The ratio of initial/residual DNA damage predicts intrinsic radiosensitivity in seven cervix carcinoma cell lines

Evaluation of Capability and Relationship of Different Radiobiological Endpoints for Radiosensitivity Prediction in Human Tumor Cell Lines Compared with Clonogenic Survival

BACKGROUND

Establishing a predictive assay of radiosensitivity (as an appropriate, practical and cost-effective method) has been challenging.

OBJECTIVE

The purpose of this study is to evaluate the capability and relationship of various endpoints, including GammaH2AX, micronuclei; and apoptosis in determining the human tumor cell lines radiosensitivities compared with clonogenic survival.

MATERIAL AND METHODS

In an experimental in-vitro study, the response of carcinoma cell lines of HN5 and HeLa to 2 Gy of 6 MV photon beam was investigated via various assays.

RESULTS

Survival fraction at 2 Gy (SF2) of HeLa and HN5 was indicated as 0.42 ± 0.06 and 0.5 ± 0.03 respectively, proposing more radioresistance of HN5. This finding was confirmed with "2 Gy apoptosis enhancement ratio" which was 1.77 and 1.42 in HeLa and HN5. The increased levels of DNA DSBs were observed after irradiation; significant in HeLa with enhancement rate of 19.24. The micronuclei formation followed an ascending trend post irradiation; but with the least difference between two cells. Although the relationship between micronuclei and clonogenic survival was moderate (R² = 0.35), a good correlation was observed between apoptosis and clonogenic survival (R² = 0.71).

CONCLUSION

The results of studied endpoints agreed with the SF2, highlighting their capabilities in radiosensitivity prediction. In terms of the enhancement ratio, gammaH2AX foci scoring could be a valid indicator of radiosensitivity but not the exact surrogate marker of survival because no correlation was observed. Moreover, considering the chief determents comprising lack of time and money, the apoptotic induction might be an appropriate indicator with the best correlation coefficient.

Evaluation of the Major Steps in the Conventional Protocol for the Alkaline Comet Assay

Single cell gel electrophoresis, also known as the comet assay, has become a widespread DNA damage assessment tool due to its sensitivity, adaptability, low cost, ease of use, and reliability. Despite these benefits, this assay has shortcomings, such as long assay running time, the manipulation of multiple slides, individually, through numerous process steps, the challenge of working in a darkened environment, and reportedly considerable inter- and intra-laboratory variation. All researchers typically perform the comet assay based upon a common core approach; however, it appears that some steps in this core have little proven basis, and may exist, partly, out of convenience, or dogma. The aim of this study was to critically re-evaluate key steps in the comet assay, using our laboratory's protocol as a model, firstly to understand the scientific basis for why certain steps in the protocol are performed in a particular manner, and secondly to simplify the assay, and decrease the cost and run time. Here, the shelf life of the lysis and neutralization buffers, the effect of temperature and incubation period during the lysis step, the necessity for drying the slides between the electrophoresis and staining step, and the need to perform the sample workup and electrophoresis steps under subdued light were all evaluated.

Combined pretreatment with 18F-FDG PET/CT and Comet assay guides the concurrent chemoradiotherapy of locally advanced cervical cancer: study protocol for a randomized controlled trial

Background

Cisplatin-based chemoradiation is the standard of care for patients with locally advanced cervical cancer. Nevertheless, an increasing number of radio-resistant tumors still recur.

Methods and design

Three hundred cervical cancer patients with FIGO stages IB2–IVA and no para-aortic lymphadenopathy (> 10 mm) will be enrolled. All patients will be randomly divided into four arms to receive either (1) intensity modulated radiation therapy (IMRT), (2) RapidArc, (3) positron emission tomography/computed tomography (PET/CT) with F-18 fluorodeoxyglucose (FDG), or (4) Comet assay-guided IMRT, PET/CT, and Comet assay-guided RapidArc. All patients will receive definitive radiotherapy consisting of external beam whole pelvic radiation therapy and high-dose rate intracavitary brachytherapy. Cisplatin 30 mg/m² weekly will be administered concurrently for five courses. Two to four cycles of TP (Taxol 135 mg/m², D1, and DDP 75 mg/m², D1–3) sequential chemotherapy will be performed according to MRI or PET/CT after cisplatin-based chemoradiation. The primary outcome measure is progression-free survival, and the second outcome measures are overall survival and time to progression.

Discussion

RapidArc has an obvious advantage in improving the degree of target coverage, improving organs at risk, sparing healthy tissue, and significantly reducing the treatment time. FDG-PET/CT can increase the agreement between biopsies and delineated tumor volume and has the potential to positively impact the course of treatment. The Comet assay is attractive as a potential clinical test of tumor radiosensitivity. During radiotherapy, accurately defining disease areas is critical to avoid the unnecessary irradiation of normal tissue. Based on FDG-PET/CT and Comet assay, higher doses can be safely delivered to accurate tumor volumes, while the doses to the bladder and rectum are relatively low.

Trial registration

ClinicalTrials.gov Protocol Registration and Results System Receipt Release Date: May 21, 2017 – Retrospectively registered. NCT03163979.

Variations in the Processing of DNA Double-Strand Breaks Along 60-MeV Therapeutic Proton Beams

Purpose

To investigate the variations in induction and repair of DNA damage along the proton path, after a previous report on the increasing biological effectiveness along clinically modulated 60-MeV proton beams.

Methods and Materials

Human skin fibroblast (AG01522) cells were irradiated along a monoenergetic and a modulated spread-out Bragg peak (SOBP) proton beam used for treating ocular melanoma at the Douglas Cyclotron, Clatterbridge Centre for Oncology, Wirral, Liverpool, United Kingdom. The DNA damage response was studied using the 53BP1 foci formation assay. The linear energy transfer (LET) dependence was studied by irradiating the cells at depths corresponding to entrance, proximal, middle, and distal positions of SOBP and the entrance and peak position for the pristine beam.

Results

A significant amount of persistent foci was observed at the distal end of the SOBP, suggesting complex residual DNA double-strand break damage induction corresponding to the highest LET values achievable by modulated proton beams. Unlike the directly irradiated, medium-sharing bystander cells did not show any significant increase in residual foci.

Conclusions

The DNA damage response along the proton beam path was similar to the response of X rays, confirming the low-LET quality of the proton exposure. However, at the distal end of SOBP our data indicate an increased complexity of DNA lesions and slower repair kinetics. A lack of significant induction of 53BP1 foci in the bystander cells suggests a minor role of cell signaling for DNA damage under these conditions.

Investigation of radiosensitivity gene signatures in cancer cell lines

Intrinsic radiosensitivity is an important factor underlying radiotherapy response, but there is no method for its routine assessment in human tumours. Gene signatures are currently being derived and some were previously generated by expression profiling the NCI-60 cell line panel. It was hypothesised that focusing on more homogeneous tumour types would be a better approach. Two cell line cohorts were used derived from cervix [n = 16] and head and neck [n = 11] cancers. Radiosensitivity was measured as surviving fraction following irradiation with 2 Gy (SF2) by clonogenic assay. Differential gene expression between radiosensitive and radioresistant cell lines (SF2 median) was investigated using Affymetrix GeneChip Exon 1.0ST (cervix) or U133A Plus2 (head and neck) arrays. There were differences within cell line cohorts relating to tissue of origin reflected by expression of the stratified epithelial marker p63. Of 138 genes identified as being associated with SF2, only 2 (1.4%) were congruent between the cervix and head and neck carcinoma cell lines (MGST1 and TFPI), and these did not partition the published NCI-60 cell lines based on SF2. There was variable success in applying three published radiosensitivity signatures to our cohorts. One gene signature, originally trained on the NCI-60 cell lines, did partially separate sensitive and resistant cell lines in all three cell line datasets. The findings do not confirm our hypothesis but suggest that a common transcriptional signature can reflect the radiosensitivity of tumours of heterogeneous origins.

Poor prognosis associated with human papillomavirus α7 genotypes in cervical carcinoma cannot be explained by intrinsic radiosensitivity

PURPOSE

To investigate the relationship between human papillomavirus (HPV) genotype and outcome after radiation therapy and intrinsic radiosensitivity.

METHODS AND MATERIALS

HPV genotyping was performed on cervix biopsies by polymerase chain reaction using SPF-10 broad-spectrum primers, followed by deoxyribonucleic acid enzyme immunoassay and genotyping by reverse hybridization line probe assay (LiPA25) (version 1) (n=202). PapilloCheck and quantitative reverse transcription-polymerase chain reaction were used to genotype cervix cancer cell lines (n=16). Local progression-free survival after radiation therapy alone was assessed using log-rank and Cox proportionate hazard analyses. Intrinsic radiosensitivity was measured as surviving fraction at 2 Gy (SF2) using clonogenic assays.

RESULTS

Of the 202 tumors, 107 (53.0%) were positive for HPV16, 29 (14.4%) for HPV18, 9 (4.5%) for HPV45, 23 (11.4%) for other HPV genotypes, and 22 (10.9%) were negative; 11 (5.5%) contained multiple genotypes, and 1 tumor was HPV X (0.5%). In 148 patients with outcome data, those with HPVα9-positive tumors had better local progression-free survival compared with α7 patients in univariate (P<.004) and multivariate (hazard ratio 1.54, 95% confidence interval 1.11-1.76, P=.021) analyses. There was no difference in the median SF2 of α9 and α7 cervical tumors (n=63). In the cell lines, 9 were α7 and 4 α9 positive and 3 negative. There was no difference in SF2 between α9 and α7 cell lines (n=14).

CONCLUSION

The reduced radioresponsiveness of α7 cervical tumors is not related to intrinsic radiosensitivity.

Evaluation of different biomarkers to predict individual radiosensitivity in an inter-laboratory comparison--lessons for future studies

Radiotherapy is a powerful cure for several types of solid tumours, but its application is often limited because of severe side effects in individual patients. With the aim to find biomarkers capable of predicting normal tissue side reactions we analysed the radiation responses of cells from individual head and neck tumour and breast cancer patients of different clinical radiosensitivity in a multicentric study. Multiple parameters of cellular radiosensitivity were analysed in coded samples of peripheral blood lymphocytes (PBLs) and derived lymphoblastoid cell lines (LCLs) from 15 clinical radio-hypersensitive tumour patients and compared to age- and sex-matched non-radiosensitive patient controls and 15 lymphoblastoid cell lines from age- and sex- matched healthy controls of the KORA study. Experimental parameters included ionizing radiation (IR)-induced cell death (AnnexinV), induction and repair of DNA strand breaks (Comet assay), induction of yH2AX foci (as a result of DNA double strand breaks), and whole genome expression analyses. Considerable inter-individual differences in IR-induced DNA strand breaks and their repair and/or cell death could be detected in primary and immortalised cells with the applied assays. The group of clinically radiosensitive patients was not unequivocally distinguishable from normal responding patients nor were individual overreacting patients in the test system unambiguously identified by two different laboratories. Thus, the in vitro test systems investigated here seem not to be appropriate for a general prediction of clinical reactions during or after radiotherapy due to the experimental variability compared to the small effect of radiation sensitivity. Genome-wide expression analysis however revealed a set of 67 marker genes which were differentially induced 6 h after in vitro-irradiation in lymphocytes from radio-hypersensitive and non-radiosensitive patients. These results warrant future validation in larger cohorts in order to determine parameters potentially predictive for clinical radiosensitivity.

Intrinsic radiation sensitivity: cellular signaling is the key

The concept that the balance between DNA damage and repair determines intrinsic radiation sensitivity has dominated radiobiology for several decades. There is undeniably a cause- effect relationship between radiation-induced molecular alterations in the genomic DNA and cellular consequences. In the last decade, however, it has become obvious that the chromatin context affects the fate of damaged DNA and that cellular signaling is an important factor in defining intrinsic radiation sensitivity. Damaged DNA is the site of signal generation; however, alternative signaling at the plasma membrane is triggered: Reactive oxygen species (ROS) inactivate phosphatases and consequently cause activation of kinases localized at the plasma membrane; this includes ligand-independent activation of receptor kinases. Cells with an apparently functional DNA repair system may show increased radiation sensitivity due to deficiencies in specific kinases essential for repair activation and checkpoint control. Other signals that determine intrinsic radiosensitivity may affect proneness to apoptosis, the balance between DNA damage fixation and repair, and the translocation of proteins participating in the response to ionizing radiation. Interplay between the various signals decides the extent to which the repair of radiation-inflicted damage is supported or limited; in some cell types, this includes DNA-damage-independent processes guided by plasma membrane-generated signaling. Cellular signaling in the context of specific subcellular structures is the key to understanding how the molecular effects of radiation are expressed as biological consequences in various cell types. A systems approach should bring us closer to this end.

Quantified relationship between cellular radiosensitivity, DNA repair defects and chromatin relaxation: a study of 19 human tumour cell lines from different origin

BACKGROUND AND PURPOSE

There is still confusion in the choice of the molecular assays to predict the radiation response of human cells. The case of tumours appears to be particularly complex, may be because of their instability and heterogeneity. The aim of this study was to investigate quantitatively the relationships between DNA double-strand breaks (DSB) repair, chromatin relaxation and cellular radiosensitivity. Nineteen human tumour cell lines, representing a large spectrum of radiation responses and tissues, were examined.

MATERIALS AND METHODS

Intrinsic radiosensitivity was quantified with surviving fraction at 2 Gy (SF2) as an endpoint. Standard and modified pulsed-field gel electrophoresis techniques were employed to assess DSB repair rate and chromatin relaxation. A cell-free assay was chosen to estimate DSB repair activity, independently of chromatin impairment.

RESULTS AND CONCLUSIONS

Surviving fraction at 2 Gy (SF2) decreases linearly with the amount of unrepaired DSB and the extent of chromatin relaxation: one additional unrepaired DSB per cell or 1% chromatin decondensation produce a loss of about 1.5% surviving fraction. However, all the cell lines did not obey both correlations, suggesting that DSB repair and chromatin impairments contribute separately to increase the severity of DNA damage involved in cell lethality. Four cell lines groups showing different DSB repair and/or chromatin impairments were defined. Cell lines exhibiting both DSB repair defect and chromatin relaxation are the most radiosensitive.

Measurements using the alkaline comet assay predict bladder cancer cell radiosensitivity

In the UK, the two main treatments of invasive bladder cancer are radiotherapy or cystectomy. However, ∼50% of patients undergoing radiotherapy fail to respond. If tumour radiosensitivity could be predicted in advance, it may be possible to improve control rates significantly by selecting for radiotherapy those patients whose tumours are radiosensitive. Additionally, patients who would benefit from surgery would be identified earlier. The alkaline comet assay (ACA) is a sensitive method for the detection of DNA strand break damage in cells. In the present study, using six bladder cancer cell lines of differing radiosensitivities, cell survival was compared to the manifestation of radiogenic DNA damage as assessed by ACA. For all the cell lines, the extent of comet formation strongly correlates with cell killing (R²>0.96), with a greater response being noted in radiosensitive cells. In repair studies, measures of residual damage correlate with survival fraction at 2 Gy (R²>0.96), but for only five of the cell lines. Finally, cells from human bladder tumour biopsies reveal a wide range of predicted radiosensitivies as determined by ACA. Overall, these studies demonstrate ACA to be a good predictive measure of bladder cancer cell radiosensitivity at low dose, with potential clinical application.

Potential use of the alkaline comet assay as a predictor of bladder tumour response to radiation

Bladder tumours show a variable response to radiotherapy with only about 50% showing good local control; currently there is no test to predict outcome prior to treatment. We have used five bladder tumour cell lines (T24, UM-UC-3, TCC-SUP, RT112, HT1376) to investigate the potential of the alkaline comet assay (ACA) to predict radiosensitivity. Radiation-induced DNA damage and repair were compared to clonogenic survival. When the five cell lines were irradiated and initial DNA damage was plotted against cell survival, at all doses (0-6 Gy), a significant correlation was found (r2=0.9514). Following 4 Gy X-irradiation, all cell lines, except T24, showed a correlation between SF2 vs half-time for repair and SF2 vs residual damage at 5, 10, 20 and 30 min. The T24 cell line showed radioresistance at low doses (0-2 Gy) and radiosensitivity at higher doses (4-6 Gy) using both cell survival and ACA end points, explaining the lack of correlation observed for this cell line. These data indicate that initial DNA damage and residual damage can be used to predict for radiosensitivity. Our data suggest that predictive tests of radiosensitivity, appropriate to the clinical situation, may require the use of test doses in the clinical range.

Evaluation of chromosome breakage and DNA integrity in sperm: an investigation of remote semen collection conditions

Collection of ejaculated semen at a remote site (outside of the laboratory) would facilitate participation rates and geographic diversity in reproductive epidemiology studies. Our study addressed concerns that remote collection and overnight mail return might induce chromosome/DNA damage. We collected semen from 10 healthy men. Part of each sample was snap frozen in liquid nitrogen and the rest held at 22 +/- 1 degrees C for 24 hours in a transport container (simulating ambient temperature during overnight return) then snap frozen. DNA breakage and fragmentation were measured using tandem-label sperm-fluorescence in situ hybridization (FISH), terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL), and neutral comet assay. Tandem-label sperm-FISH and TUNEL detected no statistically significant difference between sperm fresh frozen (FF) and those frozen after 24 hours (F24). The mean frequency of chromosome breakage per 10 000 cells scored in sperm-FISH for FF and F24 was 10.5 +/- 1.3 breaks and 11.2 +/- 1.1 breaks, respectively (P =.69, Student's t test). The mean frequency of TUNEL-positive cells per 2000 cells scored in FF and F24 was 136 +/- 29 and 213 +/- 28 cells, respectively, which approached but did not reach statistical significance (P = 0.07, Student's t test). The neutral comet assay detected a statistically significant difference in DNA strand breakage between the 2 groups (percentage of DNA in the tail P = 0.037; tail moment P = 0.006; and tail length P = 0.033, all Student's t test). The mean frequency of damage denoted by tail length in micro m per 100 cells scored in FF and F24 was 175.0 +/- 15.5 and 152.2 +/- 17.6 micro m, respectively. Tandem-label sperm-FISH, TUNEL, and neutral comet assay are useful analytical techniques for laboratory-based studies of human sperm genomic integrity; however, for field studies incorporating the nonrefrigerated return of semen after 24 hours, only chromosome breakage at a level that can be detected using tandem-label sperm-FISH was unaffected. TUNEL and neutral comet assay need further study before they are used in specimens collected at remote sites and transported to a central laboratory.

The relationship between cellular radiosensitivity and radiation-induced DNA damage measured by the comet assay

The relationship between deoxyribonucleic acid (DNA) damage and the cell death induced by gamma-irradiation was examined in three kinds of cells, Chinese hamster ovary fibroblast CHO-K1, human melanoma HMV-II and mouse leukemia L5178Y. Cell survival was determined by a clonogenic assay. The induction and rejoining of DNA strand breaks induced by radiation were measured by the alkaline and neutral comet assays. L5178Y cells were the most radiosensitive, while CHO-K1 cells and HMV-II cells were radioresistant. There was an inverse relationship between the survival fraction at 2 Gy (SF2) and the yield of initial DNA strand breaks per unit dose under the alkaline condition for the comet assay, and also a relationship between SF2 and the residual DNA strand breaks (for 4 hr after irradiation) under the neutral condition for the comet assay, the latter being generally considered to be relative to cellular radiosensitivity. In the present analysis, it was considered that the alkaline condition for the comet assay was optimal for evaluating the initial DNA strand breaks, while the neutral condition was optimal for evaluating the residual DNA strand breaks. Since the comet assay is simpler and more rapid than other methods for detecting radiation-induced DNA damage, this assay appears to be a useful predictive assay for evaluating cellular clonogenic radiosensitivity of tumor cells.

Does radiotherapy affect the outcome of the comet assay?

This study was designed to assess possible effects of fractionated radiotherapy (5 or 10 fractions at 2 Gy per fraction) on the DNA repair capacity of lymphocytes, as measured by the comet assay. 50 patients with various tumour types were chosen. They had received no chemotherapy during the 6 months prior to radiotherapy and did not receive cortisone. 10 ml of heparinized blood was collected before radiotherapy, after 5 fractions and after 10 fractions. Lymphocytes were isolated and analysed using the comet assay. On average, no effect on DNA repair capacity was observed that could be attributed to radiotherapy. On an individual basis, there were a few patients who showed a comparatively pronounced variability in their response to radiotherapy (three patients with a relative coefficient of variability of more than 30%). There was some indication of a weak correlation between poor repair capacity and severe side effects in normal tissue. We also found that alcohol in particular, and smoking to some extent, may impair repair capacity during radiotherapy. Age, gender, field size, medication and tumour entity showed no effect on repair capacity.

A modified neutral comet assay: elimination of lysis at high temperature and validation of the assay with anti-single-stranded DNA antibody

Comet assay under neutral conditions allows the detection of DNA double-strand breaks (DSB), considered to be the biologically relevant radiation-induced lesion. In this report, we describe modifications of the neutral comet method, which simplify and facilitate its use for estimation of DNA DSB in X-irradiated mammalian cells in culture. The analysis carried out according to this protocol takes less time than those most often applied. Also, the use of lysis at 50 degrees C is avoided; this is important in view of the presence of heat-labile sites in the chromatin of irradiated cells, recently reported by Rydberg [Radiation-induced heat-labile sites that convert into DNA double-strand breaks, Radiation Research 153 (2000) 805-812]. The comets have well-defined, sharp limits, suitable for image analysis. The chromatin of the hydrogen peroxide-treated or UV-C-irradiated cell remains condensed similarly to that of the control cells. We checked the neutral comets for the presence of single-stranded DNA by means of a specific antibody. The results point to a satisfactory sensitivity of the modified neutral comet assay and its specificity for DSB. The minimum detection level of the modified neutral comet assay is about 5 Gy.

Induction and rejoining of DNA double-strand breaks in bladder tumor cells

The induction and rejoining of radiation-induced double-strand breaks (DSBs) in cells of six bladder tumor cell lines (T24, UM-UC-3, TCC-SUP, RT112, J82, HT1376) were measured using the neutral comet assay. Radiation dose-response curves (0-60 Gy) showed damage (measured as mean tail moment) for five of the cell lines in the same rank order as cell survival (measured over 0-10 Gy), with the least damage in the most radioresistant cell line. Damage induction correlated well with clonogenic survival at high doses (SF10) for all six cell lines. At the clinically relevant dose of 2 Gy, correlation was good for four cell lines but poor for two (TCC-SUP and T24). The rejoining process had a fast and slow component for all cell lines. The rate of these two components of DNA repair did not correlate with cell survival. However, the time taken to reduce the amount of DNA damage to preirradiated control levels correlated positively with cell survival at 10 Gy but not 2 Gy; radioresistant cells rejoined the induced DSBs to preirradiation control levels more quickly than the radiosensitive cells. Although the results show good correlation between SF10 and DSBs for all six cell lines, the lack of correlation with SF2 for TCC-SUP and T24 cells would suggest that a predictive test should be carried out at the clinically relevant dose. At present the neutral comet assay cannot achieve this.

Fibroblast radiosensitivity measured using the comet DNA-damage assay correlates with clonogenic survival parameters

A study was made of the neutral comet assay as a potential method for measuring normal cell radiosensitivity. Eleven fibroblast strains were studied comprising nine derived from vaginal biopsies from pretreatment cervical cancer patients and two strains from radiosensitive individuals. DNA double strand break (dsbs) dose-response curves for both initial and residual (20-h repair time) damage were obtained over the dose range 0-240 Gy, with slopes varying 3.2 and 8-fold respectively. Clonogenic cell survival parameters were available for all the cell strains following both high- and low-dose rate irradiation. There were no correlations between the dose-response slope of the initial level of DNA dsbs and parameters that mainly describe the initial portion of clonogenic radiation survival curves (SF2, alpha, D). A significant correlation (r = -0.63, P = 0.04) was found between the extent of residual DNA dsbs and clonogenicity for all 11 fibroblast strains. The parameter showing the highest correlation with fibroblast cell killing (D) for the nine normal fibroblasts alone was the ratio of initial/residual DNA dsb dose-response slope (r = 0.80, P = < 0.01). A significant correlation (r = -0.67, P = 0.03) with clonogenic radiosensitivity was also found for all 11 cell strains when using the ratio of initial/residual DNA dsb damage at a single dose of 180 Gy. This study shows that fibroblast radiosensitivity measured using the neutral comet assay correlates with clonogenic radiation survival parameters, and therefore may have potential value in predictive testing of normal tissue radiosensitivity.

[Tumor and individual radiosensitivity. An introduction]

This text is intended to introduce the following articles, which correspond to the lectures given at the "Radiosensitivity" session of the 1998 SFRO Meeting. We first underline the somewhat disappointing results obtained so far for evaluating tumoral radiosensitivity. However, a few new tests could bring some hope in a not-too distant future. We then focus on individual radiosensitivity. We first list the syndromes or diseases associated with a known hyperradiosensitivity. We then concentrate on the radiosensitivity tests that are available in 1998, some of them being already used in a few centers in specific situations. However, the "optimal" test is still to be identified. After a brief chapter on the possible modulations of radiosensitivity, we conclude with a few recommendations to the clinician.