Rapidly progressing Kaposi sarcoma in a human immunodeficiency virus-negative patient

Kaposi sarcoma (KS) is a vascular tumor caused by human herpesvirus-8 (HHV-8), most often associated with human immunodeficiency virus (HIV)-positive individuals. However, KS can also occur in HIV-negative patients, though less commonly. We report a rare case of classic KS in an HIV-negative man with no history of male-to-male sexual activity, who experienced rapid progression to stage IV disease within 3 months. To our knowledge, this is the first documented case of classic KS in Vietnam, highlighting the potential for aggressive KS presentations in immunocompetent Asian individuals. This case underscores the importance of considering KS in the differential diagnosis of rapidly advancing skin lesions, even in patients without traditional risk factors, to ensure timely diagnosis and appropriate management.