Introduction

Spontaneous testicular tumors occur most commonly in older dogs. The canine testicular tumors are germ cell tumors (seminoma, teratoma, embryonal carcinoma), sex cord-stromal tumors (Sertoli cell tumors and interstitial (Leyding) cell tumors) and mixed germ cell-sex cord stromal tumor. Seminoma is the only one of the germ cell tumors that occurs frequently in the testicles of the domestic animals. The aim of this study was to investigate whether some tumor markers (1, 2, 3), which are commonly used in diagnostic human pathology, could be demonstrated by immunohistochemical methods in routinely processed tissue samples of canine testicular tumors.

Materials and methods

Samples were collected from testicular tumors removed surgically from dogs during the last five years. The samples consisted of formalin-fixed, paraffin wax-embedded tissue from 21 tumors: 14 seminomas, five Sertoli cell tumors and one interstitial cell tumor. One more was diagnosed as mixed germ cell-sex cord stromal tumor. Sections from each tumor were stained with haematoxylin and eosin, and the histological diagnosis was based on the classification by WHO. Serial 5μm sections were stained immunohistochemically and the primary antibodies used were mouse antiserum against PCNA (Oncogene), p53 and ki-67 (Dako). Immunohistochemical analyses were also performed on three normal canine testis.

Results

Each of the 14 seminomas showed strong nuclear reactivity with PCNA. 9 of 14 seminomas were positive for p53 and the ki-67 immunostaining was expressed only in one of them. All the Serotli tumor cells were stained strongly for PCNA, three of them stained for p53 and only two of them stained with the ki-67. The interstitial (Leyding) cell tumor was stained with all examined antibodies. The mixed tumor sample stained only for PCNA. In the normal testis of the dog, specific nuclear staining for PCNA and p53 proteins were present in all germ cells.

Discussion

Our results suggested that quantitation of PCNA-positive nuclei provides an objective method for assessing proliferative activity in testicular tumors. Concerning the p53 protein the high levels of p53 accumulation were associated with the expression of wild-type p53 and in association with PCNA are useful prognostic markers for canine testicular tumors. Our results indicated that the proliferation rate, assessed by ki-67 immunostaining, is not a predictive marker for outcome in testicular tumors.

References

1. Moore BE, et al (2001): p53: a good diagnostic marker for intratubular germ cell neoplasia, unclassified. Appl Immunohistochem Mol Morphol 9(3): 203-206.

2. Sarli G, et al (1995): Assessment of Proliferative Activity by Anti-PCNA Monoclonal Antibodies in Formalin-fixed, Paraffin-embedded Samples and Correlation with Mitotic Index. Vet Path 32:93-96.

3. Stattin P et al (1997): Cell proliferation assessed by Ki-67 immunoreactivity on formalin fixed tissues is a predictive factor for survival in prostate cancer. J Urol 157(1): 219-222.