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Heather L. McArthur, MD, MPH

Medical Director, Breast Oncology
Cedars-Sinai Medical Center
Los Angeles, California
Conquer Cancer, the ASCO Foundation

Current Research

Goal: To identify combination strategies that more effectively treat patients with HER2-positive breast cancer.

Impact: Dr. McArthur is investigating methods of preventing recurrence in patients who have HER2-positive, early-stage breast cancer. Her findings could inform the development of new treatment combinations that extend long-term cure rates.

What’s next: She and her team will expand an ongoing study on the effectiveness of combining immunotherapy with chemotherapy plus HER2-directed therapy prior to surgery.

While major strides have been made in the treatment of HER2-positive breast cancer, 25 to 30 percent of patients with early-stage disease will experience a recurrence. One way to improve long-term cure rates may be to enhance treatment with the addition of immunotherapy. Dr. McArthur is testing chemotherapy and HER2-directed strategies with or without the immunotherapy drug pembrolizumab to determine if the addition of immunotherapy improves cure rates in women with HER2-positive breast cancer.

Full Research Summary

Research Area: Investigating the impact of adding immunotherapy to chemotherapy and HER2-directed therapy prior to surgery in HER2+ disease. 

Impact: Breast cancers driven by the HER2 protein represent approximately 20-25 percent of newly diagnosed breast cancers. The success of trastuzumab, a HER2-directed drug, has resulted in a nearly 50 percent reduction in the risk of distant metastases. Trastuzumab in combination with a second HER2 directed drug, pertuzumab, and chemotherapy can further reduce risk of recurrence. Despite these advances, more than one-quarter of women with HER2-positive, early stage disease will develop recurrence within ten years of diagnosis. Dr. McArthur is conducting studies on the effects of immune modulation combined with conventional HER2-directed therapy in hopes that combination strategies will confer a durable response and cancer-specific immunity. 

Current Investigation: Dr. McArthur and her colleagues are studying combination approaches to reduce the risk of recurrence in women with HER2-positive breast cancer. They are testing strategies of HER2-directed therapy and chemotherapy with and without immunotherapy. 

What she’s learned so far: Dr. McArthur has found that checkpoint blockade-mediated immunotherapy with the PD-L1 inhibitor, pembrolizumab, is synergistic when combined with HER2-directed therapy in laboratory models. They found pembrolizumab to be safe and modestly effective with trastuzumab in laboratory models of HER2-positive, trastuzumab-resistant metastatic breast cancer. Dr. McArthur and her colleagues have translated this work into a clinical study and will continue enrolling patients and adding more sites.

What’s next: The team will continue to expand their studies of combined immunotherapy and conventional HER2 directed strategies with a goal to reduce the amount of chemotherapy, and, to ultimately improve cure rates for affected individuals with life-long cancer-specific immunity.

Dr. McArthur is the recipient of an advanced clinical research award from Conquer Cancer, the ASCO Foundation similarly focused on immunotherapy approaches for breast cancer.


Heather McArthur, MD, MPH is Medical Director of Breast Oncology at Cedars-Sinai Medical Center. Dr. McArthur is a medical oncologist with a clinical practice dedicated to the care of patients with breast cancer. Her research activities are focused on innovations in the diagnosis and treatment of breast cancer, with a particular interest in novel immune therapy strategies. For example, she is currently evaluating the impact of tumor destruction with freezing (cryoablation) or radiation in combination with immune stimulation for the treatment of women with early stage breast cancer. It is hoped that by augmenting one's immune response to the unique biologic features of one's tumor, that an affected individual may develop long-term immunity against their tumor, and thus, be cured.

Dr. McArthur completed formal medical oncology training at the University of British Columbia. There, she was awarded the highly competitive Canadian Association of Medical Oncology/Canadian Institute for Health Research R&D Fellowship which funded an advanced clinical research fellowship at MSKCC. Thereafter, she joined MSKCC as faculty and in that role developed the institutional breast cancer immunotherapy program before joining Cedars-Sinai in 2016. She has a Master’s in Public Health with a focus on clinical trial design from Harvard University and has mentored many medical students, residents, fellows, and junior faculty in the conduct and reporting of several studies - two of which directly informed national (NCCN) treatment guidelines.

Dr. McArthur has designed, conducted, and reported on many studies in breast cancer and has held several leadership positions in the field including US Co-Chair of a Breast International Group Immunotherapy Taskforce, member of a NCI Breast Cancer Immuno-Oncology (IO) Working Group, member of a NCI Breast Cancer IO Task Force, and member of the Alliance for Clinical Trials in Oncology Immunotherapy/Immune Monitoring Working Group. She has served on the ASCO Conquer Cancer Foundation YIA/CDA Grant Selection Committee, the ASCO Breast Cancer Symposium Program Committee, and as a faculty member for the ASCO Annual Meeting Grant Writing Workshop. She is currently on the ASCO Annual Meeting IO Scientific Committee and participates in the ASCO Leadership Development Program. She has served as a reviewer for numerous journals including Science, the New England Journal of Medicine, and Cancer, and has authored more than 70 articles, review articles, invited commentaries, and book chapters on breast cancer. She serves on study numerous steering committees and is currently the co-PI for a large, randomized, international effort exploring adjuvant chemotherapy with or without immune therapy for the treatment of triple breast cancer (Impassion030).

McArthur headshot

BCRF Investigator Since


Donor Recognition

The LA Goes Pink Award in Tribute to Liz Smagala Tate

Area(s) of Focus