UK primary-care referral guidance describes the signs, symptoms, and test results (“features”) of undiagnosed cancer. Guidance revision in 2015 liberalised investigation by introducing more low-risk features. We studied adults with cancer whose features were in the 2005 guidance (“Old-NICE”) or were introduced in the revision (“New-NICE”). We compared time to diagnosis between the groups, and its trend over 2006-2017.
Clinical Practice Research Datalink records were analysed for adults with incident myeloma, breast, bladder, colorectal, lung, oesophageal, ovarian, pancreatic, prostate, stomach or uterine cancers in 1/1/2006-31/12/2017. Cancer-specific features in the year before diagnosis were used to create New-NICE and Old-NICE groups. Diagnostic interval was time between the index feature and diagnosis. Semiparametric varying-coefficient analyses compared diagnostic intervals between New-NICE and Old-NICE groups over 1/1/2006-31/12/2017.
Over all cancers (N = 83,935), median (interquartile range) Old-NICE diagnostic interval rose over 2006-2017, from 51 (20-132) to 64 (30-148) days, with increases in breast (15 vs 25 days), lung (103 vs 135 days), ovarian (65·5 vs 100 days), prostate (80 vs 93 days) and stomach (72·5 vs 102 days) cancers. Median New-NICE values were consistently longer (99, 40-212 in 2006 vs 103, 42-236 days in 2017) than Old-NICE values over all cancers. After guidance revision, New-NICE diagnostic intervals became shorter than Old-NICE values for colorectal cancer.
Despite improvements for colorectal cancer, scope remains to reduce diagnostic intervals for most cancers. Liberalised investigation requires protecting and enhancing cancer-diagnostic services to avoid their becoming a rate-limiting step in the diagnostic pathway.

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