X. Gao1, P. Goffredo1, A. Kahl1, A. Beck1, M. Charlton1, I. Hassan1 1University Of Iowa,Iowa City, IA, USA
Introduction: Colorectal adenosquamous cell carcinoma (ASC) is an extremely rare histologic entity, representing <0.1% of all colorectal cancers. There are few data regarding its natural history and prognosis, most of which come from small institutional series and case reports. The aim of this study was to evaluate the presentation, treatment, and prognosis of colorectal ASC and compare it to colorectal adenocarcinoma (AC) and squamous cell carcinoma (SCC) in a large national database.
Methods: Patients diagnosed with colorectal AC, SCC, and ASC between 1973 and 2015 were identified from the Surveillance, Epidemiology, and End Results data. Patient, disease, and treatment characteristics were analyzed with chi-squared tests. Joinpoint regression was used to analyze cancer incidences. Cause-specific and overall survivals were calculated with Kaplan Meier curves.
Results: There were a total of 663,161 cases of which 0.07% were ASC and 0.4% were SCC. Since 2000, the incidences of colorectal AC and ASC have decreased while the incidence of SCC has increased (p<0.05). Among ASC patients, the mean age was 68 years, with 47% being male, and 81% White. Patients with ASC were more likely to present with higher T stage, positive lymph nodes, and metastatic disease than patients with AC or SCC (all p<0.001). For localized and regional disease, colon ASC was more frequently treated with major surgery (with or without chemotherapy and radiation), similar to colon AC and SCC. Rectal ASC appeared to have more variation in management strategies including different combinations of local excision, radical resection, chemotherapy, and radiation. In the colon, localized and regional ASC had an unadjusted 5-year cause-specific survival that was between AC and SCC while in the rectum, ASC had the worst survival. Metastatic colorectal ASC had the lowest cause specific survival compared to metastatic AC and SCC (Table 1).
Conclusion: Colorectal ASC presents at a more advanced stage compared to AC and SCC. For localized and regional ASC, survival patterns are different in the colon versus the rectum compared to the other two histologies. These outcomes might reflect differences in management approaches. The majority of colonic ASC were consistently treated with surgical resection, while a greater variability in treatment regimens was observed for rectal ASC. Standardizing the treatment of localized and regional rectal ASC based on radical resection with or without chemoradiation could improve survival.
