Comparison between May‐Grünwald‐Giemsa and rapid cytological stains in fine‐needle aspirates of canine mast cell tumour: Diagnostic and prognostic implications

Abstract

Mast cell tumours (MCTs) are often diagnosed by cytology based on the identification of purple intracytoplasmic granules with methanolic Romanowsky stains, including May-Grünwald-Giemsa (MGG). In clinical practice, aqueous rapid stains (RS) are commonly used, but mast cell granules may not stain properly. Aim of this prospective study was to investigate the frequency of MCT hypogranularity with RS and its potential implications in tumour identification, cytological grading assessment and recognition of nodal metastatic disease. Cytological preparations of canine primary MCTs and metastatic lymph nodes with subsequent histopathological confirmation were included. For each case, good-quality smears were stained with both MGG and RS and comparatively assessed. Eleven of 60 (18.3%) primary MCTs were hypogranular with RS; 9 of them were histologically high-grade tumours and in 3 cases (5%) a definitive MCT diagnosis could not be made. Accuracy in cytological grading assessment (85%) did not differ between RS and MGG. Thirteen of 28 (46.4%) metastatic lymph nodes were hypogranular with RS and 3 independent observers failed to identify nodal MCT metastases in 7% to 18% of RS-stained smears. This study confirms that, in limited cases, RS can be ineffective in staining MCT granules, particularly in high-grade tumours, thus making diagnosis more dependent on experience and quality of preparations. In dubious cases, methanolic stains should be applied. The use of RS is discouraged for the search of nodal metastases, as the identification of isolated mast cells can be more challenging.

Value, Limitations, and Recommendations for Grading of Canine Cutaneous Mast Cell Tumors: A Consensus of the Oncology-Pathology Working Group

“…These OPWG members include 6 board-certified veterinary oncologists (DB, JBF, CAC, LG, JI, PJ), 3 board-certified veterinary anatomic pathologists (RR, DAK, AP), 1 board-certified veterinary clinical pathologist (RP), and 1 board-certified veterinary surgeon (JML). All subgroup members separately and critically reviewed the same publications, 1,2,5,6,8,9,[16][17][18][19][20][21][22][23] but to expedite the last update including 6 publications 1,5,8,9,16,19 the members were divided into 2 groups reviewing 3 papers for each group. Each member independently completed a template for each respective article providing a summary of the study objective, study design, materials and methods, and a critical assessment of the statistical soundness and conclusions drawn, while also offering their own overall conclusions and assessment relative to the strength and merit of the study.…”

“…1,9 Most studies not providing that information were published before it was recognized that the MC should be reported using a standardized area. 2,6,8,[16][17][18][19][20][21][22][23] For future studies, standardization of the parameters for MC assessment in cutaneous MCTs is considered to be of paramount importance. Defining the best method for selecting the region of highest mitotic activity within each tumor should be emphasized, as interpathologist variability in identifying these "hot spots" has been recently documented.…”

“…4 The diagnostic cornerstone for determining the prognosis of canine cutaneous MCTs has been for many years and still is the histological grade with a considerable number of publications available in the literature on this topic. 1,2,[4][5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23] The Oncology Pathology Working Group (OPWG) is a joint initiative of the Veterinary Cancer Society and the American College of Veterinary Pathologists. This group aims to promote an integrated working relationship between veterinary oncologists and pathologists to facilitate and ensure the highest standard of pathology support and reporting for the advancement of veterinary clinical oncology and cancer research.…”

“…Since then, additional articles on grading of canine cutaneous MCTs have been published, continuing to expand and improve the body of knowledge on the subject. 1,5,8,9,16,19 This article represents the most recently updated OPWG consensus on grading of canine cutaneous MCTs, and it was approved by the OPWG membership at large in June 2020. The concluded recommendations represent the opinions of the authors, with the support of the OPWG membership, based on critical review of the literature as determined by assessing the robustness of the data presented in the publications reviewed.…”

Τhe Effect of Opioid Administration on Cytologic and Histopathologic Diagnosis of Canine Cutaneous Mast Cell Tumors Treated by Surgical Excision

“…Fine needle aspiration (FNA) cytology can provide a straight-forward diagnosis of these tumors in almost all cases. Their distinctive intracytoplasmic granules can be observed in smears, from even poorly differentiated neoplasms [ 6 ].…”