Degnim AC, et al., 2017

The normal mammary gland contains a mucosal (moist) immune system, as do other organs such as the lung and gastrointestinal tract. In the mammary gland, this immune system protects against infection, among other benefits. An impaired mucosal immune system, then, may cause chronic inflammation, which can lead to tumor formation.

Scientists have studied the immune system in breast cancer progression, but little is known about the role of the immune system in the earliest stages of breast cancer. Are there ways that supporting the immune system in the breast could lower risk of breast cancer, to prevent carcinogenesis (the formation of cancer)?

For this study, scientists used normal breast tissue samples from the Komen Tissue Bank and benign breast disease samples from the Mayo Clinic. People with benign breast disease are at an increased risk of developing breast cancer. Comparing the immune cells and other properties of the two types of samples could expose differences that may lead to insights about cancer formation. This could be useful to prevent breast cancer and to understand why some patients with benign breast disease develop cancer and others do not.

The researchers found that lobules in benign breast disease tissue have higher densities of multiple immune cell types compared to normal breast tissues. Among women with benign breast disease, a lack of B cells was associated with increased breast cancer risk. In those samples, the team found an increase in macrophages, a type of cell that helps eliminate foreign substances and initiates an immune response.

This study led scientists to encourage more investigation into the links between the development of cancer and the immune system of the breast, specifically the role of macrophages and B cells in inhibiting or promoting breast cancer.