Thymic epithelial hyperplasia and thymoma in control rasH2 transgenic mice from 26-week carcinogenicity assays

STP 2026 -- Since the FDA’s approval in 2003, transgenic rasH2 (Tg.rasH2) mice have been used as alternative models to assess the carcinogenic potential of new drug candidates. While several published articles document spontaneous non-neoplastic and neoplastic findings in Tg.rasH2 mice, the incidence and morphologic criteria of proliferative thymic epithelial lesions have not been discussed in detail. Here we report the incidence and diagnostic morphologic criteria of non-neoplastic (epithelial hyperplasia) and neoplastic (benign and malignant thymoma) proliferative findings in the thymus.