The study aimed to investigate how Tryptophan 2,3-dioxygenase (TDO2)-associated tryptophan metabolism influences TLS maturation and B cell class switching in breast cancer.<h4>Methods</h4>Bulk transcriptomic data from The Cancer Genome Atlas-Breast Invasive Carcinoma (TCGA-BRCA, <i>n</i> = 1055) were analyzed using Gene Set Variation Analysis (GSVA)-based metabolic scoring, immune deconvolution, and TLS quantification. This evidence concerns the gene TDO2 and breast cancer.