Pathological Characterization of Canine Leydig Cell Tumors: Histomorphological and Immunohistochemical Findings

Introduction: The intact canine population has produced a group of tumors called LCT (e.g., benign until recently), but recent studies have indicated that some LCTs have features consistent with malignancy (i.e., vascular invasion, increased mitotic activity, necrosis). This publication provides a basis for future investigation of LCTs, through a review of relevant literature, and utilizes combinations of modern diagnostic criteria and a comparative pathology approach. By comparing the histological behavior of LCTs using immunohistochemistry, we will develop an increased understanding of the biology of these tumors, allowing for improved clinical prognostication. Methods and Materials: The authors conducted a retrospective analysis of ۱۴ Leydig cell tumors included in a total of ۲۷ canine testicular neoplasms diagnosed from ۲۰۱۲ to ۲۰۲۴, in order to evaluate the common characteristics of Leydig cell tumors. The various characteristics evaluated include size, distribution, and gross pathology. Histologically, the authors examined the histomorphology of the tumors, the number of mitotic figures/۱۰ high power fields (HPFs), the degree of pleomorphism, presence of necrosis, and invasion of the capsule or blood vessels. The authors confirmed the Leydig cell origin of the neoplasm using an immunohistochemical technique, employing inhibin-α and melan A, while Ki-۶۷ was utilized to create proliferation indices. The relationship between the Ki-۶۷ expression and other histological markers of malignancy was evaluated using statistical methods. Results and Discussion: The average age was eleven years. Tumor sizes were ۱.۲ to ۵.۵ cm in diameter. Neoplastic cells were polygonal with an abundance of eosinophilic cytoplasm. The mitotic figures ranged from zero to five per ten high-power fields (HPF) in the cases studied. Five of the cases (۳۵.۷%) exhibited necrosis and three (۲۱.۴%) had vascular invasion. The Ki-۶۷ index ranged from ۱%-۱۸%, with the higher Ki-۶۷ indices tending to result in a more malignant behavior of the tumors. Among two cases with Ki-۶۷ indices greater than ۱۰%, both showed recurrence on follow-up. The findings question the assumption that canine LCTs are harmless and benign. As with other tissues, most LCTs show either low mitotic activity or do not metastasize; however, some show signs of malignant potential. There are also many examples in human medicine where tumors larger than ۵cm or with a Ki-۶۷ index greater than ۱۰% require closer follow-up. Using IHC data to assess prognostic potential informs treatment decisions. This study has reported that dogs with evidence of vascular invasion and necrosis had increased Ki-۶۷ indices, supporting previous studies. These findings suggest that combining standard histopathological examination with histopathological evidence of proliferation is important for identifying and monitoring malignancy in canine LCTs.

کلیدواژه ها:

Canine testis ، Leydig cell tumors ، Histopathology ، Histopathology ، Malignant potential