The pATM Immunofluorescence assay: a high-performance radiosensitivity assay to predict post radiotherapy overreactions
A new statistical analysis was performed on 117 patient-specific fibroblasts lines cultured from a skin biopsy in order to assess AUC, sensitivity, specificity, the positive predicted value and the negative predicted value of the pATM Immunofluorescence assay to sort overreactors. The pATM assay shows the highest predictive performance amongst the available tests.
Identifying prior treatment, the patients who will overreact to radiotherapy (RT) would have sound positive clinical implications. By focusing on DNA double‑strand breaks (DSB) recognition and repair proteins after irradiation, we recently demonstrated that the maximal number of pATM nuclear foci in the first hour (pATMmax) after ex vivo irradiation correlated with post‑RT toxicity severity. We aimed to carry out additional analyses on our whole collection of fibroblast lines to refine the predictive performance of our assay.
Immunofluorescence experiments were performed on 117 primary skin fibroblast lines irradiated at 2 Gy. The toxicity response was split up into two binary classes: 0 if toxicity grade < 2 and 1 otherwise. To assess the relationship between the quantity of pATMmax foci and toxicity grade, we applied a correlation then a supervised classification analysis. Training datasets from 13 radiosensitive patients randomly drawn with a random under-sampling technique were constituted. ROC analyses were performed with a Monte-Carlo method to estimate the optimal threshold and discriminate the responses for each data set. The discrimination cut-off was estimated as the maximum value of the 104 thresholds computed from each training subset.
As expected, we confirmed a quasi linear dependence between toxicity and pATMmax (Fig 1A & 1B; Pearson correlation coefficient: -0.85; p < 2.2e−16). When taken as a binary predictive assay with the optimal cut‑off value of 34.5 pATM foci/cell, our assay showed an outstanding predictive performance with the following values respectively for sensitivity, specificity, NPV, PPV and AUC: 1.00, 0.92, 1.00, 0.99 and 0.987.
The results of these experiments allowed us to identify pATMmax as a high performance predictive parameter of post‑radiotherapy OR. Additional studies are in progress to confirm that this radiosensitivity assay reaches the same performances in any condition to adapt the clinical practice.
 G. Vogin, T. Bastogne, L. Bodgi, J. Gillet-Daubin, A. Canet, S. Pereira, and N. Foray, “The pATM Immunofluorescence assay: a high-performance radiosensitivity assay to predict post radiotherapy over- reactions.,” International Journal of Radiation Oncology - Biology - Physics, vol. 101, no. 3, pp. 1–8, 2018.