Abstract
Simple SummaryTumors of colon and rectum other than adenocarcinomas represent a neglected issue from clinical and laboratory points of view because of their rarity. In this review, we summarize and describe the rare histologic entities occurring in colon and rectum. Clinical and pathologic characteristics, prognostic behavior, treatments, and altered genes are reported to provide readers with a paramount and comparative perspective. In relation to this, we propose that improvements in registries and multidisciplinary research are warranted to ameliorate their management.The most frequent form of colorectal cancer is represented by adenocarcinoma being about 98% of tumor histological types. However, other rare histotypes can be found in colon and rectum (adenosquamous, goblet cell adenocarcinoma, lymphoma, medullary carcinoma, melanoma, mesenchymal, neuroendocrine, plasmacytoma, signet ring, squamous tumors). Altogether, these forms account for less than 2% of colorectal tumors. There are no specific diagnostic or therapeutic recommended approaches and most of the information available from literature derives from small and retrospective clinical series. In the present study, we provide a paramount and updated view on clinical and biologic characteristics of rare colorectal tumors.
Highlights
Colorectal cancer (CRC) is the third leading cause of cancer-specific death
We reviewed all the rare forms of CRCs so far described in literature with a potential diagnostic and clinical impact in the oncological practice in order to provide a paramount view on their clinical characteristics and to give an updated descriptive focus on their molecular characteristics
The search was performed in August 2021 with the terms “colorectal tumors” OR “colon” OR “rectum” AND “rare tumor” OR “rare histotype”
Summary
Colorectal cancer (CRC) is the third leading cause of cancer-specific death. It has been estimated that, in 2018, there were 1.8 million new cases of CRC in Western countries. The most frequent form of CRC is represented by (classical and mucinous) adenocarcinoma with three grades of differentiation: well, moderate, poor [1]. 98% of tumor histological types (about 1,764,000 cases) being moderately differentiated form the most frequently documented in the pathology reports (about 80%). Other rare histotypes can be found in colon and rectum (Figure 1) [2]. Even if probably underestimated (see beyond), these forms account for less than 2% of colorectal tumors.
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