IDO1 and neoplasm: In POAI group, tumours transitioning from LumB or HER2-E to LumA exhibited significant molecular alterations, including upregulation of mammary stemness and various immune-related signatures such as PDL1 or PDL2, macrophages, tumour inflammation signature (TIS), TGF-beta, and IDO1. In contrast, signatures of TP53 surrogate mutational status, HRD, proliferation and genomic risk were reduced in tumours shifting from LumB or HER2-E at baseline to LumA compared to those that retained their original subtype.