Biologic Behaviour

•common tumor arising from sebaceous glands and accounts for 80% of perianal tumors

•synonyms: circumanal adenoma and hepatoid adenoma

•very rare in cats as cats do not have perianal sebaceous glands

•androgen stimulation as increased risk in intact males and association with testicular interstitial tumors

•perianal adenoma occurs predominantly in spayed females as low estrogen levels do not suppress tumor growth

•perianal adenoma can be associated with either hyperadrenocorticism or adrenal tumor producing testosterone

Clinical Features

•breed predisposition: Cocker Spaniel, Beagle, Bulldog, and Samoyed

•sex predisposition: intact male

•slow-growing, non-painful, and usually asymptomatic mass

•single, multiple, or diffuse (similar to generalized hyperplasia or hypertrophy of perianal tissue) in males

•single and small in females

•site: superficial hairless perineum commonly involved, but other sites include the prepuce, scrotum, and tail-head

•ulceration and infection occasionally observed but rarely adherent or fixed to deeper structures

•intermediate condition called invasive perianal adenoma (histologically benign but invasive behaviour)


•FNA although difficult to differentiate benign from malignant


•castration either combined with local resection if focal or alone if diffuse, large or close to the anal sphincter

•tumor size may decrease over several months permitting easier and safer tumor resection following castration

•other treatment options include:

•radiation therapy with 69% 12-month DFI

•cryosurgery for lesions < 1-2 cm in diameter

•estrogens to cause tumor regression but bone marrow suppression a significant risk



•recurrence rate < 10% following castration and surgical resection


Biologic Behaviour

•perianal ADC is an uncommon tumor primarily arising from sebaceous glands and rarely from apocrine glands

•sex predisposition: male

•perianal ADC can occur in either intact or late-castrated males suggesting no androgen influence

•malignant lesion should be suspected if new perianal mass in castrated male or recurrent mass following castration

•perianal ADC is rarely associated with paraneoplastic hypercalcemia

•metastatic sites: regional lymph node (sublumbar) and lungs with metastasis to the regional lymph nodes in 15% dogs at diagnosis and more common in dogs with large and invasive tumors

•concurrent testicular neoplasia is common in intact dogs

Clinical Signs

•breed predisposition: German Shepherd Dogs and Arctic Circle breeds

•gross appearance: single, locally invasive and frequently ulcerated

•similar appearance to perianal adenoma

•clinical signs: presence of mass, ulceration of mass, tenesmus, and perirectal pain and irritation

•obstipation and dyschezia can occur with larger masses


•rectal examination to assess sublumbar node size and mobility

•FNA will rarely differentiate benign from malignant perianal tumors but may differentiate perianal tumors from other tumor types

•caudal abdominal radiographs or ultrasound to assess sublumbar node size ± ultrasound-guided aspirate



•wide local resection:

•resection of < 50% of anal sphincter will cause transient but not permanent fecal incontinence

•complete resection is often difficult due to proximity to rectum and poor definition of perianal area

•recurrent disease is difficult to resect

•exploratory celiotomy and sublumbar lymphadenectomy:

•sublumbar nodes can be resected in approximately 50% dogs

•resectability cannot be determined preoperatively and large sublumbar nodes do not preclude resection

•lymph node can either be invasive or easily removed

•castration minimal benefit

Radiation Therapy

•indications: inoperable or recurrent perianal ADC and metastatic inoperable sublumbar lymph node

•radiation therapy can be used either alone, intraoperatively (10-15 Gy), or as an adjuvant following surgery


•indications: inoperable or metastatic perianal ADC

•doxorubicin ± cyclophosphamide is associated with short-term PR


•fair to good

•local tumor recurrence is common and multiple palliative resections over several years may be required

•clinical stage prognostic: T0-2 N0 M0 (i.e., local tumor < 5 cm in diameter with no regional or distant metastasis)

•1-year DFI 75%

•2-year DFI 60%

•2-year survival rate > 70% survival rate

•11-times greater risk of tumor-related death if tumor > 5 cm in diameter

•45-times greater risk of tumor-related death if regional or distant metastasis







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