Among 843 cases of breast cancer, p53 oncoprotein was detected by the monoclonal antibody (MoAb) Pab-1801 in only 13%. Low-grade carcinomas (tubular, mucinous, papillary, and invasive cribriform types) did not express p53 protein, but it was observed in 4.2% of infiltrating lobular carcinomas (6 of 140 cases) and 50% of pure medullary carcinomas (5 of 10 cases). In intermediate-grade neoplasms, no correlation was seen between p53 status and other putative determinants of a poor prognosis. The latter included high tumor stage, lymph nodal involvement, high growth fraction (as determined by labeling with the MoAb Ki-67), negative results for estrogen receptor (ER) and progesterone receptor (PR) proteins, and amplification of the c-erbB-2 oncogene product in the neoplastic cells. Ninety-nine of 640 (15.5%) cases of high-grade, invasive, ductal breast carcinoma, however, showed an inverse relationship between expression of p53 protein and positive results for ER/PR proteins and a direct correlation with large tumor size, Ki-67-determined growth fraction, and amplification of c-erbB-2 oncopeptide. All of the latter associations were highly significant statistically. The authors conclude that mutant p53 protein may serve a prognostic role in a subset of cases of invasive ductal mammary carcinoma.

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