Exon 21 missense mutations seen in triple negative breast cancers. (A, B) Diagrams show substitution of T to G at mRNA coding nucleotide sequence 2573; leucine to arginine amino acid change at codon 858 (L858R). (C, D) Substitution of C to T at mRNA coding nucleotide sequence 2540, resulting in a threonine to isoleucin substitution at amino acid codon position 847. Tracings in both (A, C) sense and (B, D) antisense directions. The wild type sequence is shown in capital letters, while the missense nucleotide is highlighted in red lowercase letters.