Basic characteristics and therapy regimens for colorectal squamous cell carcinoma

Colorectal cancer (CRC) is one of the leading causes of cancer-related death in males and females worldwide (1). The incidence and mortality of CRC both rank in the top five of all cancers in China (2). Adenocarcinoma makes up more than 90% of CRC (3,4). Surgery is commonly used as the primary therapeutic regimen, and the chemoradiation would also be closed in some cases with the consideration of staging, localization, and the patient's situation (5,6). There are several rare types of CRC tumors such as malignant carcinoid (1.5%), malignant lymphoma (0.6%), neuroendocrine carcinoma (0.3%), squamous cell carcinoma (SCC, 0.3%), and others (7). SCC is a small subset of CRC, accounting for less than 1% of CRC incidence (7,8). The incidence of rectal SCC (93.4%) is higher than colonic SCC (5.9%) (7). The most common site of SCC in the lower gastrointestinal tract is anal canal. Unlike SCC of the anal canal, colorectal SCC is much less reported. Most studies regarding colorectal SCC are limited to case reports, and the etiology is still unclear (9). There are varying hypothesizes about the etiology of colorectal SCC, such as differentiation of a pluripotent stem cell or the squamous metaplasia resulting from external irritation (10,11). Chronic inflammation or viral infection may also promote the development of colorectal SCC (9,12). However, the definite etiology of colorectal SCC remains to be discerned. Surgery was once the standard treatment for colorectal SCC, with tumor location and depth of invasion considered in operation selection (5,13). However, there is no distinct recommended treatment in the National Comprehensive Cancer Network guideline (3). In recent years, the treatment for SCC of the rectum and of the colon differs in that non-metastatic colonic SCC is only treated by surgery, while rectal SCC has the option of chemoradiotherapy with or without surgery or with surgery alone (14). Besides, there are few investigations about the treatment of the non-metastatic colonic SCC, which lacks the unified treatment standards