Micropapillary pattern in colorectal cancer: an Australian multicentre experience

Background: Colorectal cancer is the third most common cancer worldwide. Micropapillary carcinoma (MPC) is increasingly identified as a poor prognostic marker in various cancers, including breast, bladder and lung. It remains an under recognized subtype in colorectal cancer. The aim of this study is to evaluate the prevalence, implications and impact on survival of MPC in colorectal cancer in an Australian cohort. Methods: A retrospective review of all colorectal cancer resections in two tertiary centres in Sydney Australia was performed, between 2019 and 2024. MPC was identified on histolopathology as per standard guidelines of the resected specimens. Variables collected included age, sex, TNM, site, lymphovascular invasion (LVI), and lymph node involvement. Results: Of 597 colorectal cancer resections during the study period, 21 cases of MPC were identified (3.5%). Mean age was 60 years (SD 15 years). Twenty patients (95%) had T3-T4 tumours, 19 (90%) had positive lymph node involvement, 18 (86%) had confirmed or suspected LVI, and 4 (19%) had distant metastatic disease. Overall 1-year survival was 90% and 3-year survival was 76%. Conclusion: MPC is associated with high risk features in colorectal adenocarcinoma. Accurate histopathological diagnosis of these more aggressive cancers should guide prognostication, individualized adjuvant treatment and close surveillance.