Colonic micropapillary carcinoma,a recently recognized subtype associated with histological adverse factors: clinicopathological analysis of 15 cases

Aim Micropapillary carcinoma (MPC) is regarded as an aggressive variant of adenocarcinoma in any location. The reported proportion of a micropapillary carcinoma component in an entire tumour ranges from 5 to 95% and only one case of pure MPC has been reported. To date, approximately 130 cases of MPC in the colorectum have been reported, but it is likely that this small number is to some extent due to under‐reporting because this pattern is not well recognized by the general pathologist. All previous studies have combined colonic and rectal primary tumours and most have only analysed patients with clinical Stages I or II. Method We analysed 15 cases of MPC of the colon alone, diagnosed in our institution, and compared them with 105 conventional carcinomas of the colon. Results An MPC component was present in 10% of all colonic carcinomas. These tumours presented at a median age of 56 years, and all were of American Joint Committee on Cancer Stages III and IV. Subserosal tissue invasion was present in every case, 60% had more than four positive lymph nodes, 60% were accompanied by poorly differentiated conventional carcinoma, 40% had had an incomplete resection and a third demonstrated lymphovascular invasion. Despite these adverse prognostic factors, tumours containing MPC showed the same survival, stage by stage, as conventional adenocarcinoma in multivariate analysis, although 3‐year survival (81.7%vs 87.3%, P = 0.035) was worse on univariate analysis. Conclusion The histopathologist should be aware of the possibility of MPC. Three‐year survival is worse than in patients with conventional colonic carcinomas in Stage III.