A case of activating EGFR mutation (E746_A750del) was identified in the biopsy of a young woman's sacrum (without radiologic evidence of lung or other primary cancer and equivocal IHC profile, which included diverse possible primary sites such as upper GI tract, pancreas and biliary tree, as well as triple-negative breast cancer). The gene discussed is EGFR; the disease is triple-negative breast carcinoma.