Higher levels of antibodies to the tumour‐associated antigen cyclin B 1 in cancer‐free individuals than in patients with breast cancer

Summary C yclin B 1 is a checkpoint protein that regulates cell division from G 2 to the M phase. Studies in mice have shown that cyclin B 1 vaccine‐induced immunity significantly delayed or prevented the spontaneous cancer development later in life. We hypothesized that if these results showing a protective effect of anti‐cyclin B 1 antibodies could be extrapolated to the human condition, cancer‐free individuals should have higher levels of endogenous antibodies than patients with cancers characterized by the over‐expression of this tumour‐associated antigen. To test this hypothesis, we characterized a large (1739 subjects) number of multi‐ethnic patients with breast cancer (which over‐expresses cyclin B 1) and matched controls for anti‐cyclin B 1 immunoglobulin (Ig) G antibodies. Multivariate analyses, after adjusting for the covariates, showed that cancer‐free individuals had significantly higher levels of naturally occurring IgG antibodies to cyclin B 1 than patients with breast cancer (mean ± standard deviation: 148·0 ± 73·6 versus 126·1 ± 67·8 arbitrary units per ml; P  < 0·0001). These findings may have important implications for cyclin B1‐based immunotherapy against breast cancer and many other cyclin B1‐over‐expressing malignancies.