Marshall S. Horwitz, MD, PhD

Seattle Cancer Care Alliance
UW Genetic Medicine Clinic
Associate Dean, Department of Medicine; Professor, Department of Pathology; Adjunct Professor, Division of Medical Genetics; Adjunct Professor, Department of Genome Sciences
University of Washington School of Medicine
“It’s rewarding to learn about my patients’ lives and help them and their families unravel complex medical problems through genetic testing.”
— Dr. Horwitz
Why do you focus on the genetics of blood-related cancers?

Early in my training, I met a patient in her 20s who was pregnant and had been diagnosed with acute myeloid leukemia (AML). She mentioned a family history of the disease, and as I dug deeper, it turned out that there were about a dozen people in her family who had had AML or similar diseases. Many of them had died very early in adulthood, which had devasting consequences on the family, both emotionally and economically. At the time, not a lot was known about the genetics of blood-related cancers like leukemia. The technology that would allow us to study it was just taking off. It was a problem I wanted to try and solve, because leukemia is such a life-altering diagnosis. I started this work in 1992 and continue it to this day. My lab, in collaboration with others in Seattle and around the world, has helped identify many of the genes that put people at higher risk for these types of cancers. 

How do you help patients?

When people get cancer, it’s common to ask, “Why me?” In most situations, we don’t have a good answer to that question, because the majority of cancers are not inherited. But for many cancers, including blood cancers, there are a small subset of people who pass down a gene or several genes from one generation to the next, which increases their risk of developing these diseases. It can feel very unlucky to find out that you have an inherited cancer or that you may be at higher risk for it. Yet this knowledge can help us design a screening, prevention and treatment plan tailored specifically for you. It’s rewarding to learn about my patients’ lives and help them and their families unravel complex medical problems through genetic testing.

Provider background

Specialty: Genetics

Cancer genetics, hereditary blood cancers

I am a physician-scientist who is board-certified in internal medicine and genetic medicine, a specialty that involves the diagnosis and management of hereditary disorders. For several years, my focus has been on cancer genetics. I work with patients to help them understand the inherited origins of their disease and to develop a personalized approach to prevention and treatment. At SCCA, I am an attending physician in the Hematologic Malignancy Genetics Clinic, which provides risk assessment and follow-up care for people who have hereditary blood cancers or who have a family history of these diseases. I also provide care at the Genetic Medicine Clinic at UW Medical Center - Montlake and direct the UW School of Medicine Medical Scientist Training Program.

Similar to my clinical work, my research is also focused on hematological malignancies. I lead a lab at the UW Institute for Stem Cell & Regenerative Medicine that studies the genes and biological pathways that lead to these cancers.

Diseases treated

Education, experience and certifications
Undergraduate Degree
University of California, San Diego
Medical Degree
University of Washington School of Medicine
University of Washington, Internal Medicine
University of Washington, Medical Genetics
Board Certification
Internal Medicine, 1993, American Board of Internal Medicine; Clinical Genetics, 1996, American Board of Medical Genetics
PhD, University of Washington
NIH Director’s Pioneer Award

Dr. Horwitz received this award in 2007 from the National Institutes of Health. It supports researchers who are developing novel approaches to major challenges in the sciences.

Presidential Early Career Award for Scientists and Engineers

Dr. Horwitz received this award in 2002. Presented by the National Science Foundation, this award recognizes researchers and engineers who are committed to advancing the frontiers of science and show exceptional leadership potential.


Clinical trials

We make promising new treatments available to you through studies called clinical trials led by SCCA doctors. Many of these trials at SCCA have led to FDA-approved treatments and have improved standards of care globally. Together, you and your doctor can decide if a study is right for you.

Your care team

At SCCA, you receive care from a team of providers with extensive experience in your disease. Your team includes doctors, a team coordinator, a registered nurse, an advanced practice provider and others, based on your needs. You also have access to experts like nutritionists, social workers, acupuncturists, psychiatrists and more who specialize in supporting people with cancer or blood disorders.
Registered nurse (RN)
Registered nurse (RN)
Your nurse manages your care alongside your physician and assists with care procedures and treatments.
Patient care coordinator
Patient care coordinator
Your patient care coordinator works closely with you and your physician and serves as your scheduler.


SCCA accepts most national private health insurance plans as well as Medicare. We also accept Medicaid for people from Washington, Alaska, Montana and Idaho. We are working to ensure that everyone, no matter what their financial situation, has access to the care they need.