Cystic Squamous Cell Carcinoma with Subepidermal Cyst in a Young Dog - A Case Report

Background Squamous cell carcinoma (SCC) is a prevalent malignant neoplasm in dogs, originating from squamous epithelial cells and accounting for approximately ۵% of cutaneous tumors and the second most common oral malignancy. (۱,۲) In both canine and feline patients, squamous cell carcinoma (SCC) commonly affects the skin, oral cavity, or nail beds. For cutaneous forms, the metastatic rate is approximately ۲۰% when detected early, though this can vary significantly between species and tumor location. (۳,۴) Risk factors for SCC development include chronic ultraviolet (UV) exposure, which is particularly relevant for light-skinned or sparsely haired breeds. Less common risk factors include canine papillomavirus and chronic inflammation. (۵,۶) SCC predominantly occurs in older dogs, presenting as ulcerated, proliferative, or wart-like cutaneous lesions. (۱,۷) This case report describes an unusual cutaneous SCC with a subepidermal cyst in a young dog, highlighting its histopathological characteristics and diagnostic implications. Case Presentation A ۳-year-old male dog of unknown breed presented to a veterinary clinic with a ۱.۵ cm fluctuant cutaneous mass on the dorsal flank, observed by the owner for approximately ۲ months. The mass was non-ulcerated, and freely movable, with no pain elicited on palpation. No systemic signs, such as weight loss, lethargy, or inappetence, were reported, and the dog's general health appeared unremarkable. The owner noted occasional sun exposure due to outdoor activities, but no history of trauma, infections, or prior cutaneous lesions was reported. Physical examination revealed no peripheral lymphadenopathy, and vital parameters, including heart rate, respiratory rate, and temperature, were within normal limits. (۱۰) Diagnosis An excisional biopsy was subsequently performed for histopathological analysis. The biopsy confirmed a diagnosis of invasive SCC, revealing a subepidermal cyst lined by stratified squamous epithelium adjacent to the neoplastic component. The tumor exhibited marked polymorphism, with cells displaying irregular shapes, nuclear atypia, and numerous mitotic figures. These features, along with the infiltration of malignant squamous cell nests into the surrounding dermis, confirmed a malignant process and Subepidermal cyst, Cyst lining composed of stratified squamous epithelium with a granular layer. Discussion This case represents a rare presentation of cutaneous SCC with a subepidermal cystic component in a ۳-year-old dog, deviating from the typical demographic of older dogs (۶-۱۱ years) and clinical profile of ulcerated or solid masses. (۱,۷) The young age suggests possible unique etiological factors or genetic predispositions, though these could not be assessed due to the unknown breed. (۵) This case emphasizes the need to consider SCC in young dogs with fluctuant cutaneous masses, especially in sun-exposed areas, as UV exposure may have contributed despite the dog's age. (۵) Future research should investigate the prevalence, histopathological variants, and molecular drivers of cystic SCC in dogs to enhance diagnostic algorithms and therapeutic approaches. Clinicians are urged to include cystic SCC in differential diagnoses for fluctuant masses and prioritize histopathological evaluation to guide clinical decision-making. (۹,۱۱)

Keywords:

Squamous Cell Carcinoma , SCC , Histopathology , Subepidermal Cyst , Case Report