Background: Primary invasive ductal carcinoma of the vulva, also known as adenocarcinoma of mammary gland type (AMGT), is an exceptionally rare malignancy arising from specialized anogenital mammary-like glands (AGMLGs). Diagnosing this condition poses a significant clinical challenge, as it requires rigorous differentiation from other primary vulvar tumors and, most importantly, secondary metastasis from breast cancer.
Case Presentation: A 64-year-old female presented with a firm, asymptomatic subcutaneous mass measuring approximately 1.2 cm in the left labium majus, with clinically negative inguinal lymph nodes. Comprehensive breast imaging, including mammography and ultrasonography, revealed no evidence of malignancy, effectively ruling out a primary breast tumor.
Findings: Histopathological evaluation of the resected tumor demonstrated an invasive ductal carcinoma (Grade 2) with an infiltrative growth pattern of cords and tubules, resembling breast invasive ductal carcinoma. Immunohistochemical (IHC) profiling revealed strong, diffuse nuclear positivity for GATA3, ER, and PR, alongside cytoplasmic positivity for CK7. Conversely, markers including SOX10, p63, CK5/6, and CK20 were entirely negative.
Conclusion: The IHC profile demonstrated a complete phenotypic overlap with luminal breast carcinomas, confirming the diagnosis of primary invasive ductal carcinoma of the vulva originating from MLGV. A multidisciplinary diagnostic strategy combining advanced breast imaging with up-to-date immunohistochemical panels is crucial for preventing misdiagnosis and guiding targeted clinical management.