+ Biologic Behavior

• 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)

+ Diagnosis

FNA although difficult to differentiate benign from malignant

+ Treatment

• 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

+ Prognosis

• Excellent
• Recurrence rate < 10% following castration and surgical resection

+ Biologic Behavior

• 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 features

• 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

+ Diagnosis

• 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

+ Treatment

Surgery

• 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

+ Prognosis

• Excellent
• Recurrence rate < 10% following castration and surgical resection

+ Surgery

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

+ Chemotherapy

• Indications: inoperable or metastatic perianal ADC
• Doxorubicin ± cyclophosphamide is associated with short-term PR

+ Prognosis

• 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