Vulvar and vaginal tumours account for 2.4-3% of neoplasms in dogs, while precise data are not available for cats. In the bitch, vaginal and vulvar tumours constitute about 40% and 34%, respectively, of genital neoplasms, which are the most frequent reproductive system tumours after mammary tumours.
SIGNALMENT AND HISTORY
In the bitch vulvo-vaginal tumours (Fig. 1) develop between the ages of 2 and 18 years, with the median age at presentation being 11 years. Although it is difficult to determine a precise predisposition in certain breeds, a higher incidence has been reported in Boxers, Poodles and German Shepherds.
Vaginal leiomyomas are observed more frequently in sexually intact (more than 65%) and elderly (mean age, 10 years) bitches, whereas lipomas tend to appear in younger animals, from 1 to 8 years old, with a mean age at presentation of about 6 years. Some studies have found that the frequency of benign vulvar or vaginal tumours is higher in small bitches while that of malignant tumours is higher in large breeds. These tumours are not associated with changes in the reproductive cycle or pseudopregnancy and any interference with fertility derives from hormonal imbalances that are a co-cause of the development of the tumour rather than a direct effect of the neoplasm itself. There are conflicting data on whether nulliparous or, contrariwise, multiparous bitches have a greater predisposition to the development of leiomyomas.
Sporadic cases of leiomyoma and fibroma have been described in the queen, with leiomyomas being found more frequently in elderly animals, whether sexually intact or spayed. The vagina is only occasionally the site of metastatic disease. Reports of vulvar tumours in this species are even rarer (Fig. 2).
BIOLOGICAL BEHAVIOUR
Most vulvo-vaginal tumours in the bitch are benign (>70-80%) and originate from vaginal smooth muscle; these tumours include leiomyoma, fibroleiomyoma, fibroma, fibrolipoma, fibropapilloma (polyp), lipoma, histocytoma, benign melanoma, myxoma, fibromyoma and sebaceous adenoma. Leiomyomas are the vulvo-vaginal tumours most frequently observed in the bitch (30-80%).
The malignant neoplasms in the bitch constitute about 20-30% of vulvo-vaginal tumours and include transmissible venereal tumour, leiomyosarcoma, squamous cell carcinoma, haemangiosarcoma, adenocarcinoma, fibrosarcoma, lipoleiomyosarcoma, mast cell tumour, anaplastic carcinoma, lymphosarcoma metastases from mammary carcinoma or osteosarcoma and local invasion of transition cell carcinomas.
Leiomyoma, the most common vaginal neoplasm in the bitch, may be single (Fig. 3) or multiple (Fig. 4), sessile or, more frequently, pedunculated (Fig. 5); they are usually well encapsulated and slow-growing and are often related to chronic stimulation by oestrogens (from ovarian tumours or cysts) or to the iatrogenic administration of oestrogens or progestins. Many leiomyomas originate from the vaginal vestibule and are poorly vascularised and well encapsulated; when sectioned, they are greyish-white or brown coloured.
A leiomyosarcoma is normally sessile, multilobulated, infiltrating (Figs. 6 and 7), with necrotic areas and develops independently of the presence of the ovaries. It metastasises to lymph nodes, the spleen, lungs and cervical spine, but in some cases may recur without producing metastases. One rare, very malignant tumour is vestibular carcinoma, which frequently metastasises and is often fatal. This is a squamous cell carcinoma, which may originate from the urinary tract, and presents as a plaque or multinodular lesion.
SIGNS AND DIAGNOSIS
Vaginal tumours in both the bitch and queen may develop inside or outside the lumen of the organ, with the predominant clinical signs, caused by the masses, depending on which occurs. The tumours may protrude from the vulvar cleft (Fig. 8) and be ulcerated or have areas of necrosis (Fig. 9), or, in the case of extraluminal growth, cause perineal swelling (Fig. 10).
The masses are frequently multiple in bitches, whereas they are single in queens. Vaginal tumours can be associated with various concomitant signs such as continuous or intermittent vulvar discharges, which may be haemorrhagic, mucoid, muco-purulent, or a mixture of blood and mucus, accompanied by licking, or strangury, dysuria, pollakiuria, haematuria or urinary incontinence, rectal compression or tenesmus, loss of appetite and weight or by disorders such as cystic-pyometric endometrial hyperplasia, cystitis or ovarian tumours.There are also reports in the queen of constipation secondary to compression of the colon.
The diagnosis is based on a clinical examination accompanied by cytology (Fig. 11) or biopsy of 
the mass or masses with the aim of distinguishing benign growths from malignant ones, thus enabling the correct diagnosis and therapeutic approach to be made; the definitive diagnosis does, however, depend on the findings of the histological examination performed after complete removal of the neoplasm. Clinical examination, colposcopy, digital vaginal palpation, retrograde colpography and urethrocystography can be used to identify and localise masses, determine how many there are and reveal their morphological characteristics (sessile or pedunculated). Radiography of the caudal part of the abdomen can be useful when tumours extend cranially or to evaluate sub-lumbar lymph nodes. X-rays may show dorsal shifting or compression of the rectum, cranio-ventral displacement of the bladder, or urinary or faecal retention. The TNM staging system includes the data collected during the clinical examination, but also information gained from supplementary investigations (chest X-ray, abdominal ultrasound, or also magnetic resonance imaging and computed tomography) and post-operative studies (histological examination) of all the masses present. For the purposes of staging vulvo-vaginal tumours, the regional lymph nodes are the superficial inguinal, sacral and internal iliac lymph nodes. The differential diagnosis includes hyperplasia and vaginal prolapse, carcinomas of the urinary tract invading the vagina and vulva, haematomas and vaginal abscesses, besides metastases from other sites.
TREATMENT
The treatment of vaginal tumours, performed after episiotomy and urethral catheterisation (Fig. 12), is complete surgical removal (Figs. 13, 14 and 15) and, in some cases, colpectomy with urethroplasty or vulvo-vaginectomy with a perineal urethrostomy. The episiotomy allows not only the real extent and site of the mass causing the signs to be determined, but also enables inspection of the vaginal cavity which often contains other growths that escape detection during the clinical examination (Fig. 16). Some authors advise concomitant ovariohysterectomy in the presence of both benign and malignant tumours, even though other researchers have not recorded recurrences in bitches with benign or malignant tumours which do not undergo concomitant ovariohysterectomy. In the case of a malignant neoplasm, the surgical asportation of the mass must be associated with appropriate chemotherapy.
PROGNOSIS
The prognosis of benign tumours is good and surgical removal of these neoplasms has been shown to be curative. If hormones are involved in the pathogenesis of benign vulvo-vaginal neoplasms, contemporary gonadectomy prevents recurrences, which are observed in 15% of bitches not gonadectomised. The prognosis is guarded or very poor in cases of squamous cell carcinoma and adenocarcinoma because of the marked tendency of these malignancies to recur and metastasise.
Transmissible venereal tumour
Transmissible venereal tumour (TVT) of the dog, also known as Sticker’s tumour, venereal granuloma, transmissible sarcoma, or transmissible venereal sarcoma, is a particular type of neoplasm that occurs throughout the world, but is more frequent in tropical and subtropical areas with a high density of stray dogs. TVT has the peculiar feature of deriving from transplanted allogeneic cells, i.e. of being a transmissible cancer. The antigenic characteristics of the malignant cells show that all TVT derive from a single, original canine tumour. The transmission typically occurs by transplantation of neoplastic cells on genital, oral or nasal mucosa during coitus or licking or smelling the genitals. Cases of transplantation on perianal skin, rectal mucosa and areas of excoriated skin have also been described.
The expression of the tumour is dependent on the immune status of the subject, with rapid growth and metastases occurring in immunodepressed dogs. Local invasion occurs in about 40% of cases; metastases, which are observed in approximately 5-15% of cases, occur in the skin, regional lymph nodes, tonsils, eyes, brain, pituitary gland, nose, tongue, lips and various abdominal and thoracic organs. TVT usually affects young, sexually mature animals aged between 1.5-11 years (average 4-5 years); there is predominance of cases in females, but no breed predisposition. The signs are perineal swelling, or one or more vaginal, vestibular or vulvar masses or a bloody serous vulvar discharge.
The presence of metastases or lesions of the oral or nasal mucosa causes the appearance of specific signs. The neoplasm initially appears as small, red or grey nodules, which grow to become pedunculated, cauliflower-shaped masses of even more than 10 cm in size. These masses are friable, bleed easily and have multiple haemorrhagic or ulcerated areas. The diagnosis is based on the clinical examination and cytological evaluation of exfoliated neoplastic cells, which is essential for the differential diagnosis. TVT is a round-cell tumour with the cells having a high nucleus/cytoplasm ratio, large nucleoli and numerous mitoses.
The treatment of TVT ranges from surgical excision to cryosurgery, radiotherapy and immunotherapy and depends on the site and size of the tumour and whether there are any metastases present. In the absence of metastases, surgical excision of small masses was long used with apparent success, but because of the high rate of recurrences (over 40%), it has now been abandoned in favour of the more effective chemotherapy which is currently the treatment of choice because of the high rate of resolution of the disease and its efficacy in controlling metastases.
Chemotherapy involves the use of vincristine or vincristine associated with cyclophosphamide and methotrexate, even if the chemotherapy combinations have not been demonstrated to be more effective than vincristine alone given intravenously in cycles of 0.7 mg/m2/7 days and continued for one or two cycles after complete remission has been achieved. A possible resistance to chemotherapy or its reduced efficacy has been reported in bitches in oestrus, despite the fact that TVT does not have α receptors for oestrogens. Spontaneous remission of the tumour has been observed following experimentally induced infections, but not after spontaneous infections.
Suggested readings
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- Klein MK (2007) Tumors of the female reproductive system. In: Withrow SJ, Vail D. Withrow and MacEwen’s small animal clinical oncology. Saunders, S.Louis: 610-618.
- McEntee MC (2002) Reproductive oncology. Clin Tech Small Anim Pract,17: 133-149.
- JohnstonSD, Root Kustritz MV, Olson PNS (2001) Disorders of the feline vagina, vestibule, and vulva. In: Canine and Feline Theriogenology. Saunders 3rd ed Philadelphia: 472-473.
- JohnstonSD, Root Kustritz MV, Olson PNS (2001) Disorders of the canine vagina, vestibule, and vulva. In: Canine and Feline Theriogenology. Saunders 3rd ed Philadelphia: 225-242.
- Morris J, Dobson JM (2001) Genital tract. In: Small animal oncology, Blackwell, Oxford: 166-174.