L858R EGFR mutant expressions in triple negative, luminaland HER2 breast cancer
The presence of EGFR mutation L858R conferring sensitivity to Tyrosine Kinase Inhibitor (TKI) in primary breast cancer has been unclear. An anti L858R EGFR mutant protein specific antibody was used to screen EGFR mutations in 174 Formalin Fixed Paraffin Embedded (FFPE) specimens. Immunohistochemistry revealed strong reactions to the L858R antibody in 16 out of 174 specimens. The proportion of positive staining was highest in HER2 (11 of 16), followed by the triple negative (2 of 55) and luminal (3 of 103) subtypes. However, upon DNA isolation and analyses, there were six L858R mutations, four L861Q mutations, and the remaining six had no mutations. HER2 had the highest proportion of confirmed EGFR L858R and L861Q mutations (31%; n = 16), followed by the triple negative (3.6%; n = 55), and Luminal (1.9%; n = 103) cancer subtypes. While EGFR mutation was rare, HER2 subtype had the highest frequency of TKI sensitising EGFR mutations.