Missed cancers in screening colonoscopies

Sometimes people are diagnosed with colon or rectal cancer after undergoing a colonoscopy which was reported as negative for cancer, or after having polyps removed.  How can this be?  There are three possibilites:  missed lesions, incomplete polypectomy, and development of new cancers in patients without polyps.
Now a new study answers the question, and finds that more than half of cancers arising after negative colonoscopies or after colon polyp removal were the result of missed lesions.  Therefore this study highlights that the skills of the physician performing a screening colonoscopy are key.  Doctors should have cancer detection rates at or above the recommended thresholds.  Obviously, cancer detection is the most important quality measurement of screening colonoscopies.