The relationship between tumor volume and local invasiveness in feline injection-site sarcoma : a retrospective CT study on 200 cases

Introduction/Purpose: Feline Injection-Site Sarcoma (FISS) is a locally invasive and rapidly growing tumor. Computed Tomography (CT) is widely used in the preoperative setting for a clinical staging. However, CT can also demonstrate the volume of the mass. The aim of the present study was to retrospectively analyze the CT features of 200 cases of FISS and to assess whether a statistical relationship between the volume mass and the local invasiveness of the FISS exists. Materials and Methods: CT images and medical records of 200 cases of FISS were retrospectively reviewed. Diameter and volume of the mass were measured on CT (Tomographic Diameter, TD, and Tomographic Volume, TV) and compared to the diameter and volume measured during previous clinical examination (Clinical Diameter, CD, and Clinical Volume, CV). Statistical analyses were performed on SAS 9.1 software to evaluate the influence of tumor variables (localization, presentation, aspect of the mass, number of involved muscles, involvement of underlying bones, presence of skip metastasis, of enlarged lymph nodes, of radiographic or histologic evidence of lung metastasis), and animal variables (breed, gender, age and body weight of the cat) on clinical and tomographic measurements (CD, CV, TD and TV). Values of P < 0,05 were considered significant. Results: The difference between CD and TD and between CV and TV were not statistically significant. A statistical association between the mean diameter (mean of the CD and TD) and each tumor variable was observed. A statistical association was also observed for mean volume (mean of the CV and TV) and each tumor variable. A greater diameter and volume were associated to interscapular localization, first presentation, heterogeneous aspect, greater number of involved muscles, involvement of underlying bones, increased volume of lymphnodes. Lower diameter and volume were associated to radiographic or histologic evidence of pulmonary metastasis. No statistical association was observed between any animal variable and mean diameter/mean volume. Discussion/Conclusion: No significant difference has been observed between clinical and tomographic tumor measurements. The volume of FISS is related to the local invasiveness. In particular, a larger mass is more invasive locally, involving a greater number of muscles and interesting the underlying bones. The greater volume is also associated to increasing in volume of lymph nodes; this result suggests further diagnostic steps, but it does not necessarily imply metastatic involvement. In this study, the lower volume was associated to a more frequent rate of pulmonary metastatization. However, within the group with lung metastasis, 35% of animals were not at first presentation. Furthermore, histologic confirmation was not always available.