Clinical and computed tomography tumour dimension assessments for planning wide excision of injection site sarcomas in cats: how strong is the agreement?

The tumour dimensions of injection site sarcoma (ISS) in cats are among the first aspects evaluated for calibrating surgical doses.1 Despite this role, a standardized approach to measuring the size of ISS in cats is currently lacking.2-5 The discrepancy between clinical and computed tomography (CT) measurements of the same tumour may led to possible bias that affects the surgical dose and prognosis analysis. The aim of this study was to investigate prospectively the agreement between clinical and CT measurements of tumour size in newly diagnosed ISS in cats. Fifty-three client-owned cats that underwent both clinical and CT measurements of the length and width of an ISS6 were included. The agreement between two measurements was evaluated with the Bland and Altman approach.7 A measurement of overall concordance using the concordance correlation coefficient (CCC) was obtained. Computed tomography measurements showed a tendency towards being larger than clinical dimensions, both for length and width, and this difference increased with increasing tumour size. The CCC also suggested unsatisfactory concordance between the two measurement methods. This result suggested wider lateral margins of excision in cases of clinical measurements relative to CT evaluation. The excision with 5-cm margins recently proposed for clinical dimensions might not be sufficient in cases of large tumours, leading to the hypothesis that for large palpable tumour a CT evaluation could be more useful for determining the extension of tumour tentacles. The usefulness of contrast-enhanced whole- body CT for ISS in cats is not only linked to the role of planning lateral excision margins, but it also has the ability to estimate deep margins and to detect distant metastasis. These aspects are crucial points to discuss before surgery with surgical staff and the owner.