Estimating loss of the wild-type p53 gene by in situ hybridization of fine-needle aspirates from breast carcinomas

TP53 mutations have been found in 16-64% of breast carcinomas. The aim of o ur study was to investigate loss of the wild-type TP53 gene by in situ hybr idization (ISH) of fine-needle aspirates (FNAC) from breast carcinomas. The material consisted of FNAC from 33 breast carcinomas, with histologic spec imens from 19 of the cases. Routine diagnostic smears were used for cytolog ic grading. ISH of the wild-type TP53 gene and chromosome 17 was performed on air-dried smears. Hybridization signals were counted in at least 100 nuc lei, and the percentage for each signal number was calculated. FNAC from fo ur fibroadenomas as well as cell preparations from five lymphocyte cultures were used as normal/benign controls. Cutoff for defining loss of p53 gene signals was set at 20% of cells with zero and one gene signal only. Concomi tant p53 protein expression was determined on 20 histologic sections and ei ght additionally available air-dried smears. Loss of wild-type p53 gene was found in 20 carcinomas (60.6%). The rate of signal loss varied from 0.4% to 75.3% of the cells. All tumors with aneusom y of chromosome 17 revealed loss of p53 gene signals, as did 42% of the dis ome cases. Loss of wild-type p53 gene was present in 10 of 16 grade 1 cance rs (62.5%), eight of 13 grade 2 tumors (61.5%), and two of four grade 3 cas es. Signal loss did not correlate with p53 protein expression. In conclusion, subpopulations,with loss of the wild-type p53 gene are a com mon finding in breast carcinomas; they are detected in more than 60% of the tumors, including grade 1 cancers. Diagn. Cytopathol. 1999;20:266-270. (C) 1999 Wiley-Liss. Inc.