To validate whether IDO1 expression is associated to BCG response in a validation cohort of T1 HR patients, follow up data and BC samples have been retrieved from a retrospective cohort of n = 28 responder and n = 47 non-responder BC patients who received six weekly instillations of BCG as induction therapy and successively maintenance therapy at P. Giaccone University hospital (Table 1). This evidence concerns the gene IDO1 and breast cancer.