Stereology in Grading and Prognosis of Canine Cutaneous Mast Cell Tumors

Canine cutaneous mast cell tumors (ccMCTs) are currently graded according to Patnaik and Kiupel grading schemes. The qualitative and semiquantitative parameters applied in these schemes may lead to inter- and intraobserver variability. This study investigates the prognostic value of volume-weighted mean nuclear volume ([Formula: see text]), a stereological estimation that provides information about nuclear size and its variability. [Formula: see text] of 55 ccMCTs was estimated using the “point-sampled intercept” method and compared with histological grade and clinical outcome. The clinical history of dogs treated with surgical excision alone was available for 30 ccMCTs. Statistical differences in [Formula: see text] were found between grade II ([Formula: see text] = 115 ± 29 µm(3)) and grade III ccMCTs ([Formula: see text] = 197 ± 63 µm(3)), as well as between low-grade ([Formula: see text] = 113 ± 28 µm(3)) and high-grade ccMCTs ([Formula: see text] = 184 ± 63 µm(3)). An optimal cutoff value of [Formula: see text] ≥ 150 µm(3) and [Formula: see text] ≥ 140 µm(3) was determined for grade III and high-grade ccMCTs, respectively. In terms of prognosis, [Formula: see text] was not able to predict the clinical outcome in 42% of the cases; however, cases with [Formula: see text] <125 µm(3) had a favorable outcome. These results indicate that, despite having limited prognostic value when used as a solitary parameter, [Formula: see text] is highly reproducible and is associated with histological grade as well as with benign behavior.