Occult breast cancer (OBC) is an asymptomatic condition. We report a case of OBC in a 72-year-old male patient who presented with severe dyspnea and upper extremity swelling. Computed tomography scan showed multiple lymph node enlargements in the supraclavicular and infraclavicular areas, and ultrasound scan showed multiple axillary lymph node enlargements. Based on the radiological findings, clinicians suspected lymphoma or disseminated metastasis from unknown primary malignancies. However, the axillary biopsy specimen revealed invasive breast cancer with hormonal receptor positivity.