Long-term outcomes and patterns of recurrence in mucinous rectal adenocarcinoma: A KCRG multicenter study.

Abstract

123 Background: Mucinous adenocarcinoma is a poor prognostic indicator of colorectal cancer. Due to its rarity, mucinous colon and rectal cancers are frequently analyzed together, and studies specifically addressing mucinous rectal adenocarcinoma are limited. Consequently, data on the clinical characteristics and prognostic factors contributing to poor outcomes remain scarce. Methods: Utilizing a multi-institutional database from KCRG 19 institutions, we conducted a retrospective analysis of patients with clinical stage II/III rectal cancer who underwent primary surgery between January 2018 and December 2022. Patients were categorized into mucinous rectal adenocarcinoma (MRA) and non-mucinous rectal adenocarcinoma (NMRA) groups for analysis. Patient characteristics, long-term outcomes, and recurrence patterns were compared between the groups. Results: Among the 1,311 patients, 42 (3.2%) were diagnosed with MRA and 1,269 (96.8%) with NMRA. In the MRA group, 21 patients (50%) presented with clinical T4 disease, compared with 353 patients (27.8%) in the NMRA group. Combined resection of adjacent organs was more frequently required in the MRA group (RD 11.3%, 95%CI −1.3 to 23.8), whereas the R0 resection rate was lower (RD −13.3%, 95%CI −24.6 to −2.0). The 5-year overall survival was significantly lower in the MRA group (71.5% vs. 84.6%; HR 2.63, 95% CI 1.35–5.26), and the 5-year recurrence-free survival was also lower (57.5% vs. 70.7%; HR 1.85, 95% CI 1.11–3.13). The 5-year cumulative incidence of peritoneal recurrence was significantly higher in the MRA group (12.1% vs. 2.9%, Gray’s test P=0.001), whereas no significant differences were observed in local recurrence (5.7% vs. 4.1%, P=0.480), liver metastasis, or lung metastasis. The median survival time after recurrence was 25.4 months in the MRA group compared with 52.9 months in the NMRA group. Conclusions: In this cohort, the incidence of local recurrence in MRA was not markedly high, suggesting that local disease control may have been achieved through advances in neoadjuvant therapy and surgical techniques. However, the high incidence of peritoneal recurrence and poor survival indicate that improving outcomes in MRA requires treatment strategies that address systemic recurrence, in addition to local control.