Abstract
The Crl:CD(SD) Sprague Dawley rat and the Crl:WI(Han) Wistar Hannover (Wistar Han) rat are two outbred rat models commonly used in 2-year carcinogenicity testing. In this presentation, the spontaneous incidences of common, rare, and fatal neoplasms in the two models in 2-year carcinogenicity studies were compared from 51 Sprague Dawley rat studies and 31 Wistar Han rat studies that were completed from 2016 to 2023. All Wistar Han rat studies completed the intended 104 weeks of dosing, whereas 47 of the 51 Sprague Dawley rat studies were terminated early in both sexes or terminated early in one sex. The incidence of total spontaneous neoplasms was greater in Sprague Dawley rats when compared to Wistar Han rats of either sex, with the greatest incidence found in female Sprague Dawley rats (95.93%). Of palpable masses that corresponded to neoplasms, approximately 85–90% of masses were mammary tumors in females of either strain, while a similar percentage of masses corresponded to skin tumors in male rats of either strain. Common fatal tumors included pituitary adenoma of the pars distalis, carcinoma of the pars distalis, mammary adenocarcinoma, and mammary fibroadenoma, and were found at a lower incidence in Wistar Han rats; where calculable, the onset of these neoplasms was earlier in Sprague Dawley rats.
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