CTVT

Canine transmissible venereal tumor (CTVT) is a contagious cancer of dogs caused by a clonal line of cancer cells that is transmitted between individuals through mating or close physical contact. It is one of the best-described naturally occurring transmissible cancers in mammals.

Origin and biology: CTVT began from a single dog's tumor and has persisted as a living cancerous graft that can colonize new hosts. The tumor cells themselves are transferred between dogs and can evade initial immune responses, allowing establishment and growth. In many dogs, the immune system eventually controls or eliminates the tumor, leading to regression.

Transmission and presentation: The primary mode of transmission is sexual contact, but nonsexual transmission through licking, biting, or close contact can occur. Lesions most commonly develop on genitalia or mucosal surfaces, though extragenital sites such as the oral cavity, nasal mucosa, or skin can be involved. Lesions may appear as nodular, ulcerated, or cauliflower-like masses and can progress if left untreated.

Diagnosis and treatment: Diagnosis relies on cytology or biopsy showing characteristic malignant round cells with high mitotic activity; immunohistochemistry or molecular methods can support the diagnosis. The standard treatment is chemotherapy, with vincristine as a common first-line agent; many dogs respond within weeks to months. Alternative regimens, including doxorubicin, are effective in some cases. Spontaneous regression occurs but is not reliable.

Prognosis and distribution: CTVT has a worldwide distribution, particularly where free-roaming dog populations are common. With timely treatment, prognosis is excellent; untreated tumors can persist and cause morbidity. CTVT is often cited as a notable example of a naturally transmissible cancer in mammals.