The patient was a 73-year-old female whose chief complaint was fatigue. Thoracic computed tomography (CT) revealed nodular shadows in both lungs and consolidation predominantly in the lower lobes. We performed a transbronchial lung biopsy and made a diagnosis of invasive mucinous adenocarcinoma. Initially, primary lung cancer was suspected, but positron emission tomography-CT showed abnormal accumulation in the pancreatic body as well, and we performed endoscopic ultrasound-guided fine needle aspiration and made a diagnosis of adenocarcinoma. Because the immunostaining findings in the pulmonary and pancreatic tissue matched (CK7-positive, CK20-, TTF-1-, SP-A-negative), and the DU-PAN-2 and SPan-1 values were high, we made a diagnosis of pancreatic cancer with pulmonary metastasis. Tumor markers and immunostaining, especially the CK7/CK20 phenotype, were useful in helping to make the differential diagnosis between invasive mucinous adenocarcinoma and pancreatic cancer with pulmonary metastasis.