Pulmonary and mediastinal metastases of a vaccination-site sarcoma in a cat

Sarcomas at vaccination sites in cats were first reported in 1992. Recent retrospective studies have confirmed an association between these vaccination-site sarcomas (VSS) and feline leukemia virus (FeLV) and/or rabies vaccines. In most cases, VSS are locally invasive fibrosarcomas that tend to recur but rarely metastasize. We report the mediastinal and pulmonary metastases of a VSS in a FeLV- and feline immunodeficiency virus-negative, 8-year-old, domestic short-haired cat. The primary sarcoma was removed from an interscapular vaccination site and diagnosed as a VSS 3 months prior to radiographic lesions suggestive of pulmonary and mediastinal metastases. At necropsy, there were multiple pulmonary and mediastinal nodules that histologically and ultrastructurally were fibrosarcomas, cytomorphologically similar to the VSS. In addition, immunohistochemical staining patterns of the VSS and metastatic sites were consistent with that described for VSS. Recent reports of pulmonary and mediastinal metastases of interscapular VSS emphasize the importance of early diagnosis and treatment of these tumors.