What if one test could help your doctor chose exactly the right treatment for your breast cancer, or even match you to a clinical trial that might save your life? That's the promise of whole genome sequencing, an advanced form of genetic testing now showing remarkable results in a new study from the University of Cambridge.

The test will allow thousands of women every year to receive treatment precisely tailored to their unique cancer profile, the researchers say.

The hopeful study reveals how decoding the entire DNA of both a patient and her tumor can uncover the hidden genetic signature driving breast cancer. Instead of relying solely on where a tumor appears, or how it looks under a microscope, scientists can see what is driving its growth and how to stop it.

Genome sequencing has enormous potential for breast cancer treatment but is underused.

“Whole genome sequencing” is a high-tech process, but in simple terms, it's like taking a complete blueprint of the structure of the tumor. That genetic map shows mutations (errors in the DNA) that can help doctors predict which treatments will be most effective at stopping its growth and which might not work at all.

The researchers analyzed 2,445 breast tumors from 2,403 women treated at 13 NHS Genomic Medicine Centres across England. All participants were part of the national 100,000 Genomes Project run by Genomics England in partnership with the National Health Service.

Tracking medical outcomes over five years, the scientists searched for mutations that could influence breast cancer — especially those affecting how cells repair their DNA. They discovered that 27 percent of tumors carried genetic features that could immediately guide treatment or determine clinical-trial eligibility. This translates to more than 15,000 women a year in the United Kingdom who might benefit right now from genome testing.

Among the most important findings:

  • A DNA-repair problem — HRD or homology-directed repair deficiency — was found in about 12 percent of breast cancers.
  • Unique mutations that could be targeted by specific drugs.
  • Genetic signs of resistance to hormone therapy.
  • Patterns of potential vulnerabilities that new treatments could exploit.

Whole genome sequencing also helped the researchers predict which patients faced higher or lower risk. In the most common breast cancer subtype (E.R. +HER2), certain genetic markers, including mutations, are far more predictive of survival than traditional measures such as tumor grade or patient age.

Using this insight, the team designed a framework to help clinicians decide who might safely avoid aggressive therapy and who might need more. They estimate that 7,500 women with lower-grade tumors could benefit from stronger treatment plans.

The technology is now fast and affordable, with a complete human genome sequenced for about $100. The challenge lies in making sense of the sheer volume of information.

Serena Nik-Zainal from Cambridge's Department of Genomic Medicine and Early Cancer Institute led the study and emphasizes both the enormous potential and the current underutilization of genome sequencing, saying in a statement, “It is becoming increasingly possible to use whole genome sequencing to inform cancer management, but it's arguably not being used to its full potential, and certainly not for some of the more common types of cancer.”

The technology is now fast and affordable, with a complete human genome sequenced for about $100 she explained. But the challenge lies in making sense of the sheer volume of information. Fortunately, the UK's Genomic Medicine Service gives the NHS a head-start in applying this science to everyday care.

As Nik-Zainal noted, “We could massively open up the potential for recruitment, to multiple clinical trials in parallel — ultimately getting the right therapies to the right patients much faster.”

Ultimately, with genomic testing, the future of breast cancer care may lie not in treating patients the same way, but in finding the specific way to undermine its unique signature inside the body.

You can find the study in The Lancet Oncology.