Epidemiology of triple negative breast cancers.

Triple negative (TN) breast cancers fail to express the three most common breast cancer receptors; i.e., estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). Accumulating data demonstrate that epidemiological risk factor profiles also vary between TN (ER-PR-HER2-) and other breast cancers, especially the so-called Luminal A breast cancers (ER+PR ± HER2-) [1]. A more comprehensive understanding of the epidemiology of TN breast cancers has important public health implications for risk assessment [2], prevention and treatment. The epidemiology of TN breast cancers can be first understood in the age-related reproductive risk factor patterns for ER, PR, and HER2. For example, there is a clear and strong association between older age at diagnosis (and therefore postmenopausal status) and the development of ER positive, PR positive, and HER2 negative breast cancers. On the other hand, younger age at diagnosis (and premenopausal status) is related to the development of ER negative, PR negative, and HER2 positive breast cancers. This gives rise to the somewhat counterintuitive suggestion that menopause has a greater relative impact upon hormone receptor negative than positive breast cancers [3,4]. Throughout this review, we will primarily contrast ER-PR-HER2- (TN) with ER+PR ± HER2- (Luminal A) breast cancers. We will first summarize the population-based age-specific incidence rate patterns and clinical outcomes, and then will review the available analytical studies. Information sources for this review included the National Cancer Institute's Surveillance, Epidemiology, and End Results 13 Registries Public-Use Database [5], CANCERLIT, Index Medicus, and PubMed.