Veterinary Society of
Surgical Oncology

PERIANAL ADENOMA

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)

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

PERIANAL ADENOCARCINOMA

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

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

  • 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

PERIANAL TUMORS

Back to top