Pathological Study of Genital and Extra Genital Transmissible Venereal Tumor (TVT) in Dogs
Sitaram Yadav(a), Dr Sarjana Meena(b), Ravi Jangid(c), Rati jalutharia(b)
(a) M.V.Sc Scholar in Veterinary Surgery And Radiology at PGIVER,Jaipur
(b)Assistant Professor in Veterinary Pathology at PGIVER,Jaipur
(c) M.V.Sc Scholar in Veterinary Surgery And Radiology at PGIVER, jaipur
(d) M.V.Sc Scholar in Veterinary Surgery And Radiology at PGIVER, jaipur
Rajasthan University of Veterinary and Animal Sciences, JOBNER, JAIPUR (Rajasthan)
Corresponding author: sita303702@gmail.com, ratijalutharia1998@gmail.com
Abstract
Canine Transmissible Venereal Tumor (TVT) is a unique naturally occurring neoplasm that is transmitted between dogs through the direct transfer of viable tumor cells. Unlike conventional cancers, which arise from mutations within an individual, TVT behaves as a clonal allograft capable of surviving and proliferating in genetically unrelated hosts. The disease primarily affects the external genital organs of male and female dogs; however, extra-genital manifestations are increasingly reported due to alternative routes of tumor cell implantation. Pathological evaluation of both genital and extra-genital TVT is essential for accurate diagnosis, understanding tumor biology, and guiding effective treatment. This article presents a comprehensive pathological overview of genital and extra-genital TVT in dogs, focusing on etiology, transmission, gross and microscopic pathology, diagnostic study methods, and overall significance in veterinary practice.
Causes and Transmission Etiology of TVT
Transmissible Venereal Tumor is caused by viable neoplastic cells rather than infectious agents such as bacteria, viruses, or parasites. These tumor cells represent an ancient clonal lineage that originated thousands of years ago and has evolved the ability to evade host immune defenses. Cytogenetically, TVT cells exhibit a stable but abnormal karyotype that is distinct from normal canine somatic cells, confirming their independent clonal nature.
The tumor behaves as a naturally occurring transplant, or allograft, capable of surviving across genetically diverse canine populations. Temporary immune tolerance, reduced major histocompatibility complex (MHC) expression, and local immunosuppression at the tumor site contribute to successful tumor establishment.
Modes of Transmission
Genital Transmission
The primary route of transmission is sexual contact during coitus. During mating, tumor cells are mechanically exfoliated from affected genital surfaces and implanted onto the genital mucosa of the partner. This explains the high prevalence of genital TVT in:
- Sexually active dogs
- Free-roaming and stray populations
- Dogs lacking reproductive control
Genital TVT commonly affects:
- Penis and prepuce in males
- Vulva and vagina in females
Extra-Genital Transmission
Extra-genital TVT occurs when tumor cells are implanted at non-genital sites. This usually results from licking, biting, sniffing, or close physical contact, especially when mucosal surfaces or skin are traumatized. The most commonly reported extra-genital sites include:
- Nasal cavity (leading to epistaxis and nasal discharge)
- Oral cavity (causing dysphagia or oral masses)
- Skin and subcutaneous tissues
- Eyes and conjunctiva
- Rectum and anus
In rare cases, metastasis to internal organs or regional lymph nodes may occur, particularly in immunocompromised dogs.
Study Method (Pathological Evaluation of TVT)
Pathological study of TVT involves a systematic approach that includes clinical evaluation, gross pathology, cytology, histopathology, and supportive laboratory techniques. These methods are essential for definitive diagnosis and differentiation from other canine round cell tumors.
Clinical and Gross Examination
Genital TVT
Grossly, genital TVT presents as:
- Friable, nodular, papillary, or cauliflower-like masses
- Pink to reddish in color
- Highly vascular and prone to ulceration
- Easily bleeding on manipulation
Affected dogs often show:
- Serosanguinous or hemorrhagic genital discharge
- Foul odor
- Excessive licking of genital region
- Difficulty in mating or urination
Extra-Genital TVT
Gross appearance varies depending on the anatomical location. Extra-genital lesions may present as:
- Nodular or ulcerated masses
- Localized swelling
- Bleeding or discharge from affected sites
For example:
- Nasal TVT causes epistaxis and facial deformity
- Oral TVT results in oral masses and difficulty eating
- Cutaneous TVT appears as firm nodules on the skin
Cytological Study
Cytology is considered the gold standard for rapid diagnosis of TVT due to its simplicity, speed, and high diagnostic accuracy.
Sample Collection
Samples can be obtained by:
- Fine needle aspiration cytology (FNAC)
- Impression smears
- Swab technique from ulcerated surfaces
Cytological Features
Characteristic cytological findings include:
- Round to oval neoplastic cells
- Large centrally placed nucleus
- Coarse chromatin with prominent nucleoli
- Moderate amount of pale cytoplasm
- Distinct intracytoplasmic vacuoles, which are a diagnostic hallmark
- High mitotic index
These features help differentiate TVT from other round cell tumors such as lymphoma, mast cell tumor, histiocytoma, and plasmacytoma.
Histopathological Study
Histopathology provides confirmatory diagnosis and deeper insight into tumor architecture and biological behavior.
Histological Features
Microscopically, TVT is characterized by:
- Sheets or cords of uniform round cells
- Scant fibrovascular stroma
- Cells resembling lymphocytes or plasma cells
- Frequent mitotic figures
- Variable inflammatory cell infiltration
In extra-genital TVT, histopathology may reveal:
- Local tissue invasion
- Ulceration and necrosis
- Secondary inflammatory changes
Although metastasis is uncommon, involvement of lymph nodes or visceral organs may be observed in advanced or untreated cases.
Ancillary Diagnostic Techniques
Additional methods used in advanced pathological studies include:
- Immunohistochemistry (e.g., vimentin positivity)
- Cytogenetic analysis
- Molecular studies to confirm clonal origin
These techniques are particularly useful in atypical cases or research settings.
Conclusion
Canine Transmissible Venereal Tumor represents a biologically extraordinary neoplasm that challenges traditional concepts of cancer development and transmission. Both genital and extra-genital forms of TVT exhibit distinctive pathological features that facilitate diagnosis when appropriate study methods are applied. Cytology remains the most practical and reliable diagnostic tool, while histopathology provides essential confirmatory and prognostic information. Awareness of extra-genital manifestations is critical for early diagnosis and prevention of misdiagnosis. Comprehensive pathological evaluation plays a pivotal role in effective disease management, control of transmission, and improvement of canine health, particularly in stray and free-roaming dog populations.
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