Vulval apocrine adenocarcinoma with tumour-associated eosinophilia in a cat

A 10-year-old, spayed female, Domestic Shorthaired cat was referred for surgical removal of a mass on the left vulval fold. An impression smear revealed mixed cell inflammation, with eosinophils predominating focally, and a concurrent bacterial infection, suggesting a primarily inflammatory lesion. However, cytology of a fine-needle aspirate of the mass revealed a neoplastic epithelial cell population, confirmed on histopathology as an apocrine vulval adenocarcinoma with lymphatic invasion and marked tumour-associated tissue eosinophilia. One month after surgical excision of the mass, the cat developed inguinal metastatic lymphadenopathy and chemotherapy was initiated. The patient ultimately developed marked peripheral lymphadenomegaly and was euthanized due to concerns for overall quality of life and comfort. This case highlights that neoplasia should be a consistent differential diagnosis for eosinophilic infiltrates/inflammation. The distinct appearance of the two cytological samples in this case stresses the need for sampling of different sites of a lesion and the importance of not relying on superficial impression smears for clinical management and prognosis.