RESUMEN
Mycobacterium bovis bacille Calmette-Guérin (BCG) is the most effective intravesical immunotherapy for non-muscle invasive bladder cancer (NMIBC), administered after its transurethral resection. Although its instillation is generally well tolerated, BCG-related infectious complications may occur in up to 5% of patients. Clinical manifestations may arise in conjunction with initial BCG instillation or develop months or years after the last BCG instillation. The range of presentations and potential severity pose an imminent challenge for clinicians. We present a case of an isolated subcutaneous chest wall abscess in an immunocompetent 52-year-old patient nearly two years after intravesical BCG instillation for NMIBC, an absolute rarity. As the enlarging chest wall tumor may be misinterpreted as malignancy, its expedient diagnosis and prompt treatment are of critical importance.