Is Mucinous Histology A Prognostic Marker In Early And Advanced Colorectal Cancer?

253 Background: In early and advanced colorectal cancer (CRC), there is limited data comparing the influence of mucinous (MAC) with non-mucinous adenocarcinoma (NMAC) histology on clinical outcomes. We investigated the association between histological type and outcomes in CRC. Methods: Medical records of patients with stage II, III and IV CRC referred to a tertiary centre in Western Sydney between 2009-2016 were examined and demographic and clinical information extracted. Key prognostic factors were modeled using log rank tests and proportional hazards (PH) regression methods in multivariate analyses. Results: Data on 686 patients was extracted. Median age was 70 years (19 – 94). Median follow up was 38.4 months. 98 patients (12%) had MAC and no differences in stage were observed at presentation between MAC and NMAC (p = 0.16). MAC was associated with increased prevalence of microsatellite instability (36% v 11% p < 0.01), high grade tumours (51% v 18% p < 0.01), female gender (61% v 45% p < 0.01) and right sided primary (65% v 40% p < 0.01). In stage II/III, MAC had comparable relapse free survival (RFS) versus NMAC (median 79 vs 97 months; P = 0.21). However, in the adjuvant chemotherapy group, a poorer RFS was seen for MAC (52 Vs 82 months, HR = 0.52, P = 0.03). In all patients with relapsed disease, MAC was more likely to be associated with peritoneal carcinomatosis (51% vs 26%; P < 0.01), and less likely to be associated with liver metastases (45% Vs 70%, P < 0.01) than NMAC. PH analysis of the MAC cohort revealed poorer RFS for LVI (HR 2.85; p = 0.03), T4 stage (HR 3.15, p = 0.01) and adjuvant chemotherapy (HR 5.49, p < 0.01). On multivariate analysis, T4 remained significant for poorer RFS. No differences were seen in OS in early stage CRC between MAC and NMAC. However, right sided and female gender with stage IV MAC had poorer OS (Right colon: HR 6.6; P = 0.03) (Female: HR 4.90, P = 0.03). Conclusions: MAC is associated with poorer RFS in early stage CRC irrespective of sidedness, and with poorer OS in right sided CRC. Given their poor response to adjuvant chemotherapy, novel adjuvant treatments should be considered for early MAC CRC. In the palliative setting, novel therapies and clinical trials are required for patients with MAC, particularly with right sided primaries.