P‐63. Canine cutaneous mastocytoma: correlation between histological grading, cytological nuclear area and nucleus:cytoplasm ratio

Cutaneous mastocytoma is frequently diagnosed in dogs, representing 9–21% of skin tumors. Due to the unpredictable behavior of the tumor, a majority of clinicians consider it dangerous, with a 50% rate of recurrence and 50% of tumors being malignant. Seventeen dogs of various breeds were diagnosed with mastocytoma, inflammation rich in mast cells and tumors infiltrated with mast cells (canine cutaneous histiocytoma). Fine needle biopsies were performed, and smears were stained with May–Grunwald–Giemsa. Histological sections were stained with trichromic Masson and Luna stains. Nuclear areas and nucleus:cytoplasm ratios were determined using computed morphometry. Measurements were made only from smears. The values were statistically interpreted using Student's t ‐test. According to histological features, four morphological grades were established: Grade 1 (well differentiated), Grades 2 and 3 (intermediary) and Grade 4 (anaplastic). Nuclear area values ranged from 5147 (±427) to 5847 (±169) pixels in Grade 1 mastocytoma, 4563 (±318) to 6619 (±289) pixels in Grades 2 and 3, and 6864 (±257) to 10456 (±773) pixels in Grade 4. Nucleus:cytoplasm ratios were between 0.37 and 0.44 (mean 0.40) in Grade 1, between 0.42 and 0.43 (mean 0.42) in Grades 2 and 3, and between 0.37 – 0.56 (mean 0.46) in Grade 4. Normal mast cells have a nucleus:cytoplasm ratio of 0.27. The variability of nuclear area values does not allow correlation with the histological grading of mastocytomas; therefore, prognosis cannot be estimated by nuclear area values. The average nucleus:cytoplasm ratio increased from Grade 1 through Grade 4 and correlated with the histological grading of canine mastocytomas. Funding: Self‐funded