In ER-negative tumours [ triple-negative breast cancer and human epidermal growth factor receptor 2 ( human epidermal growth factor receptor 2 ( HER2 ) positive ) ] , presence of CD8 + T cells within the tumour was associated with a 28 % [ 95 % confidence interval ( CI ) 16 % to 38 % ] reduction in the hazard of breast cancer-specific mortality , and CD8 + T cells within the stroma with a 21 % ( 95 % CI 7 % to 33 % ) reduction in hazard .