Fulvestrant for Aromatase-Inhibitor–Resistant Breast Cancer

Summary and Comment |
February 16, 2007

Fulvestrant for Aromatase-Inhibitor–Resistant Breast Cancer

  1. William J. Gradishar, MD

Treatment with fulvestrant might delay initiation of chemotherapy and its attendant side effects in a significant fraction of patients.

  1. William J. Gradishar, MD

For postmenopausal women with advanced, hormone receptor–positive breast cancer, many endocrine treatment options are available. Clinical practice guidelines have long recommended that endocrine therapy should be continued until disease becomes refractory, endocrine options are exhausted, or disease tempo and extent change appreciably. In the latter case, a switch to chemotherapy can be a better therapeutic strategy. Researchers now report the long-term results of a European phase II multicenter trial in which the efficacy and tolerability of fulvestrant (Faslodex), an estrogen-receptor antagonist, were evaluated in women with hormone receptor–positive tumors whose disease had progressed.

Two groups of patients were enrolled prospectively: 70 women whose disease was initially responsive to aromatase-inhibitor (AI) therapy (objective response or stable disease for ≥24 weeks; Group A) and 20 women with initially aromatase-inhibitor–resistant disease (no tumor regression or stable disease for <24 weeks; Group B). Patients were excluded if they had life-threatening visceral disease, histories of brain or leptomeningeal involvement, treatment with more than one regimen of chemotherapy for metastatic disease, or more than two prior endocrine treatments. In Group A, 84% of patients had received tamoxifen, toremifene, or goserelin as adjuvant or first-line therapy for metastatic disease; all but one patient had received AIs. In Group B, 89% of patients had received tamoxifen as adjuvant or first-line therapy for metastatic disease; all but one patient had received AIs. All patients in both groups received fulvestrant (250 mg intramuscularly every 28 days). The primary endpoint was clinical benefit (complete or partial response or stable disease for ≥24 weeks). Secondary endpoints were time to disease progression, time to treatment failure, and tolerability.

Clinical benefit was seen in 28% of patients in Group A and in 37% of those in Group B. The median times to disease progression in Groups A and B were 3.6 and 3.4 months, respectively. The median durations of clinical benefit in Groups A and B were 10.8 and 9.0 months, respectively. Fulvestrant was well tolerated in both groups; only three patients experienced grade 3 events (injection-site reaction, hot flashes, transient ischemic attack).

Comment

Multiple endocrine agents are effective for treating hormone-sensitive breast cancer. As AIs are used more widely as adjuvant and first-line endocrine therapies of choice for metastatic disease, the role of fulvestrant should be investigated. These data show that fulvestrant is a well-tolerated endocrine agent that can provide clinical benefit in about 30% of patients who were previously treated with AIs, regardless of whether they benefited from the AIs. Another pragmatic consideration and interpretation of these data is that fulvestrant can delay initiation of chemotherapy and its attendant side effects in a significant fraction of patients.

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