Mifepristone treatment improves length and quality of survival of mice with spontaneous lung cancer.

BACKGROUND There are data showing that human leukemia cell lines have mRNA for an immunomodulatory protein found in normal pregnancy that is stimulated by progesterone. One of the functions of this progesterone-induced blocking factor (PIBF) is to suppress natural killer cell activity. Mifepristone has not only been shown to down-regulate PIBF expression by human leukemic cell lines but has also been shown to prolong and improve the length of life of mice with spontaneous leukemia. MATERIALS AND METHODS Mifepristone at 0.3 mg was gavaged three times weekly from 8 weeks vs. olive oil in the controls. RESULTS The survival at one year for mice treated with mifepristone was 57.6% vs. 26.6% for controls (p=0.056). There were 66.7% of mice treated with mifepristone with no sick days whereas there was not one control mouse that did not become sick within the first year. The mean number of days sick was 11.6 for mifepristone vs. 57.6 days for controls (p=0.05) and 66.7% of the survival group had no sick days vs. none of the controls. CONCLUSION These data suggest a possible novel cancer therapy using progesterone receptor antagonist drugs even in tumors not known to have progesterone receptors to try to change the tumor microenvironment and re-activate suppressed natural killer cells.