Triple-Negative Breast Cancer: Clinical and Histological Correlations

SUMMARY: Triple-negative breast cancer (TNBC) is characterized by the lack of estrogen and progesterone receptors and the lack of HER2 expression or amplification. Much interest has recently been focused on these triple-negative (TN) subtypes because they may be aggressive and are more likely to recur and metastasize than other subtypes of breast cancer. TNBC accounts for approximately 10-24% of all breast cancer cases, and typically it occurs in younger patients and in patients with BRCA1 mutation. There is a substantial heterogeneity of TNBCs both at the morphological and the molecular level, but there are also common features, such as low tumor grade and accelerated tumor proliferation. Morphologically, TNBC may present as invasive ductal, metaplastic, medullary, apocrine, or other types. Molecularly, they are most frequently associated with a basal phenotype, but there is a distinct subgroup of cancers that are not of basal type and belong to the claudin-low or molecular-apocrine type. The basal phenotype is frequently associated with the loss of BRCA1.