We monitored a cohort of wild type (herein referred to as Cep55wt/wt, n = 40), heterozygous transgenic (Cep55wt/Tg, n = 40), and homozygous transgenic (Cep55Tg/Tg, n = 50) Cep55 mice (both males and females) over a period of 2.5 years for spontaneous tumor formation. The gene discussed is CEP55; the disease is neoplasm.