Bacteria: An unexplored dimension of breast cancer
Specifically, they find that bacteria from the genera Bacillus and Staphylococcus, and from the family Enterobacteriaceae were able to mutate the DNA of the cells in the breast tissues and thus cause breast cancer.
Breast cancer is a family of malignancies in the tissues of the breast. Most commonly identified because of a lump in the breast, breast cancers usually progress from early stages, with mild symptoms like changes in the skin, nipple, or actual breast to late stages, with severe symptoms like nausea, jaundice, muscle weakness, and eventually death.
In 2013, more than 3 million women had breast cancer in the United States alone. And, in their lifetime, around 12 percent of women will be diagnosed with breast cancer.
On the other hand, in 2016, at least 200,000 new cases are expected while at least 40,000 will die from breast cancer.
Of all the risk factors for breast cancer, genetics seems to be the most dominant. Typically, mutations in the BRCA1 and BRCA2 genes are associated with breast cancer and can be inherited by the following generations. Other risk factors include diet, lifestyle, and race among others.
The research team has discovered another risk factor – the microbial population in the breast tissue.
In previous studies, it has been established that the breasts aren’t sterile; that is, bacteria live in the breasts. And, since the microbial population is closely related to other diseases like diabetes and asthma, the researchers explored whether the bacteria in the breast were associated with breast cancer.
For their study, breast tissues of 71 women between the ages 19 and 90 were collected. Among them, 58 were undergoing preventive or curative surgeries for tumours, while the rest were healthy and were undergoing breast operations for aesthetic purposes.
DNA later was extracted from all samples and sequenced to identify all the bacteria present. Finally, human cell cultures were infected with the bacteria present, and the damage to the DNA was assessed. Imaging and cell fluorescence methods were used to collect the data.
The research team found that tissues from breast cancer patients were enriched with bacteria from Enterobacteriaceae, Staphylococcus, and Bacillus taxa.
Concerning mechanisms, they found that Enterobacteriaceae and Staphylococcus bacteria were able to create double-stranded breaks (DSBs) in the DNA of breast cells. Since the inherent repair mechanism for these is error-prone, DSBs ultimately result in highly-mutated DNA and malignant cells.
While Bacillus bacteria weren’t observed to cause DSBs, they are known to convert progesterone, a growth hormone, to 5 alphapregnane-3,20-dione which is highly associated with cancer.
On the other hand, bacteria from the taxa Lactococcus and Streptococcus were significantly more abundant in healthy patients.
This, the researchers write, is because these bacteria can enhance the ability of immune cells which, potentially, can protect against cancer.
While requiring further studies, the researchers believe that their findings contribute to breast cancer research by identifying a new risk factor, and to drug development by determining a new potential target to harness. MIMS