Signet ring cell component predicts aggressive behaviour in colorectal mucinous adenocarcinoma

Mucinous adenocarcinoma (MAC) is defined by the presence of extracellular mucin covering more than 50% of the tumour area; however, MAC is histologically heterogeneous and some cases exhibit signet ring cell components. The aim of this study was to determine the prognostic impact of such variable morphology. A total of 299 consecutive MAC patients who underwent curative surgery were included. MACs were classified into four categories according to the predominant pattern of floating tumour cells: strips (27.1%), clusters (51.8%), signet ring cells (6.7%), and mixed clusters and signet ring cells (14.4%). In addition, we categorised MACs according to the relative amount of mucin. MACs with signet ring cell component were clearly associated with poor overall and recurrence-free survivals. Moreover, MACs with more than 50% signet ring cell component showed particularly poor clinical outcome just like non-mucinous signet ring cell carcinoma. MACs with a greater amount of extracellular mucin were associated with poor recurrence-free survival, independent of the pathological stage. In addition, lymphovascular and perineural invasion, advanced pathological stage, and old age at diagnosis were also prognostic factors for poor overall survival. MACs with more than 50% signet ring cell component should be classified as signet ring cell carcinoma and the presence of signet ring cells should be included in the pathology report of MACs with 10-50% signet ring cell component.