One of the right inguinal lymph nodes was excised and corresponding formalin-fixed paraffin-embedded (FFPE) sections were used to histologically and immunohistochemically confirm that the metastatic tumor tissue originated from the pulmonary adenocarcinoma (same morphology of mucin-producing adenocarcinoma and IHC-profile with CK7+, TTF1+, CK20-, CDX2-, PSA-). The gene discussed is MUC5AC; the disease is adenocarcinoma.