Adenocarcinoma with mixed subtypes is a rare but aggressive histologic subtype in colorectal cancer

Abstract Background: Though there have been studies investigating the clinicopathologic and prognostic relevance of mucinous adenocarcinoma (MAC) and signet-ring cell carcinoma (SRCC) compared with classic adenocarcinoma (CA), little is known about the prognosis of adenocarcinoma with mixed subtypes (AM) and the differences among these four subtypes. Methods: The statistics of colorectal cancer registered in the Surveillance, Epidemiology and End Results (SEER) database were retrieved and analyzed. We also compared the clinicopathologic and prognostic relevance between CA, SRCC, MAC and AM. Results: The frequencies of these four subtypes were 69.9% (CA, n=15,812), 25.1% (MAC, n=5,689), 3.6% (SRCC, n=814) and 1.4% (AM, n=321). All of MAC, SRCC and AM were significantly related with aggressive features. Only SRCC and AM were independent poor prognostic markers for overall survival by multivariate analysis. The malignancy degree of AM was between MAC and SRCC according to the clinicopathologic associations. The prognosis of AM was significantly worse than MAC but comparable with SRCC. Conclusions: We confirmed the clinicopathologic relevance with aggressive features of MAC and SRCC, as well as the poor prognostic relevance of SRCC by analyzing a large study population. Furthermore, we identified AM as a rare but aggressive histologic subtype in colorectal cancer, which particular attention should be given in clinical practice.