Saddle cancers of the colon and their progression to annular carcinomas.

Twenty-five cases of flat, ulcerating colonic carcinomas with heaped-up margins and central ulcerations were studied at various stages of growth. If not found at an early stage, a flat carcinoma will progress to an annular carcinoma. A retrospective evaluation of 8 "negative" colon examinations revealed the tumor as a contour defect, often on only one view, 9 months to 7 years before actual radiographic diagnosis of annular carcinoma. The primary symptom in 21 of the 25 patients was bleeding and there was a high incidence of local and distant spread.