A Delayed Foreign Body Reaction to a Hemostatic Agent Mimicking Neoplasm.

Hydrophilic polymer-based hemostatic agents containing potassium ferrate are increasingly used in dermatologic surgery due to their rapid, coagulation-independent mechanism of action. While considered safe, delayed foreign body reactions to these agents are underrecognized and may mimic neoplastic recurrence, hypertrophic scarring, or cyst formation. We present the case of a 63-year-old man who developed a persistent papule at the site of a prior biopsy, clinically concerning for squamous cell carcinoma or residual cyst. Histopathologic evaluation revealed amorphous basophilic material with associated orange-red and yellow-brown granules, positive for iron on Prussian blue staining, surrounded by granulomatous and lymphohistiocytic inflammation. These findings were diagnostic of a foreign body reaction to hydrophilic polymer and potassium ferrate, likely introduced during the initial procedure. This case highlights the importance of recognizing the distinct histologic features of these reactions, especially when the procedural history is incomplete, to avoid misdiagnosis and unnecessary intervention. The prolonged latency, observed approximately one year after the initial procedure, emphasizes the need for continued vigilance by dermatopathologists and clinicians. As the use of topical hemostatic agents becomes more widespread, awareness of their potential for delayed foreign body reactions is essential for accurate diagnosis and appropriate management.