Spontaneous lesions in control B6C3F1 mice and recommended sectioning of male accessory sex organs

Because sampling of the paired lobes (ventral, dorsal, lateral, and anterior) of the mouse prostate has often been inconsistent, comparisons among different investigations have lacked validity. The absence of site identification for prostatic lesions has made reported incidences relatively nonspecific. We present here the lobe-specific incidences and degree of severity of spontaneous lesions in prostate, coagulating gland (anterior prostatic lobe), seminal vesicles, and ampullary glands in 612 control B6C3F1 mice from 12 recent National Toxicology Program 2-year carcinogenicity and toxicity studies conducted in 1 of 4 different laboratories. Lymphocytic infiltration, inflammation, epithelial hyperplasia, mucinous cyst, and mucinous metaplasia were observed in the dorsolateral lobes. Lymphocytic infiltration, inflammation, epithelial hyperplasia, and edema were present in the ventral lobes. Lymphocytic infiltration, acinar dilatation, inflammation, epithelial hyperplasia, and atrophy occurred in the coagulating glands. No neoplastic lesions were observed in the prostate or coagulating gland. Lymphocytic infiltration, acinar dilatation, inflammation, atrophy, adenoma, adenocarcinoma, and a granular cell tumor were observed in the seminal vesicles. Lymphocytic infiltration was also present in the ampullary glands. The results of our survey indicate that the amounts of glandular tissues were not present consistently in slides from the different laboratories. Landmarks for uniform tissue trimming are needed. We therefore suggest an optimal trimming and embedding method for mouse prostate and seminal vesicles to ensure adequate, consistent sampling.