A Case Report of an Intrathoracic Mass Lesion Caused by Arcanobacterium haemolyticum that Required Exclusion of a Malignant Tumor Diagnosis.

A 57-year-old man with untreated diabetes mellitus was admitted to our hospital due to an intrathoracic mass lesion infiltrating the vertebral body and mediastinum. The mass was suspected to be invasive lung cancer; however, percutaneous needle biopsy revealed that the mass was inflammatory granulation tissue caused by an Arcanobacterium haemolyticum infection. To the best of our knowledge, this is the first report of an intrathoracic mass lesion caused by an A. haemolyticum infection. When an intrathoracic mass lesion is suspected, clinicians should consider possible infections that cause granulation tissue, such as A. haemolyticum. This is particularly important in immunocompromized hosts such as patients with diabetes.