Scientists have identified the first genetic variant specifically associated with the risk of a difficult-to-diagnose cancer subtype, which accounts for approximately 10% to 15% of all breast cancer cases. The largest ever study of this breast cancer subtype, invasive lobular carcinoma, gives researchers important clues to the genetic causes of this particular kind of breast cancer, which can be missed through screening.
Invasive lobular carcinoma develops in the lobes of the breast that produce milk and can be particularly difficult to diagnose. The cancer often does not form a definite lump and may not show up on mammograms. As a result, women with this type of cancer tend to be diagnosed when the cancer is more advanced and more difficult to treat.
The research, published in PloS Genetics (2014; doi:10.1371/journal.pgen.1004285), was co-led by The Institute of Cancer Research, London, King’s College London, and Queen Mary University of London, in the United Kingdom. It used gene chip technology and complex statistical analysis to compare the DNA of more than 6,500 women with invasive lobular cancer with the DNA of more than 35,000 women without the disease.
A woman with the genetic variant rs11977670 was found to have a 13% higher chance of developing invasive lobular cancer than a woman without it. The variant is close to two genes on chromosome 7: BRAF, a known cancer-causing gene, and JHDM1D, which is involved in the activation and deactivation of other genes.
The discovery of the genetic variant, in conjunction with other markers, could help in the development of future genetic screening tools to assess women’s risk of developing invasive lobular cancer, and also gives researchers important new clues about the genetic causes of the disease and a related precursor to cancer called lobular carcinoma in situ.
As well as looking for new genetic risk factors, the researchers also evaluated 75 variants previously linked with breast cancer overall. They found that most of these were associated with risk of invasive lobular cancer specifically, as well as overall breast cancer risk.
The study also showed for the first time that genetic factors for invasive breast cancer can also predispose to lobular carcinoma in situ.
“We know invasive lobular breast cancers can behave differently to other breast cancer types, as well as be more difficult to diagnose—both of which led us to believe there may be different genetic factors in their development,” said Rebecca Roylance, MBBS, FRCP, PhD, of Queen Mary University of London. “It is really exciting that our theories based on clinical observations have been confirmed by the identification of specific genetic changes in patients with invasive lobular breast cancer.”