Progesterone receptor activity and the response to the first endocrine therapy in advanced breast cancer

The predictive value of the progesterone receptor activity (PgR) was studied in a group of 84 patients with estradiol receptor (ER) positive advanced breast cancer who received their first endocrine treatment (tamoxifen or ovariectomy), with special emphasis on the timing of the receptor analysis. All patients were treated at 1 center and receptor analyses performed in 1 laboratory. In the group of 27 patients with PgR analysis performed immediately prior to the start of treatment, 14 out of 18 PgR+ve and only 2 out of 9 PgR-ve patients responded (P less than 0.02). In contrast, when PgR was analysed greater than 6 months prior to the start of treatment, the response rates for PgR+ve and PgR-ve patients did not differ significantly: 55% vs. 33% respectively. With regard to quantitative rather than qualitative PgR data, PgR levels exceeding 100 fmol/mg protein irrespective of ER levels, are an excellent indicator of hormonal responsiveness with a response rate of more than 80%, even if PgR analyses are performed long before the start of treatment.