Triple-negative breast cancer: epidemiological considerations and recommendations

Breast cancer is a major problem for global public health. Breast Cancer is the most common incident form of cancer in women around the world. The incidence is increasing while mortality is declining in many high-income countries. The last decade has seen a revolution in the understanding of breast cancer, with new classifications proposed that have significant prognostic value and provide guides to treatment options. Breast cancers that demonstrate the absence of oestrogen receptor and progesterone receptor and no overexpression of human epidermal growth factor receptor 2 (HER2) are referred to as triple-negative breast cancer (TNBC). There is now evidence emerging from epidemiological studies regarding important characteristics of this group of tumours that carry a relatively poorer prognosis than the major breast cancer sub-types. From this review of available data and information, there are some consistent findings that emerge. Women with TNBC experience the peak risk of recurrence within 3 years of diagnosis, and the mortality rates appear to be increased for 5 years after diagnosis. TNBC represents 10%-20% of invasive breast cancers and has been associated with African-American race, deprivation status, younger age at diagnosis, more advanced disease stage, higher grade, high mitotic indices, family history of breast cancer and BRCA1 mutations. TNBC is regularly reported to be three times more common in women of African descent and in pre-menopausal women, and carries a poorer prognosis than other forms of breast cancer. Although prospects for prevention of non-hormone-dependent breast cancer are currently poor, it is still important to understand the aetiology of such tumours. There remains a great deal of work to be done to arrive at a comprehensive picture of the aetiology of breast cancer. Key recommendations are that there is a clear and urgent need to have more epidemiological studies of the breast cancer sub-types to integrate aetiological and lifestyle factors for prevention of incidence and death, and to have more population-based information of the clinical and biological relevance from cancer registries.