Abstract
Competitive polymerase chain reaction assays have been developed for the quantitation of oestrogen receptor mRNA and two oestrogen-regulated mRNAs (progesterone receptor and pNR-2/pS2) in breast cancer cells. These assays are more sensitive than traditional hybridisation techniques, do not require the use of radioisotopes, measure absolute amounts of messenger RNAs and can be used to measure the expression of mRNAs in small numbers of tumour cells obtained by fine-needle aspiration (FNA). These assays should prove useful for predicting the hormone responsiveness of breast cancer from tumour cells obtained by FNA at diagnosis and could be particularly useful in the management of elderly/frail patients who receive primary tamoxifen, or in other patients for whom tumour tissue for standard biochemical measurements is not available.