S294reports of practical oncology and radiotherapy 1 8 ( 2 0 1 3 ) S289-S305 "tumoral repopulation", "radiotherapy delays", "treatment interruptions", "overall treatment time", etc. Additionally, we traced the bibliographic references indicated in the articles previously selected. Special attention was paid in the quality of data reported, carefully divided into univariate or multivariate analysis. Results. Fifty-five papers were considered to fit the purposes of the present study: 49 original data from retrospective series and 3 were pooled-data analysis of previously published series, with a median of 426 patients per article (range 42-4668). The other 3 papers included one editorial, one commentary and a literature review. Larynx was the most frequently reported site (22 articles, 40%), followed by mixed locations (19 articles, 35%) and oropharynx (5 articles, 9%). The majority of the original and pooled-data studies (46/52-88.4%) showed some evidence of a negative relationship between OTT prolongation and LRC or SV. From 50 articles that analyzed LRC, 44 (88%) showed a significant deleterious effect of OTT prolongation, 27 of them by multivariate analyses. And from 16 articles reporting SV data, 14 (87.5%) showed the same effect, 10 of them by multivariate analyses. Conclusions. Consistent evidence exists about a negative outcome in LRC and SV, when OTT is prolonged during a RT course for H&NC. Over 88% of the studies reporting LRC and/or SV endpoints showed its detrimental effect, mostly by multivariate analysis of restrospective data. Taking into account the overwhelming ethical difficulties to perform any randomized clinical trial, prospective or retrospective observational studies are the unique evidence available to deal with this important issue.http://dx.

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