EP663 - Comparison of pathological complete response rates in locally advanced rectal cancer patients treated with SCRT vs LCRT undergoing TNT

Monday, May 12, 2025

8:10 AM – 8:15 AM PT

Location: Monitor 9, Sails Pavilion, Upper Level

ePoster Presenter(s)

Jordan Martucci, MD

Resident
University of Southern California/ Los Angeles General
Los Angeles, California, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.

Author(s)

Aubrey Swinford, MD

Resident
University of Southern California/Los Angeles General
South Pasadena, CA, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no financial relationships with ineligible companies.
LP

Lauren Polyakov, n/a

Medical Student
Keck School of Medicine
Los Angeles, California, United States

Disclosure information not submitted.
SW

Sabrina Woll, BA

Medical Student
University of Southern California
Los Angeles, California, United States

Disclosure information not submitted.
RS

Rishabh M. Shah, MS

Medical Student
Keck School of Medicine of USC
Cerritos, California, United States

Disclosure information not submitted.
Brian N. Williams, MD

Surgery Resident
University of Southern California
University of Southern California
Los Angeles, California, United States

Disclosure information not submitted.
JS

Joongho Shin, MD

Clinical Associate Professor
Keck Medicine of USC
Pasadena, California, United States

Disclosure information not submitted.
SB

Sacha Broccard, MD

Assistant Professor of Clinical Surgery
USC Keck Medicine
Los Angeles, California, United States

Disclosure information not submitted.

Senior Author(s)

Sang W. Lee, FASCRS

Professor and Chief of Colon and Rectal Surgery
USC Keck school of Medicine
Los Angeles, California, United States

All of the relevant financial relationships listed below have been mitigated.
This individual has no relevant relationships with ineligible companies.

All of the relevant financial relationships listed below have been mitigated.

Jordan Martucci, MD: This individual has no financial relationships with ineligible companies.

Aubrey Swinford, MD: This individual has no financial relationships with ineligible companies.

Sang W. Lee, FASCRS: This individual has no relevant relationships with ineligible companies.

Image or Table (Do Not add text here):

Purpose/Background: While total neoadjuvant therapy (TNT) is established as the standard of care for Locally Advanced Rectal Cancer (LARC), it is still uncertain which combination of neoadjuvant chemotherapeutics and radiation dosage is most effective. Multiple combinations of chemotherapy agents have been shown in clinical studies to increase outcomes either as induction or consolidation chemotherapy. Likewise, various options exist for radiotherapy, including short course radiotherapy (SCRT) and long course chemoradiotherapy (LCRT).
Our study investigates the differences in the rate of complete pathological response (pCR) among patients receiving SCRT or LCRT, with either induction or consolidation chemotherapy.

Methods/Interventions: This retrospective study was conducted at Keck Hospital of USC between 2016 and 2024. We included patients diagnosed with LARC who underwent TNT followed by surgical intervention. A comprehensive chart review was performed to determine which patients received SCRT with either consolidation or induction chemotherapy, or LCRT with either consolidation or induction chemotherapy. We examined oncology records to verify the specific chemotherapy regimen administered. Pathology reports were reviewed to identify patients who achieved pCR or having residual disease. The primary outcome of this study was to assess the likelihood of achieving pCR across the four treatment groups.

Results/Outcomes: A total of 73 patients were included in the analysis. 21 patients (28.77%) received SCRT and 52 (71.23%) received LCRT. 31 patients (42.47%) received induction chemotherapy, while 42 (57.53%) received consolidation chemotherapy. Pathological complete response (pCR) was achieved in 12 patients overall, with 4.5% of SCRT patients and 21.6% of LCRT patients achieved pCR.

We used a Chi-Squared test to compare pCR rates between the SCRT and LCRT groups. The results demonstrated a significant association in pCR rates, with LCRT showing a notably higher rate of pCR compared to SCRT (χ² = 4.490, p = 0.034; 26% vs. 4.5%). We also assessed the relationship between chemotherapy type (induction vs. consolidation) and pCR. We found no significant association (χ²=0.490, p=0.484) (Table 1).

Given the significant difference in pCR rates between patients receiving SCRT and those receiving LCRT with any form of TNT, we conducted another Chi-Squared test to examine the effects of chemotherapy type—induction versus consolidation—within both SCRT and LCRT groups on pCR rates. However, the analysis revealed no significant differences in pCR rates between groups (χ² = 3.389, p = 0.336).
Finally, we analyzed the relationship between treatment groups (SCRT + consolidation, SCRT + induction, LCRT + consolidation, and LCRT + induction) and lymph node yield using One-Way ANOVA. The analysis revealed no significant difference between the groups (F(3,1.523), p=.216).

Conclusion/Discussion: Our findings highlight the significant difference in pCR rates between patients receiving LCRT and SCRT, which supports prior research that LCRT is more effective in achieving pCR. However, the type of chemotherapy—induction versus consolidation—did not significantly influence pCR rates and lymph node yield within either treatment group.