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PD-L1 expression best predicts response to atezolizumab + nab-paclitaxel for mTNBC



Programmed death-ligand 1 (PD-L1) expression on tumor-infiltrating immune cells is the best predictor of response to atezolizumab + nab-paclitaxel in patients with untreated metastatic triple-negative breast cancer, according to exploratory efficacy analyses of data from the phase 3 IMpassion130 trial.

The analyses of data for the 902 patients randomized to receive the PD-L1 inhibitor atezolizumab (Tecentriq) plus nanoparticle albumin-bound (nab)–paclitaxel or placebo plus nab-palcitaxel for the study also showed consistency between local and central estrogen-receptor, progesterone-receptor, and human epidermal growth factor–receptor 2 testing, Leisha A. Emens, MD, reported at the San Antonio Breast Cancer Symposium.

IMpassion130 is the first phase 3 study to demonstrate a benefit from [atezolizumab + nab-paclitaxel] in metastatic triple-negative breast cancer (mTNBC),” said Dr. Emens, professor of medicine in hematology/oncology, coleader of the Hillman Cancer Immunology and Immunotherapy Program, and director of translational immunotherapy for the Women’s Cancer Research Center at the University of Pittsburgh Medical Center.

She explained that progression-free survival (PFS) was significantly better in PD-L1–positive mTNBC patients treated with the atezolizumab + nab-paclitaxel, than in those who received placebo + nab-paclitaxel (hazard ratios in the intent-to-treat population, 0.8 and 0.62, respectively).

At the first interim overall survival analysis, a clinically meaningful improvement in OS was seen in PD-L1–positive patients in the treatment group (HR, 0.62; median OS improvement from 15.5 months with placebo to 25 months), she added.

In exploratory analyses, Dr. Emens and her colleagues sought to evaluate whether preexisting immune biology is associated with clinical benefit from atezolizumab + nab-paclitaxel, as has been demonstrated in studies of other agents that target the PD-1 pathway in other cancer types of cancer. They also assessed BRCA 1/2 mutation status as a biomarker for response.

“In patients enrolled on the IMpassion130 trial we found that PD-L1 in triple-negative breast cancer was expressed primarily on tumor-infiltrating immune cells,” she said. “In contrast to this, we found a very low rate of PD-L1 expression specifically on tumor cells across the patient population.”

Looking at both of those biomarkers together showed that a majority of patients with expression of PD-L1 on tumor cells were included in the PD-L1 immune cell–positive population, with only 2% having PD-L1 expression exclusively on their tumor cells.

Data previously reported at the European Society for Medical Oncology and published in the New England Journal of Medicine showed a PFS benefit, as well as a clinically meaningful improvement in OS of nearly 10 months, specifically in patients with PD-L1 immune cell–positive lesions treated with atezolizumab + nab-paclitaxel, she noted.

“In data presented for the first time today you can see that PD-L1–negative patients derive no overall survival benefit as there was no treatment effect with this therapy combination,” she said.

A trend was seen toward an association between immune cell positivity and poor prognosis, but this was not statistically significant, she said.

“Taken together, these data definitively show that PD-L1 immune cell positivity is predictive of both progression-free and overall survival benefit with atezolizumab + nab-paclitaxel,” she said.

She and her colleagues also looked at the level of PD-L1 expression in immune cells to assess whether there is a threshold that might be required.

“As long as there was a PD-L1 expression level of 1% or more in the immune cells, there was a significant progression-free and overall survival benefit for patients treated with atezolizumab + nab-paclitaxel. This suggests that this expression of over 1% will represent a threshold for identifying those patients who are likely to benefit from this combination,” she said.

Further assessment by CD8 T-cell status showed that patients who had CD8-positive T cells but who were PD-L1 immune cell negative had no benefit from atezolizumab + nab-paclitaxel, whereas those who were positive for both CD8 and PD-L1 expression on their immune cells derived significant PFS and OS benefit (HR, 0.89 and 0.77, respectively).

“So patients with CD8-positive tumors derive clinical benefit only if their tumors are also PD-L1-positive,” she said.

Similarly, no clinical benefit was seen in patients with stromal tumor-infiltrating lymphocyte (TIL)–positive tumors but who were PD-L1-negative, whereas those with stromal TIL-positive PD-L1–positive tumors derived significant PFS and OS benefit (HRs, 0.99 and 1.53, respectively), and this was also seen in the 15% of evaluable patients who had BRCA mutations.

“In patients who were BRCA mutated, but who were PD-L1 immune cell negative, there was no association of progression-free survival or an overall survival benefit [with atezolizumab + nab-paclitaxel]. In contrast, in patients who were BRCA mutated but PD-L1 immune cell positive ... there was an association with progression-free survival and a trend toward overall survival,” she said, noting that while the BRCA mutation findings are limited by small numbers, “they do show that mutations in BRCA and PD-L1 expression in immune cells are independent biomarkers; patients with BRCA1 or 2 mutations derive clinical benefit only if their tumors are also PD-L1 positive.”

“In this phase 3 IMpassion130 study, PD-L1 expression on immune cells is a predictive biomarker for selecting patients who benefit clinically during first-line treatment with atezolizumab + nab-paclitaxel for metastatic triple-negative breast cancer,” she concluded, adding that “patients with newly diagnosed metastatic and unresectable locally advanced triple-negative breast cancer should be routinely tested for their PD-L1 immune cell status to determine if they might benefit from the combination of atezolizumab + nab-paclitaxel.

IMpassion130 was sponsored by Hoffman-La Roche. Dr. Emens reported receiving royalties and consulting fees from several companies. She has contracts with Roche/Genentech, Corvus, AstraZeneca, and EMD Serono, and ownership in Molecuvax. She receives other support from DSMB and Syndax, and has received grants from Aduro Biotech, Merck, Maxcyte, and the Breast Cancer Research Foundation. She also reported serving as a member of the Food and Drug Administration Advisory Committee on Tissue, Cell, and Gene Therapies, and is a member of the board of directors for the Society of Immunotherapy for Cancer.

SOURCE: Emens L et al. SABCS 2018, Abstract GS1-04.

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