Gastrointestinal Cancer

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SU_1_2000 - Correlation Between Immune Status After Neoadjuvant Therapy and Complete Response Rate in Patients with Locally Advanced Rectal Adenocarcinoma

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Correlation Between Immune Status After Neoadjuvant Therapy and Complete Response Rate in Patients with Locally Advanced Rectal Adenocarcinoma
N. Agrawal1, A. Yalamanchali2, and T. Lautenschlaeger1; 1Department of Radiation Oncology, Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, 2Indiana University School of Medicine, Indianapolis, IN

Purpose/Objective(s): Pathologic complete response (pCR) after definitive neoadjuvant chemoradiation (nCRT) for locally advanced rectal adenocarcinoma correlates with a favorable prognosis. The aim of this study was to identify routinely collected pre-surgical variables that correlate with pCR in patients undergoing definitive nCRT prior to surgical resection, with an emphasis on immunologic variables.

Materials/Methods: This was a registry-based review of all patients with locally advanced (cT1/N1-2 or cT2-4/N0-2) rectal adenocarcinoma treated at a single institution from 2008 – 2017 with standard 5-FU or capecitabine based, conventionally fractionated nCRT followed by total mesorectal excision. Independent-samples t-test and Pearson's chi-squared test were used to correlate pre-surgical variables with pCR.

Results: 332 patients were identified by the Cancer Registry, of which 109 comprised the final sample size. The primary reasons for exclusion were no electronic medical record and non-standard neoadjuvant treatment. Median age was 56 years, and 56.9% of patients were male. 77.1% and 52.3% of patients had T3 and N2 disease, respectively (AJCC 7th edition staging). 58.7% of tumors were moderately differentiated. 45.9% of tumors were within 5cm of the anal verge. Median radiation dose was 50.4 Gy, and 24.8% of patients were treated with IMRT. Median duration of nCRT was 5.6 weeks, and median duration from nCRT to surgery was 8.9 weeks. The pCR rate was 19.3%. Baseline hematologic parameters that were associated with pCR included higher baseline WBC count (mean 7.67 vs 7.55 in patients with vs without pCR, p=0.046) and lower baseline platelet count (mean 270 vs 293 in patients with vs without pCR, p=0.039). Higher ANC:ALC at 4-8 weeks post nCRT was significantly associated with worse pCR (mean 5.98 vs 9.05 in patients with vs without pCR, p=0.022), as was the presence of grade 3 or greater lymphopenia (pCR rate of 7.1% vs 37.5% in patients with vs without grade 3 or greater lymphopenia, p=0.04). Non-immunologic factors that predicted for pCR included smaller gross tumor volume (GTV) and larger percent weight change during nCRT. Early grade 3-4 lymphopenia was significantly correlated with grade 3-4 lymphopenia at 4-8 weeks. The pCR rate was not significantly correlated with tumor grade and location, clinical stage, radiation technique (3D-CRT vs IMRT) or total dose, nCRT treatment duration, or duration from nCRT to surgery.

Conclusion: In patients with locally advanced rectal adenocarcinoma undergoing standard nCRT, baseline WBC and platelet count, 4-8 week ANC:ALC, and 4-8 week grade 3-4 lymphopenia were all associated with pCR. Further research is needed to validate post-nCRT immune status as a potential biomarker of response to neoadjuvant therapy for rectal cancer.

Author Disclosure: N. Agrawal: None. A. Yalamanchali: None. T. Lautenschlaeger: None.

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