Occurrence of antibody against intracytoplasmic A-particles of mouse mammary tumor virus in sera from breast cancer patients.

Acetone-fixed smears of DBA/2 mouse leukemia cells that produce clusters of intracytoplasmic A-particles (pronucleocapsids of mouse mammary tumor virus) were employed as an indirect immunofluorescence system to detect the antibody to A-particles in human sera. With positive test sera, specific fluorescence was easily detectable as discrete cytoplasmic granules at the site of A-particle clusters. The antibody was found in 26 (60%) out of 43 breast cancer patient sera and 4 (25%) of 16 mammary fibroadenoma patient sera, while only 4 (11%) out of 37 control woman sera were antibody-positive. In the case of breast cancer patients, occurrence of tha antibody was not specifically related to a particular type of tumor histology. In a considerable number of positive cases, the antibody tended to disappear within various lengths of time after surgical operation of the breast cancer.