The Sprague-Dawley strain of laboratory rat has shown to develop tumors at greater rates regardless of diet or living conditions.
Suzuki H, Mohr U, Kimmerle G. Spontaneous endocrine tumors in Sprague-Dawley rats. J Cancer Res Clin Oncol. 1979 Oct;95(2):187-96. doi: 10.1007/BF00401012. PMID: 521452.
(CANCER RESEARCH 33, 2768-2773, November 1973] Spontaneous Tumors in Sprague-Dawley Rats and Swiss Mice1 J. D. Prejean, J. C. P