SAN ANTONIO (FRONTLINE MEDICAL NEWS) – The phase 3 SOLD trial failed to show a 9-week course of trastuzumab as noninferior to the standard 12-month course when combined with chemotherapy for women with early-stage HER2-positive breast cancer.

Disease-free survival (DFS) with a 9-week course of adjuvant trastuzumab (Herceptin)did not pass muster as noninferior to the standard 12 months, reported Dr. Heikki Joensuu , professor in the department of oncology at the Helsinki University Hospital and University of Helsinki.

“The non-inferiority of 9 week administration of trastuzumab plus docetaxel could not be demonstrated in terms of disease free survival, as compared to chemotherapy and one year duration of adjuvant trastuzumab.”

Based on these findings, he noted that chemotherapy plus one year of anti-HER2 therapy should remain the standard of care.

However, the dose of docetaxel administered along with trastuzumab could influence survival outcomes. Patients who received a higher dose of docetaxel in the 9 week cohort had similar DFS as those who received 12 months of trastuzumab.

Dr. Joensuu explained that the regimen of giving trastuzumab for one year is an arbitrary one and is not based on research data. In the four large randomized trials that established the current standard treatment for this population of breast cancer patients, trastuzumab was administered for one year and that eventually became the standard of care, he said at the San Antonio Breast Cancer Symposium.

But in two randomized trials that had relatively limited statistical power, a statistically significant difference in DFS or overall survival was not observed between patients who received only nine weeks of trastuzumab compared with those who received the one year regimen.

In addition, the one year treatment course is costly and has been associated with cardiac-related adverse events, although it is relatively uncommon (less than 3% of patients).

The phase 3 SOLD (Synergism or Long Duration) clinical trial was conducted by Dr. Joensuu and his colleagues to compare DFS between women treated with 9 weeks of concomitant trastuzumab plus docetaxel followed by 5-FU, epirubicin, and cyclophosphamide (FEC) to that of women treated with the same regimen followed by single-agent trastuzumab for a one year duration.

The cohort included 2,176 patients with early-stage HER2-positive breast cancer who were randomized to either the 9-week or the 12-month trastuzumab arm. In addition, cardiac function among women enrolled in the trial had to be normal, Dr. Joensuu said, as determined by left ventricular ejection fraction of 50% or greater.

Patients in both groups received three cycles of docetaxel (80 mg/m2 or 100 mg/m2) and trastuzumab three times a week, followed by three cycles of FEC. The dose of docetaxel was determined by the individual center. Patients in the 12-month arm continued to receive trastuzumab every 3 weeks for 14 cycles and in both groups, those with estrogen receptor–positive cancer received appropriate endocrine treatment per guidelines.

“SOLD was initially designed as a superiority trial,” he said, “But, we redesigned the study and the size during the study because we noticed that the assumptions we made for 5-year disease-free survival were too low.”

“We also realized that the shorter arm cannot be better than the longer arm because less drug is given,” said Dr. Joensuu. “So we changed it from a superiority trial to a noninferiority design, where the shorter arm would be at least equal to the longer arm.”

When looking at results, the DFS favored the longer arm: 90.5% in the 12-month arm vs. 88% in the 9-week arm (hazard ratio, 1.39; 90% confidence interval, 1.12-1.72). However, there were no substantial differences in secondary endpoints. Five-year distant DFS was 93.2% in the 9-week arm vs. 94.2% in the 12-month arm (HR, 1.24; 90% CI, 0.93-1.65), and similarly, 5-year overall survival was 94.7% vs. 95.9% (HR, 1.39; 90% CI, 0.98-1.89).

There was an interaction between the dose of docetaxel given concomitantly with trastuzumab. For patients who received 100 mg/m2 docetaxel, DFS was similar in both groups: 92.2% (long arm) vs. 87.8% (short arm) (HR 0.71, 90% CI 0,44-1.14). But among those who received 80 mg/m2 docetaxel, DFS was superior in the group who received 12 months of trastuzumab, compared with the 9-week group (91.3% vs. 86.8%; HR, 1.66; 90% CI, 1.30-2.11).

Less cardiac toxicity was observed in the 9-week group, for any protocol-defined cardiac adverse event (n = 22 [2%] vs. n = 42 [3.9%]; P = .012) and for heart failure (n = 21 [1.9%] vs. n = 36 [3.3%]; P = .046).

“Docetaxel dosing with trastuzumab requires further study,” Dr. Joensuu said.

SOURCE: Joensuu H et al., Abstract GS3-04