Results of a Phase II Study Comparing Three Dosing Regimens of Fulvestrant in Postmenopausal Women with Advanced Breast Cancer (FINDER2)

The Faslodex Investigation of Dose evaluation in Estrogen Receptor-positive advanced breast cancer (FINDER)2 study evaluated the efficacy, safety, and pharmacokinetics (PK) of three fulvestrant dosing regimens. FINDER2 enrolled Western postmenopausal women recurring or progressing after prior endocrine therapy. Primary endpoint: objective response rate (ORR); secondary endpoints: time to progression (TTP), clinical benefit rate (CBR), tolerability, and PK parameters. Patients were randomized to receive fulvestrant: 250 mg/month (approved dose [AD]); 250 mg plus loading dose (loading dose [LD]; 500 mg on day 0, 250 mg on days 14, 28, and monthly thereafter); or 500 mg (high dose [HD]; 500 mg/month plus 500 mg on day 14 of Month 1). Treatment continued until disease progression or discontinuation. 144 patients were randomized: fulvestrant AD (n = 47); LD (n = 51); HD (n = 46). ORRs were: 8.5% (95% confidence interval [CI]: 2.4, 20.4%), 5.9% (1.2, 16.2%), and 15.2% (6.3, 28.9%) in the AD, LD, and HD arms, respectively. CBRs were: 31.9% (95% CI: 19.1, 47.1%), 47.1% (32.9, 61.5%), and 47.8% (32.9, 63.1%) for the AD, LD, and HD arms, respectively. Median TTP (months) was numerically longer for HD (6.0) and LD (6.1) versus AD (3.1). Tolerability was similar across dosing regimens. Steady-state plasma fulvestrant concentrations were predictable and achieved earlier with LD and HD. While there appeared to be a trend toward improved efficacy with HD and LD versus AD, no significant differences could be shown. A parallel study (FINDER1) has reported similar findings in Japanese patients.