Feline Lower-Lip Apocrine Sweat Gland Adenocarcinoma with Mandibular Nodal Metastasis: A Case Report.

Apocrine sweat gland adenocarcinoma is an uncommon feline adnexal neoplasm, and lower-lip involvement is rarely documented. A 14-year-old spayed female Siamese cat was evaluated for a firm 1.3 cm right lower-lip mass at a documented hemorrhagic lesion site. Approximately 1 year earlier, the lesion was fluctuant and superficially erosive to ulcerative; fine-needle aspiration yielded bloody fluid with cytologically nondiagnostic material. The lesion reportedly subsided after empirical treatment, but reassessment, tissue diagnosis, and objective confirmation of resolution were not performed. Cytology of the later same-site mass supported malignant epithelial neoplasia. Contrast-enhanced computed tomography (CT) identified a 12.5 × 13.2 × 16.6 mm rim-enhancing mass without mandibular invasion or distant metastasis; the ipsilateral mandibular lymph node was mildly thickened. Histopathology supported a diagnosis of lower-lip apocrine sweat gland adenocarcinoma with lymphovascular tumor emboli, lymphatic invasion, and nodal metastasis. The diagnosis was supported by superficial dermal/subcutaneous location, adjacent adnexal structures, skeletal-muscle separation from nearby minor salivary glands, epithelial immunoreactivity, periodic acid-chiff (PAS) and Alcian blue findings without distinct intratumoral mucin/mucopolysaccharide-rich material. The cat died without necropsy on postoperative day 87. This case supports tissue-based diagnosis and regional lymph node assessment for suspicious feline lower-lip glandular epithelial lesions.