Although messenger RNA translation is tightly regulated to preserve protein synthesis and cellular homeostasis, chronic exposure to interferon‐γ (IFN‐γ) in several cancers can lead to tryptophan (Trp) shortage via the indoleamine‐2,3‐dioxygenase (IDO)‐ kynurenine pathway and therefore promotes the production of aberrant peptides by ribosomal frameshifting and tryptophan‐to‐phenylalanine (W>F) codon reassignment events (substitutants) specifically at Trp codons. Here, IDO1 is linked to cancer.