Adenosquamous carcinoma of the colon, rectum, and anus: epidemiology, distribution, and survival characteristics

There have been 49 cases of adenosquamous carcinoma of the colon, rectum, and anus reported in the English literature. We have reviewed 145 cases of adenosquamous carcinoma to better define epidemiologic and survival characteristics of this extremely rare colon carcinoma.

The National Cancer Institute's Surveillance, Epidemiology, and End Results program public use CD-ROM file for the years 1973 through 1992 were reviewed. This represents approximately 9.5 percent of the United States population. Adenosquamous carcinomas arising in the colon, rectum, and anus were identified using the International Classification of Diseases-O codes. The Astler-Coller tumor classification was used for staging. Two-tailed Student's t-test, Mantel-Haenszel chi-squared tests, and generalized Wilcoxon's tests were used for comparisons of means, proportions, and actuarial survival rates, respectively. Survival curves were calculated by the Kaplan-Meier method.

One hundred forty-five cases of adenosquamous carcinoma were identified, representing 0.06 percent of all colorectal malignancies. The mean age of patients was 67 years. Eighty-four percent of patients were Caucasians, 15 percent were Afro-Americans, and 1 percent were other races. Afro-Americans were diagnosed at a significantly younger age (median age, 62 years; P = 0.03). Fifty-three percent of the carcinomas were located in the sigmoid colon, rectum, and anus, 28 percent in the right colon, and the rest in the middle segment. Seventy-four percent of distal cases were staged A through C, compared with 44 percent of proximal cases. Patients with adenosquamous carcinoma of the sigmoid colon, rectum, and anus survived longer than all other patients (P = 0.001). Patients with adenosquamous carcinoma Stages A and B1 had survival rates similar to patients with comparably staged adenocarcinomas. Fifty percent of the patients, including most of the patients with D stage, died in the first year. Patients with Stages B2, C, and D adenosquamous carcinomas had a significantly shorter survival than the comparably staged adenocarcinomas (P < or = 0.02). The overall adjusted five-year survival rate was 30.7 percent. In those patients who survived more than 24 months, the five-year survival was 84 percent.

The survival rates for patients with adenosquamous carcinoma Stages A and B1 are similar to patients with comparably staged colorectal adenocarcinomas. However, we found that patients with colorectal and anal adenosquamous carcinomas staged B2 through D have significantly poorer survival than patients with comparably staged adenocarcinomas, supporting the previous reports of a poor prognosis associated with adenosquamous carcinomas.