Multiple Primary Lung Tumors of Different Pathological Types Including Squamous Cell Carcinoma, Adenocarcinoma, and Mixed Squamous Cell and Glandular Papilloma: A Case Report

Multiple primary lung cancer (MPLC) is considered relatively rare. This report presents an unusual case of multiple pulmonary nodules in a 74-year-old man who presented with three independent synchronous tumors in the right upper lobe. The tumors were diagnosed as peripheral squamous cell carcinoma (SCC), adenocarcinoma, and pulmonary mixed squamous cell and glandular papilloma (mixed papilloma). Mixed papilloma is an extremely rare, benign pulmonary tumor with a typical papillary appearance, showing squamous and glandular epithelial differentiation. The histological and immunohistochemical features of each tumor were analyzed. In addition, molecular pathological examination for epidermal growth factor receptor (EGFR) showed no mutation in two primary cancers. Mixed papilloma showed no BRAF V600E mutation or HPV infection. The present case report provides a clinicopathological understanding of an instance in which three tumors of different pathological types are present in the same lung lobe. Furthermore, it provides a literature review regarding multiple lung nodules, focusing on the clinicopathological diagnosis, clinical treatment, and prognostic assessment of these nodules. This is the first case report of mixed papilloma arising in MPLC.