Canine Transmissible Venereal Tumor: A Review

Abstract

Canine transmissible venereal tumor (TVT) is a commonly occurring tumor of dogs affecting both sexes. It is common in dogs which have an uncontrolled sexual behavior with incidence ranging from 2 to 43 percent of all tumors in temperate climates. The etiology appears to be cell transplant from affected to unaffected dogs. The pathogenesis, gross and microscopic findings, diagnosis, prognosis and therapies have been reviewed. Gross findings of small nodule like lesions which bleed is the most consistent clinical finding. Smears made from the tumor reveal round cells with vacuoles and mitotic figures. The tumor is many times self limiting and vincristine sulfate is currently considered the most effective therapy. The use of vincristine sulfate in male dogs must balance the potential benefits to the patient and the interest in using the animal for breeding as vincristine sulfate impairs the semen quality. Immune therapy of TVT is still to be validated for clinical use. Transmissible venereal tumor (TVT), also known as infectious sarcoma, venereal granuloma, transmissible lymphosarcoma or Sticker tumor is a benign reticuloendothelial tumor of the dog that mainly affects the external genitalia and occasionally the internal genitalia. As it is usually transmitted during coitus (Tella et al., 2004) it mainly occurs in young, sexually mature animals (Rogers, 1997).It is transplanted during coitus with intact viable cells across major histocompatibility complex (MHC) barriers within the same species (Mukaratirwa and Gruys, 2003) and even to other members of the canine family, such as foxes, coyotes and jackals (Higgins, 1966). Laboratory transplantation of TVT from one dog to other using viable cells is also possible ( Yang and Jones, 1973). TVT cells contain an abnormal number of chromosomes ranging from 57 to 64 and averaging 59, in contrast to the normal 78 of the species. Metastasis of TVT is uncommon, only occurring in puppies and immuno-compromised dogs. The uniqueness of TVT lies in the fact that this is the only proven example of a naturally occurring tumor that is transmitted as an allograft by cell transplantation, and the tumor becomes autonomous from the original host. In other words, the the tumor behaves like a parasite. This kind of tumor developed only in the dog, probably because during coitus there is extensive abrasive abrasions and bleeding of the penile mucosa and vagina, making transplantations of the tumor easy. Because TVT can be easily transplanted investigations on various aspects of tumor biology have been done to provide clues to similar phenomenon that occur in other animal and human tumors. Thus TVT has been studied extensively. A very interesting aspect that has attracted attention of TVT is the role of the host’s immune response during the progressive and regressive stages of the tumor. The capacity of immunologic response of the host has a main role in the expansion of such tumors (Cohen, 1973) with an increase in severity seen in immunologically compromised animals. In this review some known facts of TVT have been reviewed.