Neha Seth

Metastatic Vulvar Paget's Disease Presenting in a Supraclavicular Lymph Node: A Diagnostic Challenge on Fine Needle Aspiration Cytology

ABSTRACT Background Extramammary Paget's disease (EMPD) of the vulva is a rare intraepithelial adenocarcinoma with a typically indolent course. Distant metastasis, particularly to supradiaphragmatic lymph nodes, is exceedingly uncommon and poses a significant diagnostic challenge. Case Presentation We report a rare case of metastatic vulvar EMPD presenting as a left supraclavicular lymph node enlargement in a 72‐year‐old woman with a known history of EMPD since 2014. Cytologic smears from the lymph node revealed large, discohesive epithelial cells with pale vacuolated cytoplasm and prominent nucleoli. The concurrent core biopsy demonstrated effacement of nodal architecture by similar cells forming loose clusters and abortive glandular structures. Immunohistochemistry showed tumor cells positive for CK7, CK20, GATA3, and TRPS‐1, with focal mammaglobin expression and negative staining for CDX2, PAX8, CK5/6, P40, and P63. Special stain with mucicarmine highlighted abundant intracytoplasmic mucin—a key morphologic clue favoring EMPD over a breast primary. Conclusion This case illustrates the diagnostic complexity of EMPD metastasizing to an unusual site and highlights the critical role of cytomorphology, special stains, and immunohistochemistry in excluding alternate primaries. Mucicarmine staining highlighted abundant intracytoplasmic mucin, serving as a useful adjunct in raising suspicion for EMPD. While not specific, in conjunction with cytomorphology and immunohistochemistry, this supported EMPD over invasive ductal carcinoma of the breast. Given the rarity of such distant nodal metastases, a high index of suspicion should be maintained for EMPD in patients with a known history, even when metastases appear in non‐regional lymph nodes.