Triple negative breast cancer (TNBC) is a type of breast cancer (BC) that does 
not express the oestrogen and the progesterone receptors and the human epidermal 
growth factor receptor type 2 (HER2). Since there are no positive markers to 
reliably classify TNBC, these tumours are not yet treated with targeted 
therapies. Perhaps for this reason they are the most aggressive form of breast 
carcinomas. However, the clinical observation that these patients do not carry a 
uniformly dismal prognosis, coupled with data coming from pathology and 
epidemiology, suggests that this negative definition is not capturing a single 
clinical entity, but several. We critically evaluate this evidence in this 
paper, reviewing clinical and epidemiological data and new studies that aim to 
subclassify TNBC. Moreover, evidence on the role of tumour infiltrating 
lymphocytes (TILs) on TNBC progression, response to chemotherapy and patient 
outcome have been published. The heterogeneity, observed even at TILs level, 
highlights the idea that TNBC is much more than a single disease with a unique 
treatment. The exploration of the immune environment present at the tumour site 
could indeed help in answering the question 'How many diseases is TNBC' and will 
help to define prognosis and eventually develop new therapies, by stimulating 
the immune effector cells or by inhibiting immunological repressor molecules. In 
this review, we focus on the prospect of the patient's diverse immune signatures 
within the tumour as potential biomarkers and how they could be modulated to 
fight the disease.