14). This article focuses on the role of tryptophan metabolites generated by the KP in tumour growth. The technique known as single-cell RNA sequencing, or scRNA-seq, is used to highlight the diversity of intricate biological systems. Ashley et al. collected samples before Tyrosine kinase inhibitors targeted therapy and residual lesions during progressive disease (PD) for single-cell sequencing analysis, revealing upregulation of KP metabolic pathway enzyme gene expression during PD (Ref. 15). Here, NPPA is linked to neoplasm.