Correlation of breast tumour aromatase activity and response to aromatase inhibition with aminoglutethimide

Tumour aromatase, oestrogen (E) and progesterone (P) receptor (R) measurements were carried out in biopsies from 29 patients with advanced or recurrent breast cancer. Patients were then treated with aminoglutethimide according to one of two dosage regimens: (a) aminoglutethimide 1000 mg/day + hydrocortisone 20 mg/day, and (b) aminoglutethimide 250 mg/day. Tumour aromatase values varied from 0.05 to 2.07 pmol ER produced/mg protein/h and ER and PR values from <1 to 249 and <1 to 132 fmol of steroid bound/mg protein, respectively. There was no correlation between aromatase values and either ER or PR and also no correlation between ER and PR and response to aminoglutethimide. Tumour aromatase values did however correlate with response to treatment. Mean aromatase levels for responders (1.18 ± 0.64 pmol E produced/mg protein/h) were significantly higher than those of non-responders (0.34 ± 0.27)(t = 5.20, DF 27; p<0.005). Ten out of fourteen patients with aromatase values>0.5 pmol ER produced/mg protein/h responded, whereas 0 out of 15 patients with tumour aromatase values less than this responded. Responses were seen at both dosages of aminoglutethimide. It is concluded that tumour aromatisation will be a useful measurement in predicting response to aromatase inhibitors.