Analysis of the causes of false negative cytology reports on breast cancer fine needle aspirates

Forty-six (2.9%) false negative reports were recorded among adequate fine needle aspirates from 1609 consecutive histologically proven carcinomas, observed from 1991 to 1993. False negatives were more frequent among younger women (<40 years=7.1; 40-49 years=4.0; 50-59 years=3.6; 60-69 years=1.7; >69 years=1.5%), lobular invasive subtypes (5.4%), and smaller tumours (pT1a=4.2; pT1b=7.6; pT1c=1.9; pT2=2.1; pT3-4=1.5%). the latter finding is probably ascribable to better differentiation and less precise sampling of small non-palpable tumours. No significant association was found between the false negative rate and the sampler's or reader's skill and experience. the former finding may be ascribed to the wide use of sonography guided aspiration, even for palpable masses, and the latter to the fact that readers were highly experienced and undergo periodic quality control of individual performance. False negatives were reclassified at reviews as true false negatives, reading errors or inadequates in 27, 11, and eight cases, respectively. the observed findings suggest that in most cases cytological faults were due to the absence of cytological atypia in cells sampled from well differentiated tumours, rather than to misinterpretation or sampling from adjacent normal tissues.