The Impact of Adjuvant Chemotherapy on Survival in Mucinous and Non-mucinous Rectal Adenocarcinoma Patients After TME Surgery

Background: The value of adjuvant chemotherapy (CT) for rectal cancer patients is debated and varies in different subgroups. One such subgroup is mucinous adenocarcinoma (MAC), which is more treatment resistant compared to non-mucinous adenocarcinoma (NMAC). To date, mucinous histology is not taken into account when deciding on adjuvant treatment strategy. No previous study has exclusively included patients with RC, then separated MAC and NMAC and compared the survival in patients that had or did not have adjuvant CT. Methods: The study included retrospective data from 365 Swedish patients with stage II-IV rectal adenocarcinoma, 56 patients with MAC and 309 patients with NMAC. The patients had surgery with total mesorectal excision (TME) in a curative intent during 2004 -2013 and were followed up to 2021. Clinicopathological characteristics, and details concerning oncological and surgical treatment were recorded. Results: Patients with MAC that had adjuvant CT had better overall survival (OS) compared to patients without CT (HR 0.42; CI 95%: 0.19-0.93; p = 0.032). The difference was still significant even after adjusting for sex, age, stage, differentiation, neoadjuvant CT and preoperative radiotherapy (HR 0.40; CI 95%: 0.17-0.92; p = 0.031). There were no such difference in the NMAC patients. Conclusions: The patients with MAC benefited from adjuvant CT while patients with NMAC did not, indicating that the two subgroups of patients may need different treatment strategies.