Study Shows More Women With Advanced Breast Cancer Respond to Letrozole Than to Anastrozole

In an international study of the two leading aromatase inhibitors, datademonstrate that 50% more women with advanced breast cancer respond to letrozole(Femara) than to anastrozole (Arimidex); ie, more women treated with letrozoleachieved at least a 50% reduction in the size of their tumor. Data from thismulticenter, international study were presented at the 38th annual meeting ofthe American Society of Clinical Oncology (ASCO). The study enrolled 713postmenopausal women with estrogen-receptor (ER)-positive and/orprogesterone-receptor (PR)-positive or ER/PR status unknown breast cancer whowere receiving second-line treatment for advanced disease.

"It is becoming increasingly evident that aromatase inhibitors arechallenging and are likely to replace tamoxifen in the treatment ofpostmenopausal women with endocrine-dependent breast cancer," said CarstenRose, md, director, department of oncology, Universitetkliniken, OnkologiskaKlinik, Lund, Sweden, and lead investigator in the study. "Studies likethis are critical because they provide evidence to identify the aromataseinhibitor most likely to work best. The data in this trial show that more womenrespond to Femara than to Arimidex, which is important information forphysicians to consider when treating advanced breast cancer patients."

Second-Line Treatment

The investigation was conducted in 19 countries and compared the efficacy ofletrozole vs anastrozole in women with metastatic breast cancer followingfailure of antiestrogen therapy (eg, tamoxifen). The primary and secondary endpoints were time to disease progression, objective response rate, duration ofobjective response, overall clinical benefit, time to treatment failure, andsurvival. Patients were randomized to receive letrozole at 2.5 mg once daily oranastrozole at 1 mg once daily.

The data show that, based on objective response rate, 50% more womenresponded to letrozole than to anastrozole (19% vs 12%, P =.013). The completeresponse rate was 7% for letrozole vs 4% for anastrozole. No statisticallysignificant differences were seen in time to disease progression (primary endpoint) or other end points.

The data also show that the overall response rate in patients withsoft-tissue disease (ie, soft-tissue dominant, no bone or visceral involvement)was two times higher for women receiving letrozole than for women receivinganastrozole (37% vs 19%). In viscera-dominant disease (visceral involvement withor without bone and soft-tissue involvement), the overall response rate toletrozole was also higher than to anastrozole (14% vs 10%). There were nostatistically significant differences in any other end points.

Both letrozole and anastrozole were generally well tolerated, and theinvestigators found no statistically significant differences between arms in thefrequency of adverse events.

"The use of aromatase inhibitors is increasing and physicians needcompelling data by which they can make the right choice for the treatment ofbreast cancer," said David Parkinson, md, vice president, clinicalresearch, Novartis Oncology. "The consistent efficacy and overallperformance of Femara in the various clinical settings is extremely encouraging,and Novartis is looking forward to the results of the ongoing Femara adjuvantstudies."