Phase 2 data show increased response with added atezolizumab for PD-L1–negative patients
In a second study known as ABSCG-52/ATHENE, researchers evaluated neoadjuvant atezolizumab in combination with dual HER2 blockade plus epirubicin for the treatment of patients with early HER2-positive breast cancer.
Heidi Splete/MDedge News
Dr. Gabriel Rinnerthaler
For most of these patients, the current standard of care is neoadjuvant dual HER2 blockade with trastuzumab (T) and pertuzumab (P) plus poly-chemotherapy, said Gabriel Rinnerthaler, MD, of the Salzburg (Austria) Cancer Research Institute, said in his presentation at the meeting. However, de-escalation of chemotherapy has been a major focus of research in recent years, and more research is needed on a combination of anthracyclines, such as epirubicin and idarubicin, and immune-checkpoint modulators.
In the phase 2 study, the researchers randomized patients with previously untreated, histologically confirmed HER2-positive early breast cancer (defined as a clinical prognostic stage cT1c–4a-d, N0-3, M0) in a 1:1 ratio to two 3-weekly cycles of a chemotherapy-free induction phase (part 1) with TP plus 1,200 mg atezolizumab (TP-A) or TP alone.
“We hypothesized that the additive effect of immune checkpoint inhibitors plus anti-HER2 therapy and chemotherapy would not be linear,” he said.
At the end of this period, all patients underwent four cycles of TP-A in combination with epirubicin (part 2). The primary endpoint was pCR (defined as absence of invasive cancer in the breast and axillary nodes, or ypT0/Tis ypN0) in the overall study population, and a pCR of 40% was considered a positive result.
A total of 29 patients were randomized to TP-A and 29 to TP alone in nine treatment centers in Austria. The study population ranged from 33 to 82 years, with a median age of 57 years. Most patients (72.4%) had hormone receptor (HR)–positive tumors; a total of 45 patients had stage IIA cancer, and 13 had stage IIB.
The primary endpoint of pCR occurred in 35 patients overall (60.3%). In a univariate analysis, the response rates were lower in HR-positive patients, in premenopausal patients, and in histologies other than NST (invasive carcinoma of no special type), Dr. Rinnerthaler said, but none of the differences were statistically significant, likely because of the small numbers in each group.
In an exploratory analysis of the ITT population with available PD-L1 data, the pCR was 69.2% for PD-L1–negative patients and 55.2% for PD-L1–positive patients.
“We observed the highest pCR rates in PD-L1–negative patients treated in the TP-A group and the lowest in PD-L1–positive patients treated with TP alone,” Dr. Rinnerthaler said.
No new safety concerns were observed during the study, Dr. Rinnerthaler noted. AEs of grade 3 or higher occurred in 17 patients (29.3%), including 9 in the TP-A group and 8 in the TP group. The most common AEs in both groups were nausea, diarrhea, and fatigue. No AEs of special interest of grade 3 or higher (defined as immune-related AEs, cardiac disorders, or infusion-related reactions) were observed.
The study findings were limited by the small sample size, but the resulting pCR rate of 60.3% was higher than the predefined threshold of 40% and supports additional research, said Dr. Rinnerthaler.
“For HER2-positive early breast cancer, a neoadjuvant chemotherapy de-escalation immunotherapy regimen with trastuzumab, pertuzumab, atezolizumab, and epirubicin is highly effective and safe and merits further investigation,” he concluded.
During a question-and-answer session, Dr. Rinnerthaler was asked why pCR increased in PD-L1 negative patients.
Previous data have shown that PD-L1 is up-regulated in certain tumors, and may serve as a surrogate for sensitivity, he said. In previous studies the additional effect of atezolizumab was seen in a PD-L1–negative group.
Dr. Rinnerthaler said he hopes to clarify this question when his research team reviews biopsy data from baseline and after the induction phase.