Comparative Study of Chemically Induced Renal Mesenchymal and Mammary Tumors in Female Sprague-Dawley and Wistar Rats

This study compared the susceptibility of female Sprague-Dawley (SD) and Wistar-Hannover (WH) rats to chemically induced renal mesenchymal tumors (RMTs) and mammary tumors (MTs). Twenty-one-day-old female rats of each strain received a single dose of N-methyl-N-nitrosourea (MNU). The appearance of palpable tumors was assessed weekly until the animals reached 250 days of age. The incidence rates for both RMTs and MTs were 40% (WH) and 12% (SD) and 92% (SD) and 16% (WH), respectively. Female SD rats developed a high incidence (P < .001) of MTs positive for estrogen receptor-alpha (ER-α) and progesterone receptor (PR), showing a short latency, rapid growth, and early euthanasia, resulting in a low number of RMTs. Female WH rats developed a low incidence of MNU-induced MTs associated with a long latency. In contrast, they exhibited a high incidence (P = .053, trend) and number of slowly growing RMTs, which showed variable immunopositivity for vimentin and alpha-smooth muscle actin (α-SMA). The female SD rat strain was more susceptible to developing MTs, whereas the female WH rat strain was more suitable for developing RMTs.