A 3-year-old Japanese boy presented with a tumor in the anterior chest wall (Fig. 1). He had been vaccinated with bacillus Calmette-Guerin (BCG) at the age of 6 months. There was no history of tuberculosis exposure or infection in his family. On physical examination an immobile, firm mass was detected on the chest wall. Chest computed tomography and magnetic resonance imaging showed a 50 × 24 × 88 mm subcutaneous lobular cystic lesion on the precordium. Contrast enhancement was not observed in the central zone, but was visible in the capsule. Plastic surgeons resected the mass. Histopathology indicated a granulomatous infiltrate with central caseation necrosis and Langerhans-type giant cells, but no microbiological analysis was performed. Treatment was begun after resection. Gallium scintigraphy indicated no abnormal radioisotope accumulation. He was treated with isoniazid, rifampicin, and pyrazinamide for 6 months without any complications. Ziehl-Neelsen staining for acid-fast bacteria was positive. In granulomatous diseases, it is impossible to distinguish BCG infection from Mycobacterium tuberculosis infection histologically. To overcome the limitation, genetic analysis was performed for DNA purified from the formalin-fixed paraffin-embedded (FFPE) tissues after treatment. M. bovis-BCG Tokyo-172 genotypes harbor a single-nucleotide polymorphism (SNP) in codon 311 of fibronectin-binding protein A (fbpA), and this SNP may be a specific genetic marker for M. bovis-BCG Tokyo isolates.1 On polymerase chain reaction (PCR)-mediated DNA sequencing analysis we identified this same SNP, indicating that the bacillus was M. bovis, and strongly suggesting BCG infection. Immunology was normal, including nitroblue tetrazolium test, peripheral blood lymphocyte subsets, and in vitro lymphoproliferative responses to mitogens. Serological testing for HIV was non-reactive. Genetic analysis indicated no abnormality in immunodeficiency-related genes. The patient was healthy and had no complications after 1 year of follow-up.This case illustrates that BCG infection can cause tumor on the anterior chest wall in immunocompetent patients. Generally speaking, BCG is considered to be a safe vaccine.2-4 Literature search identified five previous reports of tumor caused by BCG infection in immunocompetent patients. [2][3][4][5][6] Similar to the present case, all patients developed tumors in the chest wall, but only two were confirmed to be caused by BCG on PCR analysis.2,4 Polat and Belen reported the case of a healthy 15-month-old boy with a mass on the anterolateral side of the left chest wall, 2 and Su et al. reported the case of a healthy 4-year-old girl who presented with a mass on the right anterior chest wall.4 None used FFPE tissues for PCR. Therefore, the present approach to investigate the etiologic agent, involving FFPE specimens, is different to that of the previous reports. This may not be a suitable approach in the clinical settings in terms of cost and labor, however, because PCR analysis of FFPE specimen requires additiona...