Summary: False negativity is one of the factors influencing the latening of the breast cancer diagnosis, even in the time of modern diagnostic methods and with good erudition and accurate complex examination. Time is the basic factor, influencing not only the radicality of treatment, but also its outcome. The stage of the disease is greatly influenced byt the time between first symptoms, finding of the diagnosis and beginning of the treatment. We found by analysing of 710 patients with breast cancer, that if the anamnesis was shorter than 3 months 82 % were stage I. If the anamnesis was longer than 6 months. 84 % were stage IV. In another group of 705 breast cancer patients, investigated in the faculty hospital, were 133 of cancers (19 %) initially false negative in the mammografical and cytological investigation. The most often misdiagnosis were fibrocystical mastopathy and fibroadenomas (82 %). The risk of false negativity was higher in younger women to 40 years. In women older than 50 years the risk declined. A smaller finding means more diffilcult diagnosis and higher risk. Such problems are showed even by another authors. The possibility of false negativity does exist even in lege artis examination in well equipped centres. It is necessary to keep this fact in mind and to try to decline its risk.
False negativity of the breast cancer
