JPC SYSTEMIC PATHOLOGY
Signalment (V04-14822): Tissue from a cat
HISTOPATHOLOGIC DESCRIPTION: Haired skin and bone (1st and 2nd phalanges), digit, longitudinal section: Expanding the dermis, elevating the overlying multifocally hyperplastic epidermis, and compressing the distal aspect of bone of the 2nd phalanx is an unencapsulated, poorly demarcated, moderately cellular neoplasm composed of respiratory epithelial cells arranged in islands and acini on a dense desmoplastic stroma. Neoplastic cells are columnar to cuboidal with an apical lining of cilia; distinct cell borders; a moderate amount of eosinophilic, finely granular cytoplasm; and a round to oval, basally located nucleus with finely stippled chromatin and one distinct nucleolus. There is moderate anisocytosis and anisokaryosis. Mitotic figures average 2 per 10 HPF, and there is multifocal single cells necrosis. Within the superficial dermis and surrounding and separating superficial neoplastic islands and acini is a focally extensive area of disorganized granulation tissue characterized by increased numbers of small caliber blood vessels typically oriented perpendicular to the epidermis and plump fibroblasts typically perpendicular to the vessels; granulation tissue is admixed with occasional neutrophils and separated by clear space (edema). The overlying epidermis is moderately hyperplastic with acanthosis and rete ridge formation, and exhibits multifocal spongiosis.
MORPHOLOGIC DIAGNOSIS: Haired skin and bone, digit: Metastatic pulmonary carcinoma, feline.
DISEASE: Lung-digit syndrome
· Metastasis of internal tumors to the skin is rare in cats; pulmonary carcinoma is the most commonly reported
· Other reports of cutaneous metastasis of internal tumors in cats include mammary adenocarcinoma (metastasis to the ventral abdominal tissue via direct invasion of dermal lymphatics or retrograde metastasis from lymph node) and digestive carcinoma
· Pulmonary adenocarcinomas in cats have a high propensity to metastasize to the digit possibly due to the high digital blood flow and weight-bearing function of the digit; however they can metastasize to other sites in the skin or other locations (e.g. brain, muscle, eye, bone)
· Pulmonary adenocarcinoma is relatively common in older cats, there is no breed or sex predilection
TYPICAL CLINICAL FINDINGS:
· Metastasis usually occurs prior to the onset of clinical signs from the primary neoplasm
· Lameness with minimal to absent pulmonary signs
· Radiographs of the digit reveals bony lysis of the phalanx
· Thoracic radiographs classically reveal a single, large, circumscribed mass in the caudal left lung field
TYPICAL GROSS FINDINGS:
· Lesions are suggestive of paronychia (inflammation of the skin that surrounds a nail)
· May have lesions on multiple digits, dewclaw is excluded
· Swelling, skin ulceration, purulent discharge may be present
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Nests, solid sheets, and glandular structures composed of malignant respiratory epithelial cells in the dermis and subcutis, especially the dorsum of the distal phalanx or beneath the footpad epidermis
· Neoplastic respiratory cells have abundant eosinophilic cytoplasm, basally oriented nuclei, and frequent apical cilia
· Glandular lumens may contain necrotic cellular debris
· Squamous differentiation is common
· Desmoplasia is usually present
· Mitotic activity is variable
· Bony lysis of the phalanx
· May involve multiple digits
ADDITIONAL DIAGNOSTIC TESTS:
· Histochemical stains: Neoplastic cells often contain and secrete mucin (PAS positive), whereas primary adenocarcinomas of the digit would be PAS negative
· Immunohistochemistry: Pulmonary adenocarcinomas are immunoreactive for TTF-1, whereas primary cutaneous glandular neoplasms are immunoreactive for CAM5.2 (CK7/8) and CK13
· Squamous cell carcinoma is most common digit tumor followed by fibrosarcoma
· Causes of paronychia: bacterial and fungal infection, immune mediated disease
· Primary cutaneous apocrine or eccrine carcinoma: epithelium is not ciliated; TTF-1 negative; immunoreactive for CAM5.2 (CK7/8) and CK13
· Eccrine carcinomas are rare
· Bony invasion by an apocrine adenocarcinoma is unlikely
Cutaneous metastasis of visceral neoplasia:
· Urothelial (transitional cell) carcinoma (U-N04): Cutaneous metastasis has been reported after abdominal surgery; most cases of cutaneous lesions are plaques, papules, and nodules close to the vulva or prepuce, possible that urine may seed the neoplastic cells to scalded skin
· Visceral hemangiosarcomas (C-N02) may metastasize to the subcutis; a subcutaneous location of hemangiosarcoma suggests a primary visceral tumor
· Mammary gland carcinomas: may metastasize to the dermis of the inner thigh
· Other reported cutaneous metastases: mast cell tumors, lymphoma, duodenal and colonic adenocarcinoma, gastric mucinous adenocarcinoma, inflammatory mammary carcinosarcoma, seminoma, osteosarcoma, nasal neuroendocrine carcinoma, rhabdomyosarcoma
· Llama: report of cutaneous metastasis of mammary adenocarcinoma (Mauldin, Jubb, Kennedy and Palmer’s Pathology of Domestic Animals 2016)
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