Signet ring cell sinus histiocytosis. A previously unrecognized histologic condition mimicking metastatic adenocarcinoma in lymph nodes.

The axillary lymph nodes in a radical mastectomy specimen from a 70-year-old insulin-dependent diabetic patient contained significantly vacuolated sinus histiocytes. The histologic picture closely resembled metastatic signet ring cell adenocarcinoma. The signet ring histiocytes did not stain with the mucicarmine or periodic acid-schiff stains or any of the immunohistochemical epithelial markers. The differential diagnosis and the possible origin of these vacuolated histiocytes are discussed.