This AHRQ-funded study of cervical cancer screening results found a remarkably low incidence of missed malignancies. The authors analyzed Papanicolaou test results and the results of subsequent biopsies and found that the results were discordant in only 0.3% of cases, with most of these inconsistencies being clinically insignificant. Delayed diagnosis of cancer is a common cause of malpractice suits in ambulatory care. Although a prior study by Raab and colleagues found a higher overall error rate in anatomic pathology cancer diagnosis, this study documents that the US cervical cancer screening system appears to be very effective at preventing squamous cervical cancer. However, a systematic review of missed or delayed cancer diagnoses found that misdiagnosis of four common types of cancer—melanoma, as well as cancer of the breast, lung, or colon—remains common.