Ethinylestradiol is beneficial for postmenopausal patients with heavily pre-treated metastatic breast cancer after prior aromatase inhibitor treatment: a prospective study.

BACKGROUND

Oestrogens usually stimulate the progression of oestrogen receptor (ER)-positive breast cancer. Paradoxically, high-dose oestrogens suppress the growth of these tumours in certain circumstances.

METHODS

We prospectively examined the efficacy and safety of ethinylestradiol treatment (3 mg per day oral) in postmenopausal patients with advanced or recurrent ER-positive breast cancer who had previously received endocrine therapies, especially those with resistance to aromatase inhibitors.

RESULTS

Eighteen patients were enrolled with the median age of 63 years and the mean observation time of 9.2 months. Three cases withdrew within 1 week due to oestrogen flare reactions with nausea, fatigue and muscle-skeletal pain. The response rate was 50% (9 out of 18), and the clinical benefit rate was 56% (10 out of 18). The stable disease (<6 months) was 17% (3 out of 18) and another 2 cases were judged as progressive disease. Time-to-treatment failure including 2 on treatment was a median of 5.6 months (range 0.1 to 14.5(+)). Although vaginal bleeding or endometrial thickening was observed in patients receiving long-term treatment, there were no severe adverse events, such as deep venous thrombosis or other malignancies.

CONCLUSION

Although the mechanism of this treatment has not been fully understood, our data may contribute to change the common view of late-stage endocrine therapy.