Natural killer (NK) cell activity of women with gross cystic disease is inhibited in vitro by breast cyst fluid.

Gross cystic disease (GCD) represents an advanced form of fibrocystic disease of the breast. Bearers of macrocysts have been reported to be at risk of developing breast cancer. Natural killer (NK) cells are a lymphocyte subset deeply involved in immunosurveillance against neoplasia. We investigated whether breast cyst fluid (BCF) aspirated from patients with GCD could affect in vitro the spontaneous and lymphokine-inducible NK activity of peripheral blood mononuclear (PBM) cells concomitantly drawn from the same patients. PBM cells exposed to BCF were evaluated by a standard cytotoxic assay, using K562 cells as a target, in the presence or absence of lymphokines. In vitro incubation of PBM cells with BCF resulted in a consistent decrease of NK cell activity (mean level of suppression about 50%; p < 0.001). Furthermore, exposure of PBM cells to BCF completely prevented the IFN-gamma-dependent enhancement and consistently reduced the IL-2-induced NK activity (p < 0.01). The phenomenon was more apparent for type II cyst BCF. Our data are compatible with an immunosuppressive effect of BCF, potentially leading to altered "local immunosurveillance".