Subclinical mastitis during lactation: a modifiable risk factor for breast cancer?

Chronic inflammation likely contributes to breast cancer risk, but epidemiologic studies are inconclusive. Two types of inflammatory episodes in breast tissue, referred to here as clinical mastitis and subclinical mastitis, have received little to no attention as risk factors for breast cancer. Clinical mastitis represents an acute painful inflammatory state of the breast that in most cases will be quickly treated and resolved. In contrast, subclinical mastitis remains undetected in most cases and may represent chronic inflammation. Based on the concentration of sodium (Na) and cytokines in milk, several publications suggest that subclinical mastitis is relatively common and can persist for extended periods. We propose that subclinical mastitis is a modifiable risk factor for breast cancer. This chronic subclinical inflammatory profile in breast tissue may cause genetic instability and perturb epigenetic mechanisms leading to cancer. We suggest studies to determine the extent that subclinical mastitis is associated with breast cancer risk.