Fine-needle aspiration cytology in nonpalpable mammographic abnormalities in breast cancer screening: results from the breast cancer screening programme in Oslo 1996–2001

Fine-needle aspiration cytology (FNAC) of nonpalpable mammographic lesions has been under attack from two sides for some years. There has been much discussion and controversy as to the ability to differentiate between in situ and invasive carcinomas in cytological material. A further issue is that of optimal sampling to obtain adequate cell material in sufficient quantity. We present the results of FNAC from 832 nonpalpable mammographic abnormalities detected in the course of the breast cancer screening programme in Oslo during 1996–2001. In 11.6% of cases the smears were inadequate, and there were 7% false negatives (FN) and 1.3% false positives. Of the FN, 64% represented microcalcifications and 86% were due to sampling errors. Absolute sensitivity was 74%, complete sensitivity 88% and specificity 88%. In 255 carcinomas a cytological diagnosis of them as in situ or invasive was made. In 93% of the invasive cases (190/205) these had been correctly identified as invasive on FNAC. In 78% of cases proper follow-up could be resolved by cytology/radiology alone. Suboptimal sampling and localization remains the main cause of FN FNAC results. Problems in differentiating between in situ and invasive breast carcinomas can be significantly reduced by applying strict criteria for in situ lesions.