DNA sequencing method helps discover genetic cause of common breast tumors

A multidisciplinary team of scientists from the National Cancer Centre Singapore, Duke-NUS Graduate Medical School Singapore, and Singapore General Hospital has made a seminal breakthrough in understanding the molecular basis of fibroadenoma, one of the most common breast tumors diagnosed in women. The team used advanced DNA sequencing technologies to identify a critical gene called MED12 that was repeatedly disrupted in nearly 60 percent of fibroadenoma cases.

Related: DNA sequencing technologies: The next generation and beyond

"It is amazing that these common breast tumors can be caused by such a precise disruption in a single gene," says Tan Puay Hoon, a professor in Singapore General Hospital's Department of Pathology, who is one of the researchers who led the work. "Our findings show that even common diseases can have a very exact genetic basis. Importantly, now that we know the cause of fibroadenoma, this research can have many potential applications." The ability to measure the MED12 gene in breast lumps may, for example, help clinicians to distinguish fibroadenomas from other types of breast cancer, and drugs targeting the MED12 pathway may also be useful in patients with multiple and recurrent fibroadenomas, as this could avoid surgery and relieve anxiety, he explains.

The team’s findings have also deepened the conceptual understanding of how tumors can develop. Like most breast tumors including breast cancers, fibroadenomas consist of a mixed population of different cell types called epithelial cells and stromal cells. However, unlike breast cancers where the genetic abnormalities arise from the epithelial cells, the scientists, using a technique called laser capture microdissection (LCM), showed that the pivotal MED12 mutations in fibroadenomas are found in the stromal cells.

"Stromal cells function to provide a supportive tissue around organs and, in breast cancers, are typically thought of as uninvolved or at least secondary bystanders in tumor formation. Our study shows that far from that, fibroadenomas and possibly other tumors may actually arise from genetic lesions in stromal cells. Targeting such stromal cells may be an important avenue for therapy in the future," explains Steve Rozen, an associate professor in the Division of Neuroscience and Behavioral Disorders at Duke-NUS Graduate Medical School who helped to lead the work.

Reflecting its importance, the study also sheds light on the cause of uterine fibroids, another common benign tumor in women where similar MED12 mutations have been observed. "Combined with our data, the fact that MED12 mutations are shared, highly frequent, and specific to fibroadenomas and uterine fibroids strongly attests to a role for abnormal responses to female hormones in the birth of these tumors," says Patrick Tan, a professor in the Cancer & Stem Cell Biology Program at Duke-NUS Graduate Medical School, who also took part in leading the study.

The scientists are already planning subsequent studies to explore this possibility by investigating the role of MED12 in other types of breast tumors.

Full findings appear in the journal Nature Genetics; for more information, please visit http://dx.doi.org/10.1038/ng.3037.

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