Immunophenotypic and gene expression analysis of monoclonal B-cell lymphocytosis shows biologic characteristics associated with good prognosis CLL.

Monoclonal B-cell lymphocytosis (MBL) is a hematologic condition wherein small B-cell clones can be detected in the blood of asymptomatic individuals. Most MBL have an immunophenotype similar to chronic lymphocytic leukemia (CLL), and 'CLL-like' MBL is a precursor to CLL. We used flow cytometry to identify MBL from unaffected members of CLL kindreds. We identified 101 MBL cases from 622 study subjects; of these, 82 individuals with MBL were further characterized. In all, 91 unique MBL clones were detected: 73 CLL-like MBL (CD5(+)CD20(dim)sIg(dim)), 11 atypical MBL (CD5(+)CD20(+)sIg(+)) and 7 CD5(neg) MBL (CD5(neg)CD20(+)sIg(neg)). Extended immunophenotypic characterization of these MBL subtypes was performed, and significant differences in cell surface expression of CD23, CD49d, CD79b and FMC-7 were observed among the groups. Markers of risk in CLL such as CD38, ZAP70 and CD49d were infrequently expressed in CLL-like MBL, but were expressed in the majority of atypical MBL. Interphase cytogenetics was performed in 35 MBL cases, and del 13q14 was most common (22/30 CLL-like MBL cases). Gene expression analysis using oligonucleotide arrays was performed on seven CLL-like MBL, and showed activation of B-cell receptor associated pathways. Our findings underscore the diversity of MBL subtypes and further clarify the relationship between MBL and other lymphoproliferative disorders.

Baldness, acne and testicular germ cell tumours.

Androgen levels during critical periods of testicular development may be involved in the aetiology of testicular germ cell tumours (TGCT). We evaluated the roles of adolescent and early adult life correlates of androgen exposure and TGCT in a hospital-based case-control study. TGCT cases (n=187) and controls (n=148), matched on age, race and state of residence, participated in the study. Unconditional logistic regression was used to estimate associations between TGCT and male pattern baldness, severe acne, markers of puberty onset and body size. Cases were significantly less likely to report hair loss than controls [odds ratio (OR): 0.6; 95% confidence interval (CI): 0.4, 1.0]. Amount of hair loss, increasing age at onset and increasing rate of loss were all inversely associated with TGCT (rate of hair loss: p-trend=0.03; age at onset: p-trend=0.03; amount of hair loss: p-trend=0.01). History of severe acne was inversely associated with TGCT (OR: 0.5; 95% CI: 0.3, 0.9) and height was positively associated with TGCT (p-trend=0.02). Increased endogenous androgen levels during puberty and early adulthood may be associated with a decreased risk of TGCT. Additional studies of endogenous hormone levels during puberty and early adult life are warranted, especially studies evaluating the role of androgen synthesis, metabolism and uptake.

Survival of patients with multiple primary malignancies: a study of 783 patients with gastrointestinal stromal tumor.

BACKGROUND: We sought to investigate the characteristics and survival rate of patients with gastrointestinal stromal tumor (GIST) associated with other primary malignancies. PATIENTS AND METHODS: A total of 783 patients with GIST were identified from 1995 to 2007. Additional primaries included tumors not considered metastasis, invasion, or recurrence of GIST, nor non-melanoma skin cancer. Data on gender, age at diagnosis, follow-up time after diagnosis, and death were collected. RESULTS: Of the 783 patients with GIST, 153(20%) were identified with at least one additional primary. Patients with additional primaries were more often men (M : F 1.5 versus 1.3) and older (66 versus 53 years). More patients had another cancer diagnosed before (134) than after (52) GIST. Primaries observed before GIST were cancers of the prostate (25), breast (12), esophagus (9), and kidney (7) and melanoma (6). Lung (5) and kidney (5) primaries were the most frequent after GIST. The 5-year survival was 68% for patients with primaries before GIST, 61% for patients with primaries after GIST, 58% for patients with GIST only, and 49% for patients with two or more primaries in addition to GIST (P = 0.002). CONCLUSIONS: Approximately 20% of patients with GIST develop other cancers. Inferior median 5-year survival was observed in patients with GIST with two or more other cancers. The etiology and clinical implications of other malignancies in patients with GIST should be investigated.

Risk factors of myelodysplastic syndromes: a case-control study.

Little is known about the etiology of myelodysplastic syndromes (MDS). A hospital-based case-control study of 354 adult de novo MDS cases and 452 controls was conducted to investigate associations between lifestyle characteristics and MDS risk. The distribution by French-American-British (FAB) type was 67 (19%) refractory anemia (RA), 38 (11%) refractory anemia with ringed sideroblasts (RARS), 43 (12%) chronic myelomonocytic leukemia (CMML), 136 (38%) RA with excess blasts (RAEB), and 70 (20%) RAEB in transformation (RAEBT). Multivariate logistic regression analyses were performed among all MDS cases and among each FAB type and gender. For all MDS combined, family history of hematopoietic cancer (odds ratio (OR) = 1.92), smoking (OR = 1.65), and exposure to agricultural chemicals (OR = 4.55) or solvents (OR = 2.05) were associated with MDS risk. Among RA/RARS cases, smoking (OR = 2.23) and agricultural chemical exposure (OR = 5.68) were the only risk factors identified. For RAEB/RAEBT cases, family history of hematopoietic cancer (OR = 2.10), smoking (OR = 1.52), and exposure to agricultural chemicals (OR = 3.79) or solvents (OR = 2.71) were independent risk factors. Drinking wine reduced risk for all FAB types by almost 50% (OR = 0.54). We found a joint effect between smoking and chemical exposure with the highest risk among smokers exposed to solvents/agricultural chemicals (OR = 3.22). Results from this large study suggest that several factors play a role in MDS predisposition with possible joint effects. Risk profiles seem to differ by FAB type and gender.

Long-term follow-up of normal peripheral blood progenitor cell donors treated with filgrastim: no evidence of increased risk of leukemia development.

Data on the long-term safety of filgrastim administration in peripheral blood progenitor cell (PBPC) donors are scarce. The main theoretical risk is believed to be the possible development of leukemia. We conducted a survey of filgrastim-treated related donors to determine the incidence of leukemia after PBPC donation. Of the 343 PBPC donors eligible for inclusion in the survey, 281 (82%) were interviewed by telephone between December 1998 and February 2000. The mean age at donation was 44 years. The median time elapsed after PBPC donation was 39 months, and in 278 (99%) of the interviewed donors it was at least 1 year. At the time of the interview none of the donors had been diagnosed with acute or chronic leukemia. Although the sample size is small and the follow-up duration is limited, these data suggest that exposure to filgrastim is not associated with any notable risk of leukemia development in PBPC donors.

Genetic susceptibility to Hodgkin's lymphoma and to secondary cancer: workshop report.

Although the occurrence of familial Hodgkin's lymphoma (HL) is a rare event, genetic susceptibility as a cause of HL and its influence on treatment outcome may not be rare. However, results obtained from the analysis of HL families will probably have broad implications with regard to understanding common pathogenic factors leading to the development of the disease. The description of anticipation among the affected offspring of HL patients further strengthens the view that heritable factors contribute to development of HL. Moreover, the finding that particular human leukocyte antigen (HLA) alleles are associated with susceptibility to HL may be regarded as a hint to the presence of an as yet undefined infectious agent, leading to the growth of a malignant lymphoma cell clone in those patients that are more susceptible to this agent due to their HLA genotype. In addition, since an intrinsic genomic instability was observed in a proportion of HL patients, it is plausible that these patients are not only susceptible to the causation of HL, but are also at a higher risk of developing therapy-related (TR) secondary cancers following treatment. Estimation of sister chromatid exchange was established as a tool to identify patients at higher risk of TR cancer. In this context the use of therapeutic agents known to increase genomic instability should be carefully considered prior to determing the best treatment. The future identification of heritable factors contributing to HL will be of importance both with regard to diagnosis as well as treatment of HL patients.

Is there an increased rate of additional malignancies in patients with mantle cell lymphoma?

PURPOSE: To examine the frequency of additional neoplasms preceding and following the diagnosis of mantle cell lymphoma (MCL). PATIENTS AND METHODS: A total of 156 patients with MCL treated on the hyperfractionated cyclophosphamide, vincristine, doxorubicin and dexamethasone alternated with methotrexate and cytosine arabinoside (Hyper-CVAD/M-A) program with or without rituximab from 1994 to 2000 were the subjects of this report. RESULTS: These patients were followed for a median time of 26 months, and a total of 32 (21%) additional neoplasms were diagnosed, 21 preceding the diagnosis of MCL and 11 following MCL. After excluding certain types of non-invasive neoplasms, including basal cell carcinoma, meningioma and cervical intraepithelial neoplasia, we observed seven second malignancies after the diagnosis of MCL, and the 5-year cumulative incidence rate of second malignancy was 11%. The observed-to-expected (O/E) ratio was 7/0.07 = 100 [95% confidence interval (CI) 49.3 to 186.6; P <0.0001]. Of the 21 malignancies diagnosed prior to MCL, 16 were invasive and five non-invasive. There were a total of 10 urologic malignancies occurring before or after the diagnosis of MCL was established. CONCLUSIONS: Our findings suggest that there is an increased incidence of second malignancies in patients with MCL. In addition, the high number of cases with urinary tract cancer in our series may substantiate prior reports describing a possible association between lymphoma and urologic malignancies.

Polymorphic hCHK2/hCds1 codon 84 allele and risk of squamous cell carcinoma of the head and neck--a case-control analysis.

Checkpoint kinase 2 (hCHK2/hCds1) is a tumor suppressor gene involved in cell-cycle control. A hCHK2/hCds1 polymorphism in codon 84 (A-->G at nucleotide 252) was recently identified in Li-Fraumeni syndrome patients. Because cell cycle regulates DNA repair that is associated with cancer risk, we hypothesized that this new polymorphism exists in the general population and is associated with cancer risk. To test this hypothesis, we evaluated the role of this polymorphism in a case-control study of 215 non-Hispanic white patients with newly diagnosed squamous cell carcinoma of the head and neck (SCCHN) and 229 frequency-matched cancer-free controls. We found that the hCHK2/hCds1 codon 84 variant was rare and less frequent in non-Hispanic white cases (0.0186) than in controls (0.0437; P = 0.033). Although no variant homozygotes were detected in these cases and controls, heterozygosity protected against SCCHN, representing a 60% reduction of risk (adjusted odds ratio = 0.40; 95% confidence intervals, 0.17-0.93) compared with wild-type homozygotes. The variant allele was also rare in other ethnic groups (0.0487, 0.0095 and 0.0541 in 115 African Americans, 105 Hispanic Americans and 111 native Chinese, respectively), and only one variant homozygous individual (a Chinese subject) was identified. These results suggest that this hCHK2/hCds1 codon 84 polymorphism is rare and may have a protective role in the aetiology of SCCHN in non-Hispanic whites. Larger studies are warranted to confirm this finding and further mechanistic studies are needed to understand biological relevance of this polymorphism.

Chemoprevention of breast cancer with selective estrogen receptor modulators: views from broadly diverse focus groups of women with elevated risk for breast cancer.

Selective estrogen receptor modulators (SERMs) are anti-estrogens that selectively antagonize the proliferative effects of estrogens on breast cells, thereby inhibiting or reversing neoplastic progression to clinical breast cancer. The goal is to administer these agents to healthy women with an elevated risk for breast cancer. The study reported here assessed the knowledge and attitude of 26 broadly selected women with an elevated risk for breast cancer who participated in three focus groups (eight to ten per group) that discussed the use of SERMs, such as tamoxifen and raloxifen. Data were analyzed by cross-case procedure using variable-oriented strategies. Acceptance of breast cancer chemoprevention treatment with SERMs was found to be influenced by various factors, including a knowledge of breast cancer risk factors, the perception of personal risk for breast cancer, and the perception of barriers and benefits to receiving chemoprevention treatment. The issues involved in making the decision to accept treatment with SERMs are discussed. Most of the participants in the groups indicated they were unlikely to accept breast cancer chemoprevention treatment with SERMs.

Cyclin D1 polymorphism and risk for squamous cell carcinoma of the head and neck: a case-control study.

A G-->A polymorphism (G870A) in exon 4 of the cyclin D1 (CCND1) gene creates an alternative splice site in its mRNA, encoding a protein with an altered C-terminal domain. It has been suggested that DNA damage in cells with the A allele bypasses the G(1)/S checkpoint of the cell cycle more easily than damage in cells without the A allele. Because CCND1 plays a critical role in cell cycle control and reduced DNA repair capacity is associated with an increased risk for squamous cell carcinoma of the head and neck (SCCHN), we hypothesize that this CCND1 polymorphism modulates individual susceptibility to SCCHN. To test this hypothesis we evaluated the frequency of the polymorphism in a hospital-based case-control study of 233 newly diagnosed SCCHN patients and 248 non-cancer controls. The cases and controls were frequency matched by age (+/-5 years), sex and tobacco use. All subjects were non-Hispanic whites. We found that the A allele frequency was slightly higher in the cases (0.485) than in the controls (0.425), but the difference was borderline statistically significant (P = 0.064). The frequencies of the CCND1 AA, GA and GG genotypes were 23.6, 49.8 and 26.6%, respectively, in cases and 16.5, 52.5 and 31.5%, respectively, in controls. Multivariate logistic regression analysis adjusting for age (in years), sex, smoking and alcohol use was performed to calculate odds ratios (OR) and 95% confidence intervals (CI). Compared with the wild-type CCND1 GG, the CCND1 A G genotype was associated with a non-significantly increased risk (adjusted OR 1.15, 95% CI 0.75-1.76), but the CCND1 AA genotype was associated with a significantly increased risk (adjusted OR 1.77, 95% CI 1.04-3.02) for SCCHN. Results from a trend test using a logistic regression model were statistically significant (P = 0.044). Among the cases the mean age of onset was 59.0, 56.8 and 55.5 years for the GG, GA and AA genotypes, respectively. In the stratification analysis the CCND1 AA variant genotype was associated with a >3-fold increased risk in individuals who were

Limiting the location of putative human prostate cancer tumor suppressor genes on chromosome 18q.

We studied loss of heterozygosity (LOH) on the long arm of human chromosome 18 in prostate cancer to determine the location of a putative tumor suppressor gene (TSG) and to correlate these losses with the pathological grade and stage of the cancer. Of 48 specimens analysed 17 (35.4%) lost at least one allele on chromosome 18q. All the specimens with allelic losses lost at least one allele within chromosomal region 18q21. Allelic losses picked at D18S51 (19%) and D18S858 (17%). A 0.58 cM DNA segment that includes the D18S858 locus and is flanked by the microsatellite loci D18S41 and D18S381, was lost in eight (47%) of 17 specimens with allelic losses. This segment was designated as a LOH cluster region 1 (LCR 1). Although Smad2 resides within LCR 1, it was not mutated in any of the six prostate cell lines (five prostate cancer cell lines and one immortalized prostate epithelial cell line) analysed, suggesting that it is not a candidate TSG in prostate cancer. A second LCR at 18q21, LCR 2, includes the D18S51 locus and is flanked by the D18S1109 and D18S68 loci, which are separated by 7.64 cM. LCR 2 was lost in six (35%) of the 17 specimens with chromosome 18q losses. These results suggest that chromosome 18q21 may harbor two candidate prostate cancer TSGs. The candidate TSGs DCC and Smad4 are located centromeric to the LCRs. No alleles were lost within or in close proximity to these genes, suggesting that they are not targets for inactivation by allelic losses in prostate cancer. Although there was no obvious correlation between chromosome 18q LOH and the pathological grade or stage, three (37.5%) of eight low-grade cancers and nine (32.1%) of 28 organ-confined cancers lost alleles at 18q21, suggesting that allelic losses are relatively early events in the development of invasive prostate cancer.

Reduced expression of hMSH2 and hMLH1 and risk of prostate cancer: a case-control study.

BACKGROUND: Although prostate cancer is the most common incident cancer in men, not much is known about its etiology. We tested the hypothesis that expression levels of hMSH2 and hMLH1 in unaffected (normal) tissue play a role in the etiology of prostate cancer. METHODS: Total RNA was extracted from peripheral blood lymphocytes of subjects ascertained by a case-control study (70 patients and 97 age- and ethnicity-matched controls). A multiplex reverse transcription-polymerase chain reaction assay was used to simultaneously evaluate the relative expression of hMSH2 and hMLH1, using beta-actin as the internal control. RESULTS: The relative gene expression levels of hMSH2 and hMLH1 were significantly lower in cases than in controls (P < 0.05 for both genes). When compared with the highest tertile of the controls, low expression levels (the middle and lowest tertiles) of hMLH1 were associated with significantly increased risk of prostate cancer in a dose-response relationship (ORs = 2.68, and 4.31; 95% confidence interval = 1.00-7.23 and 1.64-11.30, respectively) after adjustment for age, ethnicity, smoking status, and family history of prostate cancer. CONCLUSIONS: These results suggest that reduced expression of hMLH1 in peripheral lymphocytes may be a risk factor for prostate cancer. However, it cannot be ruled out that the reduced expression we observed may be caused by the disease status. Our findings and the factors that may affect the expression of hMLH1 need further confirmation in larger prospective studies.

An intronic poly (AT) polymorphism of the DNA repair gene XPC and risk of squamous cell carcinoma of the head and neck: a case-control study.

Inherited polymorphisms of DNA repair genes may contribute to variations in DNA repair capacity and genetic susceptibility to cancer. In a hospital-based case-control study of 287 non-Hispanic white patients with newly diagnosed SCCHN and 311 control subjects matched on age, sex, ethnicity, and smoking status, we investigated the role of a newly identified variant allele of XPC, XPC-PAT+. We found that the frequency of the XPC-PAT+ allele was higher in the cases (0.409) than in the controls (0.333; P = 0.007). Fifty cases (17.4%) and 37 controls (11.9%) were XPC-PAT+/+, and 135 (47.0%) cases and 133 controls (42.8%) were XPC-PAT+/-. XPC-PAT+/- and XPC-PAT+/+ subjects were at significantly increased risk for SCCHN [adjusted odds ratios = 1.44 and 1.85, respectively (95% confidence intervals, 1.01-2.05 and 1.12-3.05, respectively; trend test, P = 0.007)]. We did not find ethnic difference in the frequency of XPC-PAT+ allele among four groups aged between 19 and 75 years: non-Hispanic whites, 294; African-Americans, 178; Hispanic-Americans, 103; and native Chinese, 119 (0.333, 0.281, 0.296, and 0.353, respectively). The case-control findings support the hypothesis that the XPC-PAT+ allele may contribute to the risk of developing SCCHN.

Alcohol dehydrogenase 3 genotype is not associated with risk of squamous cell carcinoma of the oral cavity and pharynx.

Alcohol is one of the major risk factors for oral and pharyngeal cancer. The rate-limiting step in alcohol metabolism is the oxidation (activation) of ethanol to acetaldehyde by the alcohol dehydrogenases (ADHs). It has been hypothesized that individuals who are homozygous for the fast allele (ADH(1-1)(3)) are at greater risk for alcohol-related cancers. To test this hypothesis, we investigated the association between the ADH3 genotype and oral and pharyngeal cancer risk in a large racially homogeneous case-control study of 229 patients and 575 matched control subjects with frequency matching on age, sex, and smoking status. Although the smoking status was matched between cases and controls, current and former alcohol use remained a significant risk factor, compared with never use (odds ratio, 2.08; 95% confidence interval, 1.37-3.17; odds ratio, 1.97; 95% confidence interval, 1.25-3.09; and odds ratio, 1.00, respectively). The ADH1(3) allele frequency of controls was 57.4%, consistent with reports of similar racial groups (50-60%). The genotype distribution in controls was also consistent with the Hardy-Weinberg equilibrium (P = 0.51). However, the ADH1(3) allele frequency and ADH(1-1)(3) genotype frequency were not significantly different between cases and controls [55.5% versus 57.4% (P = 0.52), and 30.6% versus 31.3% (P = 0.91), respectively]. There was no association between ADH3 genotypes (ADH(1-1)(3), ADH(1-2)(3), and ADH(2-2)(3)) and risk of oral and pharyngeal cancer (odds ratios, 1.00; 0.96; 95% confidence interval, 0.68-1.37; and odds ratio, 1.23; confidence interval, 0.78-1.93, respectively). Therefore, we found no evidence that supports a main effect of ADH3 genotype or a combined effect of alcohol and ADH3 genotype on risk of cancer of the oral cavity or pharynx.

Leptin and prostate cancer.

BACKGROUND: Higher prostate cancer mortality rates among US immigrants from countries with lower rates suggest environmental influences on prostate carcinogenesis (e.g., diet, body composition). METHODS: In a study identifying determinants of clinically relevant prostate cancer, we compared plasma concentrations of leptin, an adiposity-related hormone, in 48 men with tumors 0.5 cc in volume or with histologic evidence of extraprostatic extension but without metastases ("high-volume disease"), matched by age (+/- 5 years) and year at diagnosis (+/- 1 year). RESULTS: Men with high-volume disease exhibited higher leptin concentrations overall and after stratification by age, testosterone level, height, and body mass index (BMI). Analysis revealed that men with elevated leptin concentrations had an increased risk of diagnosis with high-volume disease (odds ratio (OR) = 2.35, 95% confidence interval (CI) = 1.01-5.44), as did men with high leptin and high testosterone (OR = 9.73, 95% CI = 2.05-46.24) and men >/=5'8" with high leptin (OR = 3.67, 95% CI = 1.40-9.63). CONCLUSIONS: Leptin may affect the risk of clinically relevant prostate cancer through testosterone and factors related to stature and obesity.

Statistical models for analysis of cytogenetic biomarkers.

BACKGROUND: Bleomycin-induced chromosomal breaks (CB) and sister chromatid exchange (SCE) in peripheral blood lymphocytes have been shown to be sensitive cytological markers for susceptibility to DNA damage in patients with various types of cancer and in healthy controls. Factors such as age, sex, smoking, and alcohol consumption could affect the values of some of these biomarkers and should be considered as covariates when analyzing cytogenetic biomarkers because these factors can affect the frequency of CB and SCE. METHODS: We propose a statistical method using negative binomial (NB) distribution to evaluate the numbers of CB and SCE. In order to determine the best model to represent the frequency of CB and SCE, we compared the NB model with the widely used Poisson model and log-transformed normal model by using generalized linear models. To demonstrate the better fit of the NB model, we analyzed three different data sets from studies conducted at The University of Texas M.D. Anderson Cancer Center. The first set was a case-control study of lung cancer in a population of African Americans and Mexican Americans (286 cases and 156 controls), the second set consisted of 311 head and neck cancer patients, and the third set consisted of 105 Hodgkin's disease patients. RESULTS: For CB; the estimates of the variability for Hodgkin's disease, head and neck, and lung cancers were 487.24, 502.82, and 520.15, respectively. For SCE, the estimates of the variability for Hodgkin's disease was 9777.01. For CB, the dispersion estimates under the three models (Poisson, NB, and Normal) for Hodgkin's disease, head and neck, and lung cancers were: 12.30, 1.20, 0.85; 8.94, 1.05, 0.22; and 10.10, 1.05, 0.25, respectively. For SCE (Hodgkin's disease only), the dispersion estimates under the three models (Poisson, NB, and Normal) were 30.91, 1.11, 0.10, respectively. CONCLUSIONS: Our results demonstrate that the NB model provides a better interpretation and fit for the frequency of CB and SCE in different cancer types. Therefore, we recommend it as a model for the analysis of cytogenetic biomarkers.

Epidemiologic determinants of clinically relevant prostate cancer.

While tumor volume and Gleason scores are the best available prognostic indicators for prostate cancer, contemporary predictive methods are unable to identify which men with Gleason scores of 7 have clinically insignificant tumors that will not progress and which men will develop highly aggressive prostate cancer. Our objective was to evaluate potential environmental determinants of significant prostate cancer. Subjects were patients identified from a university-based hospital and tertiary cancer center who had undergone radical prostatectomy for prostate cancer. Cases were 103 patients whose tumor volumes were

Gender difference in smoking effect on chromosome sensitivity to gamma radiation in a healthy population.

In the general population, there is variation in radiosensitivity associated with cancer risk. However, data on the role of epigenetic factors in the variation of radiosensitivity are scarce. Thus we investigated the effects of smoking and age on the radiosensitivity of human lymphocytes by measuring the frequency of chromosome aberrations after in vitro exposure to gamma rays in peripheral lymphocytes from 441 healthy subjects (18-95 years old). We analyzed the frequency of both spontaneous (baseline) and in vitro gamma-ray-induced (1.5 Gy) chromatid breaks in 50 well-spread metaphases per subject. The overall mean frequencies of spontaneous and induced breaks were 0.02 and 0.45 per cell, respectively. The mean frequency of induced breaks was significantly higher in men than in women (P = 0.03) but did not differ by age or ethnicity. Donors who had ever smoked showed a small but significantly increased frequency of induced breaks (mean = 0.47) compared to nonsmokers (mean = 0.41; P = 0.005). Further stratification and multivariate analyses revealed that the smoking effect was more pronounced in men than in women. These findings support a smoking effect on radiosensitivity in a healthy population, particularly in men. Therefore, when evaluating the association between radiosensitivity and susceptibility to smoking-related cancers, the effect of smoking should be taken into account.