Prevalence of serologic reactivity against four strains of mouse mammary tumour virus among US women with breast cancer

Mouse mammary tumour virus (MMTV) causes breast cancer in mice, and MMTV-specific antibodies develop to high titers among mice infected as adults. Whether MMTV or a related virus infects humans is uncertain, because MMTV DNA sequences have been detected inconsistently and because serologic methods have varied widely. The current study used immunoblot and immunoprecipitation with four strains of MMTV (RIII, FM, C3H, and LA) to detect specific antibodies in 92 sera from US women with breast cancer and in masked dilutions of monoclonal hybridoma and hyperimmunised goat positive-control reagents. In these positive controls, MMTV antibodies of the expected molecular weights were detected at high titer (1 : 100 in the monoclonal reagent, 1 : 10000 in the hyperimmunised goat serum). Nearly 30% of the sera from women with breast cancer had at least one faint band on an immunoblot, but none of these matched the molecular weight of bands revealed by probing the same blot strips with the goat serum. The goat serum readily immunoprecipitated MMTV antigens from all four strains of MMTV, but MMTV antigens were not immunoprecipitated by any of the six breast cancer sera that had four or more nonspecific immunoblot bands. Thus, among women with breast cancer, we found no MMTV-specific antibodies. The upper 95% confidence limit implies that MMTV seroprevalence among breast cancer patients does not exceed 3%.