RESUMEN
OBJECTIVE: A prospective study to evaluate the confidence level and predictive value of the fine needle aspiration biopsy was performed in the Oncology Service, "Hospital 20 de Noviembre, ISSSTE", Mexico City. MATERIAL AND METHODS: The cases with a palpable breast tumor, histologically confirmed who presented from 1992 to 1994 were included. One aspirate was done in each patient and these were reviewed by the same pathologist. We determined sensitivity, specificity and predictive value of the test. Age, border characteristics, size and mobility of the tumor were evaluated by Bayesian analysis. RESULTS: From 213 aspirates, 199 were elegible for diagnosis, 98 (46%) had a diagnosis of carcinoma, 13 were acellular and one suggestive. The acellular diagnoses were considered negative and suggestive positive, for analysis purposes. Mean age and tumor size were: 46.6 years (range 14-90) and 3.7 cm. (range 1-13) respectively. Sensitivity (0.932), specificity (0.973) and positive predictive value (96.9%) were estimated. We observed a high probability of true positive [P(D+/T+)] > 0.8 results in patients between 40 and 60 years of age, irregular borders, size > 2 cm and fixed lesions. CONCLUSIONS: The test has a high confidence level and in presence of two or more of the clinical factors mentioned, definitive decisions regarding treatment could be taken, without need of histologic confirmation.