It may not be always necessary to approach the treatment of HER2-positive, hormone receptor–negative (HER2+/HR–) early breast cancer with added chemotherapy, survival results of a prospective multicenter randomized trial suggest.
In the ADAPT-HER2+/HR– trial, comparing a de-escalated 12-week neoadjuvant regimen consisting of dual HER2 blockade with trastuzumab (Herceptin) and pertuzumab (Perjeta) with or without weekly paclitaxel, the three-drug regimen was associated with high pathologic complete response(pCR) rates and excellent 5-year survival, irrespective of whether patients received additional chemotherapy, reported Nadia Harbeck, MD, PhD, of the University of Munich.
“Chemotherapy-free regimens are promising in highly sensitive tumors with early response, but future investigation of such chemotherapy-free regimens need to be focused on selected patients, like those with HER2 3+ tumors, non–basal-like tumors, those showing early response to the de-escalated therapy, and those with predictive RNA signatures such as immune signatures,” she said in an oral abstract session during the American Society of Clinical Oncology annual meeting (Abstract 503).
Under the WGS umbrella
The ADAPT HER2+/HR– trial (NCT01779206) is one of several conducted by the West German Study Group (WGS) on therapy for intrinsic breast cancer types.
In this study, 134 patients with HER2-positive, estrogen and progesterone receptor–negative tumors with no metastatic disease and good performance status were assigned on a 5:2 basis to neoadjuvant therapy with trastuzumab at a loading dose of 8 mg/kg for the first cycle followed by 6 mg/kg for subsequent cycles every 3 weeks x 4, plus pertuzumab at a loading dose of 840 mg followed by 420 mg every 3 weeks x 4 (92 patients), or to trastuzumab and pertuzumab at the same dose and schedule plus paclitaxel 80 mg/m2 once weekly for 12 weeks.
Patients had surgery within 3 weeks of the end of study therapy unless they did not have a histologically confirmed pCR, in which case they went on to receive standard neoadjuvant therapy prior to surgery.
Adjuvant therapy was performed according to national guidelines, although patients with a pCR after 12 weeks of study therapy could be spared from adjuvant chemotherapy at the investigator’s discretion.
Patients underwent biopsy at 3 weeks for therapy for early response assessment, defined as either a Ki67 decrease of at least 30% from baseline, or low cellularity (less than 500 invasive tumor cells).
First survival results
The investigators previously reported the primary pCR endpoint from the trial, which showed a rate of 90% after 12 weeks in the three-drug arm, and a “substantial and clinically meaningful” pCR rate of 34% after the trastuzumab plus pertuzumab alone.
At ASCO 2021, Dr. Harbeck reported the first survival data from the trial.
After a median follow-up of 59.9 months, there were no statistically significant differences between trial arms in either overall survival, invasive disease-free survival (iDFS), or distant disease-free survival (dDFS).
The 5-year iDFS rate in the three-drug arm was 98%, compared with 87% for the dual HER2 blockade-only arm, a difference that was not statistically significant.
The 5-year dDFS rates were 98% and 92% respectively. There were only seven dDFS events during follow-up, Dr. Harbeck noted.
There were only six deaths during follow-up, with overall survival rates of 98% in the paclitaxel-containing arm, and 94% in the anti-HER2 antibodies–only arm, a difference of one overall survival event, Dr. Harbeck said.