AT ASCO 2017

CHICAGO (FRONTLINE MEDICAL NEWS) – Nine weeks of treatment with trastuzumab resulted in comparable disease-free and overall survival to that seen with the standard 12 months of trastuzumab – with about one-third of the rate of severe cardiac toxicity – in patients with HER2-positive early breast cancer in the Italian phase III multicenter Short-HER study.

The 5-year disease-free survival rate in 626 patients who received 9 weeks of trastuzumab was 87.5%, compared with 85.4% in 627 patients who received 1 year of trastuzumab therapy (hazard ratio, 1.15), Pier F. Conte, MD, reported at the annual meeting of the American Society of Clinical Oncology.

The upper limit of the 90% confidence interval (0.91-1.46) crossed the noninferiority margin set at 1.29 for this frequentist analysis, Dr. Conte of the University of Padova, Italy, said, noting that a subgroup analysis showed that patients with stage III disease and those with four or more positive lymph nodes – who together represented about 15% of the study population – had a disease-free survival advantage with longer treatment (HR, 2.30 and 2.25, respectively), and an interaction test was statistically significant.

However, a preplanned Bayesian analysis showed a 78% probability that the shorter treatment is not inferior to longer treatment for disease-free survival, he said.

The secondary endpoint of overall survival was also similar in the two groups (95.1% vs. 95.0%; HR, 1.06).

As for the secondary endpoint of cardiac events, the rate was 5.1% with shorter treatment vs. 14.4% with longer treatment. Grade 2 cardiac events occurred in 11.2% vs. 3.5% of patients in the treatment arms, respectively, and the grade 3 cardiac vents occurred in 2.7% vs. 1.1%, respectively. The rate of grade 4 events was 0.5% in both groups.

The overall difference between the groups with respect to cardiac events was highly statistically significant in favor of shorter treatment (HR, 0.32), Dr. Conte said.

Multiple studies have demonstrated the superiority of combining trastuzumab and adjuvant chemotherapy for HER2+ early breast cancer, and, following the release of some of those findings at the ASCO annual meeting in 2005, the agent was granted accelerated approval for this indication, Dr. Conte said.

“It was, however, clear that there were a number of reasons to believe that further investigation was appropriate on the optimal duration of trastuzumab duration,” he said, explaining that the same magnitude of benefit was reported by the small FinHER study with 9 weeks of trastuzumab and that clinical data suggest synergism of trastuzumab with chemotherapy.

“Finally, in the real world, there are patients at lower risk of relapse (more node-negative, more small tumors) and at higher risk of cardiac toxicity because of age or comorbidities,” he said. “So, the hypotheses behind the Short-HER [study] was that a shorter duration of trastuzumab administered concomitantly with chemotherapy might produce comparable efficacy with significantly lower toxicities and, of course, costs.”

Short-HER study subjects, who had a mean age of 55 years, had either HER2-positive, node-positive, or high-risk node-negative disease and were randomized to receive either the shorter treatment, including three courses of docetaxel given three times weekly plus trastuzumab given weekly for 9 doses, followed by three courses of 5-fluorouracil/epirubicin/cyclophosphamide, or standard 12-month treatment with four courses of anthracycline-based chemotherapy followed by four courses of docetaxel in combination with trastuzumab given three times weekly, followed by 14 additional courses of trastuzumab given three times weekly (for a total of 18 3-times-weekly doses). Radiation therapy was administered when indicated after chemotherapy, and hormonal therapy was started after completion of chemotherapy in patients with hormone-receptor–positive tumors.

Based on the frequentist analysis, noninferiority of the shorter treatment approach cannot be claimed, but, according to the preplanned Bayesian analysis, noninferiority is likely, Dr. Conte said.

“One year of trastuzumab is still standard. The Short-Her trial, however, reinforces the hypothesis that treatment deescalation retains efficacy with less toxicity. A shorter treatment might be an option for patients at low risk of relapse and/or higher risk of cardiac toxicity,” he said. “Moreover, these results might facilitate trastuzumab to patients in low/middle income countries.”

Individual patient meta-analysis with other trials testing different durations of trastuzumab administration is ongoing, he noted.

The Short-HER study was funded by the Italian Drug Agency, and drugs and insurance coverage were supplied by the National Health System. The study was sponsored by the University of Modena & Regio Emilia and the University of Padova. Dr. Conte has served on the speakers’ bureau for AstraZeneca, Lilly, Novartis, and Roche/Genentech and has received research funding and/or travel or other expenses from AstraZeneca, Celgene, and Novartis.