P1-16-01: A Randomized, Double-Blinded, Controlled Study of Exemestane vs. Anastrozole for the First-Line Treatment of Postmenopausal Japanese Women with Hormone Receptor Positive Advanced Breast Cancer.
Authors: Masuda N , Iwata H , Ohno S , Rai Y , Sato Y , Ohsumi S , Hashigaki S , Nishizawa Y , Saeki T , Noguchi S 
Published: June 2012

Background The steroidal irreversible aromatase inhibitor (AI) exemestane (E), the non-steroidal reversible AI anastrozole (A) and tamoxifen (T) are approved for the first-line treatment of the postmenopausal women with hormone receptor (HR) positive advanced breast cancer (ABC) in Japan. Although there are some studies which compare the efficacy and safety of AIs and T in the first-line disease setting, the number of studies that compare efficacy and safety of AIs is limited. We conducted this multicenter, randomized, double-blinded non-inferiority study, to evaluate the time to progression (TTP) in HR positive ABC randomized to therapy with E or A.

Methods Patients (pts) who were ≥20 years [yrs], postmenopausal, ECOG PS ≤1 and had HR positive ABC that recurred after the adjuvant therapy or metastatic disease settings were eligible and randomized (1:1) to 25 mg/day of E or to 1 mg/day of A. Data were evaluated for non-inferiority of E compared to A defined as the upper limit of a two-sided 95% confidence interval (CI) of the hazard ratio (HR) of TTP being less than or equal to 1.25. The primary endpoint was TTP assessed by the independent radiological images review committee (RIRC). Secondary endpoints included TTP by investigator, time to treatment failure, overall survival (OS), objective response rate (ORR), clinical benefit rate, and safety.

Results A total of 298 pts from 58 sites were randomized to E (n=149; mean age: 63.4 yrs) or A (n=149; mean age: 64.0 yrs). The mean BMI for the E and A arms were 23.0 kg/m2 and 23.6 kg/m2, respectively. Six pts (2 pts in E arm, 4 pts in A arm) were excluded from the full analysis set due to lack of evaluation for anti-tumor response after study medication started.

Median TTP (as per RIRC) was 13.8 months (M) vs. 11.1 M for E vs. A, respectively (HR 1.007; 95% CI: 0.771−1.317). Median TTP (Investigator) was 13.8 M vs. 13.7 M for E vs. A, respectively (HR 1.059; 95% CI: 0.816−1.374). The median OS for A treated pts was 60.1 M, OS for E was not reached (as of data cut-off: December 8, 2010). ORR for E was 43.9% (95% CI: 35.3−52.8) and 39.1% (95% CI: 30.6−18.1) for A. Other analyses, including sub-population analyses are ongoing.

The incidence of treatment related adverse events (AEs) in E arm was 71.1% (n=106) and in A arm 59.7% (n=89); the AEs were mostly grade 1 and 2 in 61.7% (n=92) and 53.7% (n=80) of pts respectively. They were expected and manageable. Treatment related SAEs were similar in both groups: 6 (4.0%) in E arm and 5 (3.4%) in A arm. The most common AEs for E were hot flushes (22.1%), arthralgias (16.8%), musculoskeletal stiffness (11.4%) and γ-GTP increased (10.1%); in A arm, hot flushes (14.8%) and arthralgia (16.8%) were observed in &gt;10% pts.

Conclusions Although median TTP (RIRC) of E is slightly improved compared with that of A, the result of TTP did not meet the non-inferiority criteria. There were no significant differences found between E and A in ORR. Although AEs in E were numerically higher, the observed AE profiles were similar to those previously reported for E and A. This study shows that E is comparable to A in efficacy and safety.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-16-01.