstrate a significant association between delay in SCRT and T stage downgrading odds ratio = 1.96, 95% CI [.070, 3.54]. Similarly, neoadjuvant chemotherapy was also not significantly associated with T stage downgrade odds ratio = 0.499, CI [.336, 11.503] (Table 1).
A total of 24 patients were included in the analysis. Among them, 9 patients (37.5%) experienced T stage downgrading from clinical to pathologic staging. 17 patients (70.8%) received TNT prior to surgery. We used logistic regression to examine the association between a delay in SCRT and T stage downgrading, controlling for the use of preoperative chemotherapy. All data was coded as binary variables.
The logistic regression model did not demonstrate a significant association between delay in SCRT and T stage downgrading odds ratio = 1.96, 95% CI [.070, 3.54]. Similarly, neoadjuvant chemotherapy was also not significantly associated with T stage downgrade odds ratio = 0.499, CI [.336, 11.503] (Table 1).

Conclusion/Discussion: Our findings indicate that a delay of 2 weeks or more from the last day of radiation to surgery does not impact T stage downgrading when compared to the immediate surgery group. These results were not influenced by whether the patient received neoadjuvant chemotherapy.