The RUNX1
transcription factor is widely recognised for its tumour suppressor effects in leukaemia. Recently a putative link to
breast cancer has started to emerge, however the function of RUNX1 in
breast cancer is still unknown. To investigate if RUNX1 expression was important to clinical outcome in primary breast tumours a tissue microarray (TMA) containing biopsies from 483 patients with primary operable invasive ductal
breast cancer was stained by immunohistochemistry. RUNX1 was associated with
progesterone receptor (PR)-positive tumours (P<0.05), more tumour CD4+(P<0.05) and CD8+(P<0.01) T-lymphocytic infiltrate, increased tumour CD138+plasma cell (P<0.01) and more CD68+macrophage infiltrate (P<0.001). RUNX1 expression did not influence outcome of oestrogen receptor (ER)-positive or HER2-positive disease, however on univariate analysis a high
RUNX1 protein was significantly associated with poorer
cancer-specific survival in patients with ER-negative (P<0.05) and with triple negative (TN) invasive
breast cancer (P<0.05). Furthermore, multivariate Cox regression analysis of
cancer-specific survival showed a trend towards significance in ER-negative patients (P<0.1) and was significant in triple negative patients (P<0.05). Of relevance,
triple negative breast cancer currently lacks good
biomarkers and patients with this subtype do not benefit from the option of targeted
therapy unlike patients with ER-positive or HER2-positive disease. Using multivariate analysis RUNX1 was identified as an independent prognostic marker in the triple negative subgroup. Overall, our study identifies RUNX1 as a new prognostic
indicator correlating with poor prognosis specifically in the triple negative subtype of human
breast cancer.