Detection of P24 protein in human breast cancer: influence of receptor status and oestrogen exposure.

The expression of oestrogen regulated protein, P24, was investigated in 69 breast cancers. At initial evaluation P24 protein was detected significantly more frequently and was present in significantly higher concentration in oestrogen receptor positive than in receptor negative tumours. There was, however, no correlation between P24 staining and progesterone receptor, tumour ploidy or proliferative index. Nineteen patients received a short course of treatment with diethylstilboestrol. Following treatment with oestrogen, P24 staining became positive in 7/13 tumours previously negative for P24, including six tumours which were oestrogen receptor negative. Oestrogen administration also caused an increase of the proliferation index in 12/19 tumours, including 5/7 that were oestrogen receptor positive and 7/12 that were oestrogen receptor negative. In some instances oestrogenic stimulation of proliferation occurred together with increased P24 expression; in other instances proliferation index increased without induction of P24 synthesis. The in vivo effects of oestrogen in clinical breast cancer thus appear to show dissociation between enhancement of protein synthesis and cellular proliferation.