Clinical Significance of Propionibacterium acnes in the Formation of Noncaseating Epithelioid-Cell Granulomas of the Mediastinal Lymph Nodes and Lung in Patients with Lung Cancer:Differential Diagnosis Between Sarcoid Reactions and Sarcoidosis

Objectives:Sarcoidosis is a systemic noncaseating epithelioid-cell granulomatous disease of unknown origin.Granulomas occurring around malignant tumors and regional lymph nodes can be caused by sarcoid reactions.The mechanisms underlying sarcoidosis and sarcoid reactions remain unclear. Whether increaseduptake of fluorodeoxyglucose( FDG) in lymph nodes on positron emission tomography( PET) is caused bytumor metastasis, the concurrent presence of sarcoidosis, or sarcoid reactions must be determined to ensureproper disease staging and selection of treatment policy. We studied patients who underwent surgery forlung cancer and had no histopathological evidence of lymph-node metastasis in whom concurrent sarcoidosisor sarcoid reactions were diagnosed.Methods:In six patients who underwent surgery for primary lung cancer, granulomatous lesions werehistopathologically studied in dissected lymph nodes and lung. Tissue sections were stained with monoclonalantibodies against Propionibacterium acnes( PAB antibodies).Results:The six patients had noncaseating epithelioid-cell granulomas in mediastinal lymph nodes andlung. Clinically, concurrent sarcoidosis was suspected, but the results of staining the tissue specimens withPAB antibodies( in granulomas, alveolar macrophages, Hamazaki-Wesenberg bodies, and lymphatic sinuses)suggested sarcoid reactions in 5 patients. In one patient in whom granulomas stained positive with PAB antibodies,concurrent sarcoidosis was diagnosed.Conclusions:In patients with lung cancer who have no distinct systemic evidence of sarcoidosis, thepresence of noncaseating epithelioid-cell granulomas in the lung hilum or mediastinum is usually caused bysarcoid reactions.