Adenoid cystic carcinoma (ACC) is a major histological type of salivary gland cancer but an uncommon form of vulvar cancer. Salivary gland ACC occasionally dedifferentiates into high-grade carcinoma, resulting in poor prognoses. The dedifferentiated component is usually a poorly differentiated cribriform or solid carcinoma, whereas squamous cell carcinoma (SCC) is exceptional. Herein, we report the case of a 78-year-old woman with vulvar ACC, including an SCC component. She presented with a vulvar nodule that had been present for 30 years and increased in size over the past few years. Magnetic resonance imaging showed a ball-like mass with high intensity on T1-weighted images and high intensity with non-uniformity on T2-weighted images. Considering the systemic and social conditions, the tumor was maximally resected without lymphadenectomy. Histologically, the tumor was composed of a marginal ACC component with a central SCC component. Stage IB vulvar cancer, which was assumed to originate from the Bartholin's gland, was diagnosed. She has survived over 2 years without additional treatments after the surgery. In this case, we assumed that slowly progressive indolent ACC could be dedifferentiated to high- grade SCC. According to our review of available literature, dedifferentiation of vulvar ACC with a high-grade SCC component has not been specifically documented. Although the nature of dedifferentiated vulvar cancer is unclear, it should be noted that high-grade dedifferentiation can occur in long-lasting vulvar masses.
Keywords: adenoid cystic carcinoma; dedifferentiation; prognosis; squamous cell carcinoma; vulvar cancer.