B. Powers1,2, S. Felder1,2, I. Imanirad1,2, S. Dineen1,2 1Moffitt Cancer Center And Research Institute,GI Oncology,Tampa, FL, USA 2University Of South Florida College Of Medicine,Department Of Oncologic Sciences,Tampa, FL, USA
Introduction: Adjuvant chemotherapy (ACT) improves survival in curatively resected Stage 3 colon adenocarcinoma patients and is routinely recommended. However, the relative efficacy of ACT for histologic subtypes remains unclear, with some considering ACT less effective in those with mucinous histology.
Methods: Utilizing the National Cancer Database (NCDB), we identified patients with stage 3 colon adenocarcinoma undergoing curative resection (2004-2015). Patients with appendiceal, rectosigmoid, and rectal adenocarcinoma were excluded. The primary outcome was overall survival (OS). Multivariate Cox regression was performed to evaluate the impact of chemotherapy on OS while adjusting for demographic, anatomic and pathologic factors.
Results: A total of 109,688 stage 3 colon adenocarcinoma patients undergoing colectomy were identified, of whom 99,021 had follow-up for survival analysis. Patients with non-mucinous, mucinous, and signet ring cell (SRC) comprised 96,096 (86.7%), 12,297 (11.2%) and 2,295 (2.1%) of the study population, respectively. Receipt of ACT for stage 3 patients was similar between groups (70.8%, 69.5%, 68.3%, respectively). ACT significantly improved OS in all histologic subtypes. In univariate analysis, the Hazard Ratio (HR) for OS for non-mucinous tumors was 0.87, 95% (CI) [0.44-0.89], p<0.001, and for SRC, HR 1.71, CI [1.62-1.82], p<0.001. In multivariate analysis, there was no difference in OS between non-mucinous and mucinous stage 3 patients receiving ACT (p=0.87, CI [0.97-1.02]. The HR for SRC was 1.30, p<0.001, CI [1.22-1.38].
When stratified by histology, stage 3 patients with mucinous tumors who received ACT had decreased hazard of death compared to those who did not receive ACT, HR 0.41, CI [0.39-0.44]. Sidedness was not associated with survival in this cohort. Stage 3 patients with non-mucinous tumors receiving ACT also had decreased hazard of death compared to those patients who did not receive ACT, HR 0.35, CI [0.34-0.36]. In this cohort, patients with a left-sided tumor had a statistically significant decreased hazard of death compared to patients with right-sided tumors, HR 0.89, CI 0.87-0.91. On multivariate analysis, increased T and N stage, higher grade, Black race, increased age, and positive margin status were associated with a higher hazard of death for both histologies.
Conclusion: Non-mucinous and mucinous resected Stage 3 colon cancers treated with ACT demonstrated similar OS. Histologic subtype is an important factor in determining prognosis as SRC histology has significantly reduced survival compared to mucinous and non-mucinous subtypes. When stratified by histologic type, chemotherapy conferred a 65% and 59% improved survival for non-mucinous and mucinous tumors. The findings suggest that Stage 3 mucinous colon cancer realize a similar therapeutic benefit from ACT as those patients with non-mucinous colon cancer.