Impact of stress and levels of corticosterone on the development of breast cancer in rats

José María De la Roca-Chiapas,1 Gloria Barbosa-Sabanero,2 Jorge Antonio Martínez-García,3 Joel Martínez-Soto,1 Víctor Manuel Ramos-Frausto,1 Leivy Patricia González-Ramírez,1 Ken Nowack4 1Department of Psychology, 2Department of Medical Sciences, Division of Health Sciences, Campus Leon-University of Guanajuato, Guanajuato, 3General Regional Hospital of Leon, Guanajuato, Mexico; 4Envisia Learning, Inc., Santa Monica, CA, USA Abstract: Stress is experienced during cancer, and impairs the immune system's ability to protect the body. Our aim was to investigate if isolation stress has an impact on the development of tumors in rats, and to measure the size and number of tumors and the levels of corticosterone. Breast cancer was induced in two groups of female rats (N=20) by administration of a single dose of N-methyl-N-nitrosourea 50 mg/kg. Rats in the control group (cancer induction condition) were allowed to remain together in a large cage, whereas in the second group, rats were also exposed to a stressful condition, that is, isolation (cancer induction and isolation condition, CIIC). The CIIC group displayed anxious behavior after 10 weeks of isolation. In the CIIC group, 16 tumors developed, compared with only eleven tumors in the control cancer induction condition group. In addition, compared with the control group, the volume of tumors in the CIIC group was greater, and more rats had more than one tumor and cells showed greater morphological damage. Levels of corticosterone were also significantly different between the two groups. This study supports the hypothesis that stress can influence the development of cancer, but that stress itself is not a sufficient factor for the development of cancer in rats. The study also provides new information for development of experimental studies and controlled environments. Keywords: breast cancer, corticosterone, isolation condition, psychoneuroimmunology, stres