Novel Combo Boosts Response in HER2– Breast Cancer

Neil Osterweil

April 28, 2020

A novel combination has boosted responses in women with high-risk, HER2-negative breast cancer.

The new combo comprises the immune checkpoint inhibitor durvalumab (Imfinzi, AstraZeneca) and the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib (Lynparza, AstraZeneca).

When this combo was added to standard neoadjuvant chemotherapy, it yielded a significantly higher pathologic complete response (pCR) rate at the time of surgery than was seen with chemotherapy alone.

The superior pCR rate was seen across all HER2-negative breast cancer subtypes, including HER2-negative, estrogen receptor–positive tumors (Mammaprint high risk), and in women with triple-negative breast cancer (TNBC), reported lead investigator Lajos Pusztai, MD, DPhil, from Yale Cancer Center in New Haven, Connecticut.

"These results provide further evidence for the clinical value of immunotherapy in early-stage breast cancer and suggest new avenues for how to exploit these drugs in hormone receptor [HR]–positive breast cancers," said Pusztai.

He presented the results at the American Association for Cancer Research (AACR) virtual annual meeting, which took place online, owing to the COVID-19 pandemic.

Toxicities, Including Financial

"The benefits from immunotherapy are clearly emerging in early and metastatic triple-negative breast cancer, likely with PD-L1 expression. However, there's much more uncertainty in patients with hormone-sensitive tumors whether there is benefit and who will benefit from immunotherapy," commented Pamela N. Munster, MD, from the University of California, San Francisco, who was the invited discussant.

"The signal of a better pCR rate among patients in the ultra-high Mammaprint group may allow selection of patients with HR-positive disease who may benefit from immunotherapeutic agents and/or PARP inhibitors," she said.

Munster noted that the approximately 10% higher rate of immune-related adverse events of grade 3 or greater that was seen with the combination appears similar to that seen in other studies, but anemia and fatigue appeared to be less frequent with durvalumab/olaparaib and paclitaxel in comparison with paclitaxel alone.

"In the absence of a clear delineation of the contribution of olaparib, some weight should be given to the financial burden of adding both durvalumab and olaparib to a preoperative regimen," she said.

The additional cost of durvalumab is approximately $34,000, and adding olaparib boosts that by about $22,000 more, Munster said.

Ongoing Platform Trial

The new results come from one arm of the ongoing Investigation of Serial Studies to Predict Your Therapeutic Response Through Imaging and Molecular Analysis 2 (I_SPY-2) trial. This is an ongoing platform trial that is exploring the use of new drugs in combination with a standard neoadjuvant therapy backbone for the treatment of high-risk cancers.

In this trial, women with stage II or III breast cancer with tumors 2.5 cm or larger are assessed for one of eight biomarker subtypes according to HER2 status, HR status, and genetic risk factors, as determined on the basis of a 70-gene assay. The patients within each biomarker subtype are randomly assigned to receive standard therapy either with or without an investigational agent.

For each subtrial, a primary endpoint is an improvement in pCR in comparison with the standard of care.

Changes in tumor volume on MRI are used to predict whether patients will achieve a pCR. Those who are considered to have a high Bayesian predictive probability of success are eligible for moving on to phase 3 trials.

The I-SPY-2 trial was described in detail by principal investigator Laura J. Esserman, MD, MBA, from the Helen Diller Comprehensive Cancer Center at the University of California, San Francisco, in a 2017 interview from the annual meeting of the American Society of Clinical Oncology.

As previously reported by Medscape Medical News, the first drugs to "graduate" from the trial were the HER2/HER4 inhibitor neratinib (Nerlynx, Puma Biotechnology) and the investigational PARP inhibitor veliparib (AbbVie).

Study Details

The I-SPY-2 results that Pusztai reported at the AACR meeting were based on an analysis of 73 HER2-negative patients, including 21 patients with TNBC and 52 with HR-positive tumors with Mammaprint high-risk features. These patients underwent treatment with durvalumab 1500 mg every 4 weeks for three cycles, olaparib 100 mg twice daily for weeks 1 through 11, and paclitaxel 80 mg/m2 weekly for 12 weeks, followed by AC chemotherapy (doxorubicin and cyclophosphamide) for four cycles.

The 299 patients in the control arm received paclitaxel and chemotherapy only.

In all three biomarker subsets studied, durvalumab and olaparib increased pCR rates compared with controls, as shown in the table.

Table. Final pCR Probability by Biomarker Subset

Marker (No. of Patients) Estimated pCR Rate, Durvalumab/Olaparib Estimated pCR Rate, Controls
HER2– (73) 37% 20%
TNBC (21) 47% 27%
HER2–/HR+ (52) 28% 14%

 

The probability that the combination was superior to control in each subgroup approached 100%, Pusztai noted.

Adverse events with the combination were consistent with known side effects of the drugs, he commented. Immune-related grade 3 adverse events occurred in 19% of patients in the combination therapy arm, compared with 1.6% in the control arm.

Higher pCR rates were seen in the subset of immune-rich tumors among all cancer subtypes and in both study arms.

"Exploratory analysis suggests several potential predictive markers of durvalumab/olaparib benefit over chemotherapy alone," Pusztai reported.

These markers included Mammaprint MP2 (ultra high) vs MP1 in HR+/HER2 tumors, and low CD3/CD8 gene signature ratio, high macrophage/Tc-class 2 gene signature ratio, and high proliferation signature, all of which were associated with higher pCR rates in the experimental arm among patients with TNBC.

The trial was supported by the William K. Bowes Jr Foundation, Foundation for the NIH, Give Breast Cancer the Boot, UCSF, the Biomarkers Consortium, IQVIA, the Breast Cancer Research Foundation, Safeway, California Breast Cancer Research Program, Breast Cancer Research–Atwater Trust, and Stand Up to Cancer. Pusztai has received honoraria and consulting fees from AstraZeneca and other companies. Munster has received research and travel support from and has served on the scientific advisory boards of AstraZeneca and other companies.

American Association for Cancer Research (AACR) 2020: Abstract CT011. Presented April 27, 2020.

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