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Heather L. McArthur, MD, MPH

Medical Director, Breast Oncology
Cedars-Sinai Medical Center
Los Angeles, California

Current Research

  • Seeking to improve treatments and outcomes for patients with metastatic breast cancer.

  • A clinical trial is planned to test the combination of immune modulation plus a short course of radiation in breast cancer patients.

  • These studies may lead to combination strategies to reduce resistance to immunotherapy and improve patient outcomes.

Patients with early-stage HER2-positive breast cancer have several treatment options. HER2-directed therapies plus chemotherapy has dramatically improved survival rates in what was once a lethal form of breast cancer. In spite of these advances, however, many women treated for early-stage HER2-positive breast cancer will ultimately experience a recurrence. Dr. McArthur is conducting studies to test combination approaches that include immunotherapy to achieve durable response and improve cure rates for women with HER2-positive breast cancer.

Full Research Summary

Approximately 20-25 percent of newly diagnosed breast cancers are HER2-positive. The successful development of trastuzumab, a drug that specifically targets the HER2 protein, has dramatically reduced the risk of metastasis in patients with early-stage disease. Dual HER2-directing (pertuzumab plus trastuzumab) in combination with chemotherapy can further reduce risk of recurrence in some affected individuals. 

Despite these therapeutic innovations, approximately 25-30 percent of women with HER2-positive early stage disease will develop a recurrence within 10 years of diagnosis. Thus, novel strategies are needed if long-term cure rates are to be improved. 

The focus of Dr. McArthur’s BCRF-supported research is to identify rational combination approaches to reduce the risk of recurrence for women with early-stage, HER2-positive breast cancer. 

One promising strategy is the addition of immunotherapy to the current standard of care in HER2-positive breast cancer. The rational for the approach is based on several factors. 1) Chemotherapy can induce cancer cell death resulting in the release of tumor fragments that are recognized by the immune system; 2) HER2-directed therapy acts synergistically with immune modulation and this combination approach may be exquisitely effective at harnessing the immune system; 3) Modern immunotherapy strategies can confer durable, long-term cancer control and this strategy could potentially provide life-long benefit to women with HER2-positive disease. 

Dr. McArthur’s team will study conventional chemotherapy and HER2-directed strategies with or without immune modulation (with a drug called pembrolizumab) prior to surgery in women with newly diagnosed, early stage HER2-positive breast cancer. They hope to demonstrate that the addition of immunotherapy will improve pathologic complete responses. Furthermore, it may allow for de-escalation (reduced dose or duration) of chemotherapy (and potentially HER2-directed therapy). 


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).

Large Researcher Headshot - McArthur Heather

BCRF Investigator Since


Donor Recognition

The LA Goes Pink Award in Tribute to Liz Smagala Tate

Area(s) of Focus