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Vaccine-Associated Fibrosarcomas in Cats

Jul 26, 2018

Vaccine-associated fibrosarcomas (VAS) are tumors of connective tissue that develop at sites of previous vaccinations. Vaccine associated fibrosarcomas (VAS) are thought to develop in 1/1000 to 1/10,000 cases. The time it takes for a tumor to develop after a vaccine can be anywhere from 4 months to over 10 years. These tumors typically behave in a very aggressive fashion. These tumors can extend up to 5 cm beyond the margins of the tumor and there is evidence of metastasis (disease that has spread) at diagnosis in approximately 12% of the cases.  These tumors invade through tissue planes sending out projections of tumor cells much like the roots of a tree. Due to this fact, complete surgical excision can be difficult and the mass that is visible on the skin is usually only the “tip of the iceberg” as there can be a significant amount of disease below the surface. VAS are more locally aggressive (30-70% recurrence rates) and systemically aggressive (~25% metastatic rate) than fibrosarcomas that are not caused by vaccinations.