Comparison of Argyrophilic Nucleolar Organizer Regions (AgNORs) and Mitotic Index in Distinguishing Benign from Malignant Canine Smooth Muscle Tumors and in Separating Inflammatory Hyperplasia from Neoplastic Lesions of the Urinary Bladder Mucosa

Abstract

Abstract. Staining for argyrophilic nucleolar organizer regions (AgNORs) has proven useful in differentiating recurrent or malignant neoplasms from less aggressive or benign ones. We applied this stain to benign and malignant smooth muscle tumors and to hyperplastic and carcinomatous lesions in the urinary bladder of dogs in an effort to determine its utility in diagnostic situations. The stain was simply performed, and the results were repeatable for different staining intervals and between staining batches. For smooth muscle tumors, enumeration of AgNORs in 100 nuclei was about as efficient as mitotic index in correctly categorizing histologically benign and malignant neoplasms. The mean number of AgNORs/100 nuclei for leiomyomas was significantly less than that obtained for leiomyosarcomas and significantly greater than that obtained for normal smooth muscle. Counts for smooth muscle tumors correlated with the mitotic indexes. Counts by an individual observer were repeated without introducing significant variation, but there was variability between observers, particularly in AgNOR counts for leiomyosarcomas. AgNORs were not useful in separating hyperplastic or polypoid cystitis from transitional cell carcinoma, misclassifying both. Mean AgNOR counts for these 2 conditions did not differ at the 5% level of significance; mitotic index was more efficient at separating the 2 conditions. There was no correlation between mitotic index and AgNOR in urinary tract mucosal specimens. This easily prepared stain may be useful in separating benign and malignant smooth muscle tumors, although AgNORs were less contributory to diagnosing mucosal lesions of the urinary bladder of dogs.Nucleolar organizer regions are focal aggregates of intranuclear nonhistone proteins that are associated with potential sites of ribosomal DNA transcription. 18These proteins are easily localized by virtue of their argyrophilia, hence the acronym AgNOR (argyrophilic nucleolar organizing region). The mean number of AgNORs per nucleus accurately correlates with mitotic rate in tumor cell lines 21 and AgNOR counts may thus provide an indirect measurement of mitotic rate in surgical specimens that is free of the bias produced by postexcisional handling of tissue. The stained complex corresponds ultrastructurally to the binding sites of RNA polymerase 1 and associated proteins regulating transcription and posttranslational modification of ribosomal RNA. 6Measurement and enumeration of AgNORs have been useful in prognosticating the behavior of a variety of neoplasms of humans, particularly in instances where

Pulmonary leiomyosarcoma in a 13‐year‐old Thoroughbred stallion presenting as a differential diagnosis to recurrent airway obstruction

“…Leiomyosarcomas are nonencapsulated invasive tumours formed by densely packed, relatively homogenous spindle cells that retain many features of normal smooth muscle cells (Cooper and Valentine 2002), in contrast to leiomyomas, which are discrete, nonencapsulated, noninvasive tumours. Mitoses were infrequently seen in our case compared to the 1-2/400x field reported in canine leiomyosarcoma (Johnson et al 1995), which could be speculated as being a reason for the delay in appearance of terminal signs of epistaxis in our case.…”

Ureteral Fibroepithelial Polyps in Four Dogs

“…This disease may be a variation of canine polypoid cystitis2' or inflammatory hyperplasia of the urinary bladder in dogs. 22 Masses located in the upper ureter, particularly in an intact or recently castrated middle-aged to older male dog, are likely to be fibroepithelial polyps. This should be a consideration prior to surgical management as local resection can be curative.…”

Uterine leiomyosarcoma in a wild rat (Rattus norvegicus): usefulness of Ki-67 labeling index for diagnosis

“…The neoplastic cells were well-differentiated, uniformly similar to the morphology of normal smooth muscle cells without prominent atypia. In addition, mitotic figures were very rare, with the index being no higher than 5 mitoses/10 HPF, which is an average mitotic index of canine leiomyoma [1,7]. These characteristics correspond to the benign smooth muscle tumor, leiomyoma.…”