Case Report: Histopathological Diagnosis of Canine Sweat Gland Adenocarcinoma

Introduction Sweat gland adenocarcinoma, also known as apocrine sweat gland carcinoma, is a rare malignant tumor in dogs, typically affecting older animals. These tumors often appear as cutaneous or subcutaneous masses on the head, neck, limbs, or thorax, presenting as firm, reddish-purple nodules that may ulcerate. The lesions can mimic other skin tumors, such as basal cell carcinoma or sebaceous gland adenocarcinoma, making histopathological evaluation essential for diagnosis. Characterized by varied growth patterns, including nodular, solid, or tubular forms, these tumors show malignant features like cellular atypia and mitotic activity. This case report describes the histopathological diagnosis of a sweat gland adenocarcinoma in a dog, highlighting the importance of microscopy in confirming this uncommon neoplasm. Case Presentation A ۹-year-old male mixed-breed dog was presented to a veterinary clinic with a solitary cutaneous mass on the left forelimb, noticed by the owner four months earlier. The mass had grown progressively, reaching ۴.۵ × ۳.۰ cm at examination. It appeared as a firm, raised, partially ulcerated nodule with a reddish-purple surface. No systemic signs, such as weight loss or lethargy, were reported, and physical examination showed no regional lymph node enlargement or signs of metastasis. Diagnostic Evaluation A surgical biopsy was performed under local anesthesia, and the tissue was fixed in ۱۰% neutral buffered formalin, processed routinely, and stained with hematoxylin and eosin (H&E). The tumor primarily consisted of large epithelioid cells with atypical, vesicular nuclei and abundant eosinophilic cytoplasm, interspersed with smaller cells showing darker, angulated nuclei. Notable stromal changes, including fibrosis and hyperemia, were present, along with frequent mitotic figures (۳-۵ per high-power field), cellular pleomorphism, and spindling of tumor cells, indicating malignancy. These features were consistent with apocrine sweat gland adenocarcinoma. Discussion Sweat gland adenocarcinomas are uncommon in dogs, with few studies detailing their characteristics. A study by Kycko et al. (۲۰۱۶) reported that these tumors primarily affect dogs aged ۸-۱۴ years, with mixed-breed dogs and German Shepherds being common. This case, involving a ۹-year-old mixed-breed dog, aligns with those findings. The observed histological features-nodular, solid, and tubular growth patterns, cellular pleomorphism, and mitotic activity-match descriptions in the literature. The mix of growth patterns is a key feature of ASGCs, distinguishing them from more uniform tumors like sebaceous adenocarcinomas. While treatment was not pursued here, literature suggests wide surgical excision offers a good prognosis if metastasis is absent. Metastasis, seen in up to ۳۰% of cases, often involves lymph nodes or lungs, worsening outcomes. No metastasis was evident in this case. Conclusion This case report details the histopathological diagnosis of a sweat gland adenocarcinoma in a ۹-year-old mixed-breed dog, emphasizing its hallmark features: multiple growth patterns, cellular pleomorphism, and mitotic activity. The findings align with open-access literature, highlighting histopathology's role in diagnosing this rare tumor. Veterinary clinicians should consider ASGC for cutaneous masses in older dogs, especially those with atypical or ulcerated lesions.

Keywords:

Sweat gland adenocarcinoma , Apocrine carcinoma , Canine tumor , Histopathology