Social isolation stress impairs the resistance of mice to experimental liver metastasis of murine colon 26-L5 carcinoma cells

Our previous study has demonstrated that the exposure of male BALB/c mice t o social isolation stress caused a suppressed immune response and enhanced liver metastasis of colon 26-L5 carcinoma cells. To more precisely understa nd the influence of psychosocial factors on the metastatic process, here we have investigated the effect of social isolation stress on the vulnerabili ty of the host to develop liver metastasis of colon 26-L5 tells, including the time span and incidence of metastatic formation, survival time and chem otherapy response. Isolation stress decreased the time period required for the metastasis formation relative to that in controls. On day 7 after the t umor injection, the 75% incidence of tumor metastasis in the stressed mice was 5 times the 15% incidence in the unstressed mice. When exposed to the c hallenge of lower cell numbers (0.025, 0.05, 0.1 x 10(4)/mouse) of colon 26 -L5 cells, mice subjected to isolation stress developed an elevated inciden ce of metastasis (33.3, 66.6, and 100%, respectively) as compared with the controls (0, 33.3 and 50%, respectively), The survival time following the t umor inoculation was also shorter in the stressed mice (21.83 +/-1.59d) tha n in the control mice (24.08 +/-1.68 d), Furthermore, the response of liver metastasis to chemotherapy consisting of 2 mg/kg cisplatin (CDDP) was wors e in the stressed mice than that in unstressed mice. These findings suggest ed that social isolation stress could significantly impair the resistance o f mice to the development of metastasis.