Reviewing interval cancers: time well spent?
OBJECTIVE
To categorize interval cancers, and thus identify false-negatives, following prevalent and incident screens in the Welsh breast screening programme.


METHODS
Breast Test Wales (BTW) Llandudno, Cardiff and Swansea breast screening units.


METHODS
Five hundred and sixty interval breast cancers identified following negative mammographic screening between 1989 and 1997 were reviewed by eight screening radiologists. The blind review was achieved by mixing the screening films of women who subsequently developed an interval cancer with screen negative films of women who did not develop cancer, in a ratio of 4 to 1. Another radiologist used patients' symptomatic films to record a reference against which the reviewers' reports of the screening films were compared. Interval cancers were categorized as 'true', 'occult', 'false-negative' or 'unclassified' interval cancers or interval cancers with minimal signs, based on the National Health Service breast screening programme (NHSBSP) guidelines.


RESULTS
Of the classifiable interval films, 32% were false-negatives, 55% were true intervals and 12% occult. The proportion of false-negatives following incident screens was half that following prevalent screens (P = 0.004). Forty percent of the seed films were recalled by the panel.


CONCLUSIONS
Low false-negative interval cancer rates following incident screens (18%) versus prevalent screens (36%) suggest that lower cancer detection rates at incident screens may have resulted from fewer cancers than expected being present, rather than from a failure to detect tumours. The panel method for categorizing interval cancers has significant flaws as the results vary markedly with different protocol and is no more accurate than other, quicker and more timely methods.
Gower-Thomas
Kate
K
Breast Test Wales, 18 Cathedral Road, Cardiff CF11 9LJ, UK.
Fielder
Hilary M P
HM
Branston
Lucy
L
Greening
Sarah
S
Beer
Helen
H
Rogers
Cerilan
C
D001943:Breast Neoplasms / Q000175:diagnosis*; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D008327:Mammography; D008403:Mass Screening / Q000379:methods*; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis*; D011237:Predictive Value of Tests; D011871:Radiology; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D013997:Time Factors; D014852:Wales