Population-based evaluation of adenosquamous carcinoma of the colon and rectum.

BACKGROUND: Information about adenosquamous carcinoma of the colon and rectum is scarce because of its extremely low incidence. OBJECTIVE: The aim of this study was to examine the prognostic significance of a histological diagnosis of adenosquamous carcinoma in comparison with adenocarcinoma of the colon and rectum. DESIGN: This study was retrospective in design. SETTING: California Cancer Registry data from 1994 through 2004 with follow-up through 2008 were analyzed. PATIENTS: Patients were included whose cancer of the colon and rectum, excluding the anus with a tumor histology of adenocarcinoma and adenosquamous carcinoma, was surgically treated. MAIN OUTCOME MEASURES: The primary outcomes measured were histology-specific survival analyses (with the use of the Kaplan-Meier method), and overall and colorectal-specific mortality (with the use of multivariable Cox proportional hazards regression analyses). RESULTS: A total of 111,263 adenocarcinoma and adenosquamous carcinoma of colon and rectal cancer cases were identified (adenocarcinoma, 99.91%; adenosquamous carcinoma, 0.09%). There was no significant difference in sex, age, race, and socioeconomic status between the 2 groups. The most common location of adenocarcinoma and adenosquamous carcinoma was the right and transverse colon. The adenosquamous carcinoma group was significantly associated with a higher rate of metastasis at the time of operation (adenosquamous carcinoma, 36.56% vs adenocarcinoma, 13.92%) and with poorly differentiated tumor grade (adenosquamous carcinoma, 65.96% vs adenocarcinoma, 19.74%) in comparison with the adenocarcinoma group. The median overall survival time was significantly greater in the adenocarcinoma group (82.4 months) in comparison with the adenosquamous carcinoma group (35.3 months). With the use of multivariable hazard regression analyses, adenosquamous carcinoma histology was independently associated with increased overall mortality (hazard ratio, 1.67) and colorectal-specific mortality (hazard ratio, 1.69) in comparison with adenocarcinoma. CONCLUSIONS: This is one of the largest studies of adenosquamous carcinoma of the colon and rectum to date. This uncommon colorectal cancer subtype was associated with higher overall and colorectal-specific mortality in comparison with adenocarcinoma. Among colorectal cancer cases, adenosquamous carcinoma histology should be considered a poor prognostic feature.