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Background  The prognostic value of histone γ-H2AX and 53BP1 proteins to predict the radiotherapy (RT) outcome of patients with rectal carcinoma (RC) was evaluated in a prospective study. High expression of the constitutive histone γ-H2AX is indicative of defective DNA repair pathway and/or genomic instability, whereas 53BP1 (p53-binding protein 1) is a conserved checkpoint protein with properties of a DNA double-strand breaks sensor.    Methods  Using fluorescence microscopy, we assessed spontaneous and radiation-induced foci of γ-H2AX and 53BP1 in peripheral blood mononuclear cells derived from unselected RC patients ( n  = 53) undergoing neoadjuvant chemo- and RT. Cells from apparently healthy donors ( n  = 12) served as references.    Results  The γ-H2AX assay of  in vitro  irradiated lymphocytes revealed significantly higher degree of DNA damage in the group of unselected RC patients with respect to the background, initial (0.5 Gy, 30 min) and residual (0.5 Gy and 2 Gy, 24 h post-radiation) damage compared to the control group. Likewise, the numbers of 53BP1 foci analyzed in the samples from 46 RC patients were significantly higher than in controls except for the background DNA damage. However, both markers were not able to predict tumor stage, gastrointestinal toxicity or tumor regression after curative RT. Interestingly, the mean baseline and induced DNA damage was found to be lower in the group of RC patients with tumor stage IV ( n  = 7) as compared with the stage III ( n  = 35). The difference, however, did not reach statistical significance, apparently, because of the limited number of patients.    Conclusions  The study shows higher expression of γ-H2AX and 53BP1 foci in rectal cancer patients compared with healthy individuals. Yet the data  in vitro  were not predictive in regard to the radiotherapy outcome.    Electronic supplementary material  The online version of this article (doi:10.1186/s12885-015-1890-9) contains supplementary material, which is available to authorized users.

A prospective study on histone γ-H2AX and 53BP1 foci expression in rectal carcinoma patients: correlation with radiation therapy-induced outcome