07/24/2026
When Dr. Mary-Claire King began telling colleagues in the 1970s that breast cancer could be inherited -- that a single gene might be responsible -- her fellow scientists largely dismissed her ideas. The prevailing theory was that cancer was caused by viruses. The idea that genetic patterns could be linked to a complex disease like breast cancer struck most researchers as a dead end.
For much of the 17 years she spent hunting for proof, King worked in near-total obscurity testing hundreds of genetic markers by hand, one at a time. "No one noticed me," she later said of those years. Being overlooked, it turned out, gave her the freedom to chase a question no one else believed was worth asking.
Born in 1946, Mary-Claire King came to science through grief: at 15, she watched her best friend die of cancer. "I always hated cancer," she said. "It was a bad thing and I wanted to fix it."
She studied mathematics at Carleton College, then went to Berkeley for graduate school, where a single genetics course changed the trajectory of her life. During her doctoral work, she proved that humans and chimpanzees are 99% genetically identical -- a finding that reshaped evolutionary biology.
But it was cancer she kept coming back to. In 1990, after 17 years of painstaking research, King's team found a marker on chromosome 17 that was consistently co-inherited with breast cancer in severely affected families. She named the gene BRCA1 -- and in a single report, shattered the assumption that inherited genetics had nothing to do with complex diseases like cancer.
Women who carry harmful BRCA1 mutations face a lifetime breast cancer risk as high as 80%, compared to roughly 8% in the general population. For the first time, at-risk women could be identified before the disease developed. The discovery transformed cancer prevention, diagnosis, and treatment -- and the approach King pioneered has since been applied to heart disease, Alzheimer's, schizophrenia, and dozens of other conditions.
But King didn't stop at cancer. In 1984, a group of grandmothers in Argentina came to her for help. During the country's Dirty War, the military dictatorship had kidnapped up to 30,000 people -- many of them young parents whose infants were stolen and placed with families loyal to the regime.
The grandmothers, known as the Abuelas de Plaza de Mayo, had spent years traveling the world, asking any scientist who would listen whether there was a way to prove kinship when the parents were gone. They were met with shrugs -- until they found Mary-Claire King.
King developed a pioneering method using mitochondrial DNA, which passes unchanged from mother to child across generations, and created the Index of Grandpaternity -- a formula that could establish biological relationships with 99.99% certainty, even without the parents' DNA. It had never been done before. To date, her work has reunited 138 families.
Her forensic methods were later used to identify soldiers missing from Vietnam, Korea, and World War II, and to investigate human rights abuses in Bosnia, Rwanda, and Ethiopia. Her young colleagues from Argentina went on to form the United Nations Forensic Anthropology Team, which now carries out DNA identifications on six continents.
Of her approach to science and the years of doubt that preceded her breakthroughs, King once said: "Once your evidence is good, you really have to be very loyal to your own evidence. You have to be very, very critical of it. But once you're convinced you've got it, you can't cave."
She never caved. In 2014, she received the Lasker-Koshland Special Achievement Award in Medical Science. In 2016, President Obama presented her with the National Medal of Science. And in 2025, the National Academy of Sciences awarded her its Public Welfare Medal -- the Academy's most prestigious honor -- for demonstrating the power of science to serve humanity.
Today, at 80 years old, Dr. King is still publishing, still mentoring, and still pushing the boundaries of cancer genetics at the University of Washington. She showed the world that science is not just about discovery -- it is about what you do with it that matters.
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For children's books about female scientists whose research led to important health discoveries, we recommend "Never Give Up: Dr. Kati Karikó and the Race for the Future of Vaccines" (https://www.amightygirl.com/never-give-up), "June Almeida, Virus Detective" (https://www.amightygirl.com/june-almeida-virus-detective), "The Doctor With An Eye For Eyes" (https://www.amightygirl.com/doctor-eye), all for ages 5 to 9
For older kids, we recommend "The Code Breaker Young Readers Edition" for ages 10 and up at https://www.amightygirl.com/code-breaker-young-readers
There is also an excellent book about 21 trailblazing women in medicine and medical research, “Bold Women of Medicine" for ages 12 and up at https://www.amightygirl.com/bold-women-of-medicine
To inspire children and teens with stories of more trailblazing women of science who have made important discoveries, visit our blog post, "Ignite Her Curiosity: Children's Books to Inspire Science-Loving Mighty Girls," at https://www.amightygirl.com/blog?p=13914
And for two encouraging books about moms undergoing cancer treatment that were written to help kids understand what's happening during treatment, check out "Cancer Hates Kisses" for ages 3 to 7 (https://www.amightygirl.com/cancer-hates-kisses) and "Mama's Year with Cancer" for ages 4 to 8 (https://www.amightygirl.com/mama-s-year-with-cancer)
