A widely used screening tool for colon cancer, sigmoidoscopy, misses precancerous growths in almost two-thirds of women - a disturbing failure rate twice as high as the one seen in men.

Colonoscopy - a more reliable but more expensive test than sigmoidoscopy- should now be considered the preferred method for most women.

Both colonoscopy and sigmoidoscopy involve the use of a long, flexible tube to inspect the twisting colon for precancerous growths, or polyps. But a colonoscope is longer and is used to examine the entire 6-foot length of the colon, while a sigmoidoscope inspects only the lower 2 feet or so.

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