CHICAGO – HER2-positive/HR-negative breast tumors may have a different biology than HER2+/HR+ tumors and may derive more benefit from dual HER2 blockade, according to 5-year results from the phase III ALTTO trial comparing 1 year of adjuvant anti-HER2 therapy with lapatinib and trastuzumab alone, sequentially, or in combination in patients with HER2-positive early breast cancer.
The hazard ratios for this preplanned updated analysis at a median of 6.9 years of follow-up (when all patients had reached 5 years of follow-up) are similar to those from the primary analysis reported at the 2014 ASCO annual meeting and published in the Journal of Clinical Oncology in 2015 (J Clin Oncol. 2015;34:1034-42) at a median clinical follow-up of 4.5 years, Alvaro Moreno-Aspitia, MD, reported at the annual meeting of the American Society of Clinical Oncology.
In the current analysis, the rate of disease-free survival was 85% with combined lapatinib and trastuzumab (L+T), 84% for sequential trastuzumab and lapatinib (T–L), and 82% with T (hazard ratio for disease-free survival was 0.86 for L+T vs. T and 0.93 for T–L vs. T alone,) said Dr. Moreno-Aspitia of Mayo Clinic, Jacksonville, Fla.
“So, at this time, as noted in the primary analysis, there’s no benefit on the primary endpoint in regard to dual HER2 blockade as provided in this clinical trial,” he said.
There also were no significant differences seen in disease-free survival based on chemotherapy timing, he said.
Notably, disease-free survival was similar across treatment groups among patients with HER2+/HR+ tumors (85% for L+T, 85% to T–L, and 83% for T; HRs, 0.91 and 0.90 vs. T, respectively), but, among those with HER2+/HR– tumors, the 6-year disease-free survival difference for L+T (84%) vs. T (80%) was slightly greater (HR, 0.80).
“This is a hypothesis generating observation that also holds that possibly these patients with hormone receptor–negative tumors may derive benefit from dual HER2 blockade,” Dr. Moreno-Aspitia said, noting that this has also been observed in several other trials.
The 6-year overall survival in ALTTO was 93%, 92%, and 91% for L+T, T–L, and T, respectively (HRs for overall survival, 0.86 for L+T vs. T and 0.88 for T–L).
“At this time, there is absolutely no [overall survival] benefit on dual HER2 blockade over single agent trastuzumab. However, it is very rewarding to see that over 90% of the patients who participated in this trial are alive at this longer-term follow-up,” he said.
As for cardiac events, the numbers remained low as in the primary ALTTO analysis, and no new safety signals had emerged.
ALTTO study subjects were 8,381 patients randomized from 946 sites in 44 countries between June 2007 and July 2011. Those in the L+T group received both agents together for 52 weeks; those in the sequential treatment group received T for 12 weeks followed by a 6-week wash-out period, followed by lapatinib for 34 weeks; and those in the trastuzumab arm (the control arm) and the lapatinib arm each received treatment for 52 weeks. In 2011 the lapatinib arm was closed because of futility, and results for that arm are not included in this analysis.
Long-term follow up of participants continues, a large number of correlative studies are ongoing, and final results will be reported when all patients have been followed for at least 10 years, Dr. Moreno-Aspitia said.
The ALTTO trial was sponsored by GlaxoSmithKline and Novartis. Dr. Moreno-Aspitia reported having no disclosures.