Minority report - false negative breast assessment in women recalled for suspicious screening mammography: imaging and pathological features, and associated delay in diagnosis.

AIM: We studied imaging, pathology and diagnostic aspects of false negative assessment (FNA) in women recalled for suspicious screening mammography.
METHOD: Subjects were women aged 50-69 years undergoing biennial screening mammography within the Florence District screening programme from January 1992-December 2001 (339,953 consecutive screens). We identified all cancers occurring in women recalled to assessment and ascertained, and reviewed, all cases considered as negative on assessment and subsequently diagnosed with breast cancer. We compared imaging features, tumour histology and stage, and diagnostic testing on assessment for all women with cancer, and presentation and length of delay in women falsely negative on assessment.
RESULTS: Eleven thousand six hundred and twenty four women were recalled to diagnostic assessment (recall rate = 3.4%) predominantly for suspicious mammography (9,216 positive screens). Breast cancer was missed in 57 cases: a FNA rate of 0.50% (0.37-0.62%) and comprising 4.1% (3.0-5.1%) of cancers occurring in women recalled after a positive screen. Two types of abnormalities were significantly more frequent in FNA cases than cancers detected at assessment: mass with regular borders (21.1 vs. 5.6%, p = 10(-5)), and asymmetrical density (22.8 vs. 5.4%, p = 10(-5)). On review 56% of FNAs were benign or probably benign BI-RADS categories. FNA occurred in 1.4% of early recalls and in 0.4% of initial assessment (p=0.0001). Significantly fewer tests were performed when assessing missed cancers than detected cancers with the most significant difference noted for FNAC (29.8 vs. 96.0%, p=10(-6)); mammography as the only evaluation on assessment was more frequent in missed cancers (31.5% vs 0.2%, p = 10(-6)). The 57 missed cases were subsequently diagnosed at early recall (2 cases), next biennial screen (11 cases), or as interval breast cancers (44 cases) with a mean delay in diagnosis of 628 days. Tumour histology, size and nodal status did not significantly differ between cancers missed and cancers diagnosed on assessment.
CONCLUSION: False negatives on assessment represent a minority group in whom screening has failed. They might be reduced by adopting a more intensive diagnostic approach to assessment. Although there was no evidence of a worse prognosis in cancers missed at assessment, the delay in diagnosis is substantial and may impact long-term outcomes.