Human endogenous retroviruses and their implication for immunotherapeutics of cancer.

Human endogenous retroviruses (HERVs) have recently caught increased attention as a potential internal trigger to sensitize tumor cells to immunotherapies. HERVs are remnants of retroviral germline infections that resulted in chromosomal integration into all the cells of the progeny. Today, HERVs constitute ∼8% of the human genome, but most elements are highly degenerated, under strict epigenetic regulation, and rarely expressed in healthy tissues. However, cancer cells are specifically prone to reactivate the expression of HERV elements due to epigenetic dysregulation that accumulate during malignant transformation and when using epigenetic therapies. HERV expression can induce an interferon response due to induction of the viral defense pathway, so-called 'viral mimicry'. By mimicking viral infections, HERVs could function as an 'intrinsic adjuvant', possibly sensitizing cancer cells to immunological recognition. Furthermore, translated HERV elements may in themselves form a valuable pool of tumor-associated antigens. Epitopes derived from HERVs have been recognized by cytotoxic CD8+ T cells, leading to cancer cell recognition. The combination of 'viral mimicry' and T-cell recognition could provide a powerful combination with existing immune stimulatory therapies, such as checkpoint inhibition. This combination is currently being evaluated in clinical trials in a large number of cancers.

Hepatocellular carcinoma in patients with chronic hepatitis C and cirrhosis in Denmark: A nationwide cohort study.

Cirrhosis in patients with chronic hepatitis C increases the risk of hepatocellular carcinoma (HCC), and surveillance with ultrasound (US) and alpha-fetoprotein (AFP) is recommended. This study aimed to estimate changes in the HCC incidence rate (IR) over time, HCC stage and prognosis, and AFP and US performed in patients with hepatitis C and cirrhosis. Eligible patients were identified in the Danish Database for Hepatitis B and C, and data from national health registries and patient charts were obtained. Tumour stage was based on Barcelona-Clinic Liver Cancer stage, TNM classification and size and number of lesions combined into stages 0-3. We included 1075 patients with hepatitis C and cirrhosis, free of HCC and liver transplant at baseline. During 4988 person years (PY), 115 HCC cases were diagnosed. The HCC incidence rate increased from 0.8/100 PY [CI95% 0.4-1.5] in 2002-2003 to 2.9/100 PY [2.4-3.4] in 2012-2013. One-year cumulative incidence of at least one AFP or US was 53% among all patients. The positive predictive value of an AFP ≥ 20 ng mL-1 was 17%. Twenty-three (21%) patients were diagnosed with early-stage HCC (stage 0/1) and 84 (79%) with late stage. Median survival after HCC for early-stage HCC disease was 30.1 months and 7.4 months for advanced HCC (stage 2/3). The incidence rate of HCC increased over time among patients with hepatitis C and cirrhosis in Denmark. Application of AFP and US was suboptimal, and most patients were diagnosed with advanced HCC with a poor prognosis.

The role of epigenetics in the biology of multiple myeloma.

Several recent studies have highlighted the biological complexity of multiple myeloma (MM) that arises as a result of several disrupted cancer pathways. Apart from the central role of genetic abnormalities, epigenetic aberrations have also been shown to be important players in the development of MM, and a lot of research during the past decades has focused on the ways DNA methylation, histone modifications and noncoding RNAs contribute to the pathobiology of MM. This has led to, apart from better understanding of the disease biology, the development of epigenetic drugs, such as histone deacetylase inhibitors that are already used in clinical trials in MM with promising results. This review will present the role of epigenetic abnormalities in MM and how these can affect specific pathways, and focus on the potential of novel 'epidrugs' as future treatment modalities for MM.

5-Azacytidine treatment sensitizes tumor cells to T-cell mediated cytotoxicity and modulates NK cells in patients with myeloid malignancies.

Treatment with the demethylating agent 5-Azacytidine leads to prolonged survival for patients with myelodysplastic syndrome, and the demethylation induces upregulation of cancer-testis antigens. Cancer-testis antigens are well-known targets for immune recognition in cancer, and the immune system may have a role in this treatment regimen. We show here that 5-Azacytidine treatment leads to increased T-cell recognition of tumor cells. T-cell responses against a large panel of cancer-testis antigens were detected before treatment, and these responses were further induced upon initiation of treatment. These characteristics point to an ideal combination of 5-Azacytidine and immune therapy to preferentially boost T-cell responses against cancer-testis antigens. To initiate such combination therapy, essential knowledge is required about the general immune modulatory effect of 5-Azacytidine. We therefore examined potential treatment effects on both immune stimulatory (CD8 and CD4 T cells and Natural Killer (NK) cells) and immune inhibitory cell subsets (myeloid-derived suppressor cells and regulatory T cells). We observed a minor decrease and modulation of NK cells, but for all other populations no effects could be detected. Together, these data support a strategy for combining 5-Azacytidine treatment with immune therapy for potential clinical benefit.

Limited clinical efficacy of azacitidine in transfusion-dependent, growth factor-resistant, low- and Int-1-risk MDS: Results from the nordic NMDSG08A phase II trial.

This prospective phase II study evaluated the efficacy of azacitidine (Aza)+erythropoietin (Epo) in transfusion-dependent patients with lower-risk myelodysplastic syndrome (MDS). Patients ineligible for or refractory to full-dose Epo+granulocyte colony stimulation factors for >8 weeks and a transfusion need of 4 units over 8 weeks were included. Aza 75 mg m(-2) d(-1), 5/28 days, was given for six cycles; non-responding patients received another three cycles combined with Epo 60 000 units per week. Primary end point was transfusion independence (TI). All patients underwent targeted mutational screen for 42 candidate genes. Thirty enrolled patients received one cycle of Aza. Ten patients discontinued the study early, 7 due to adverse events including 2 deaths. Thirty-eight serious adverse events were reported, the most common being infection. Five patients achieved TI after six cycles and one after Aza+Epo, giving a total response rate of 20%. Mutational screening revealed a high frequency of recurrent mutations. Although no single mutation predicted for response, SF3A1 (n=3) and DNMT3A (n=4) were only observed in non-responders. We conclude that Aza can induce TI in severely anemic MDS patients, but efficacy is limited, toxicity substantial and most responses of short duration. This treatment cannot be generally recommended in lower-risk MDS. Mutational screening revealed a high frequency of mutations.

Randomized controlled azathioprine withdrawal after more than two years treatment in Crohn's disease: increased relapse rate the following year.

INTRODUCTION: Azathioprine is effective for maintenance of remission in Crohn's disease, however, duration of efficacy and the dose response relationship has not been fully evaluated. AIMS: To investigate whether patients kept in remission by azathioprine treatment for >2 years benefit from further treatment, and to explore dose-response relationship. PATIENTS AND METHODS: In an open 12-month trial, patients with inactive Crohn's disease after >2 years (median 37 months) of azathioprine treatment were randomized to azathioprine withdrawal or continued treatment. Primary end point was relapse defined as: (i) Crohn's disease activity index rise >/= 75, and Crohn's disease activity index >150 or (ii) disease activity requiring intervention. RESULTS: Of 29 patients, 28 completed the observation period or relapsed. Eleven of 13 patients (85%) continuing azathioprine remained in remission compared with seven of 15 (47%) observed without azathioprine (P = 0.043). In patients who had been treated with azathioprine >1.60 mg/kg/day the difference was even more pronounced, eight of nine (89%) vs. four of 12 (33%) respectively (P = 0.017). CONCLUSIONS: Patients with Crohn's disease in remission after >2 years of continuous azathioprine treatment will benefit from further continued treatment. Further controlled studies with azathioprine doses <2.0 mg/kg/day are needed.

Interobserver variation in interpretation of serial liver biopsies from patients with chronic hepatitis C.

Reliable and accurate assessment of liver histopathology in patients with chronic hepatitis C is important for decision regarding treatment and for evaluation of therapy. However, little data on interobserver variation have been published. In this study, five specialist histopathologists evaluated 46 liver biopsies from 20 patients treated with interferon-alpha. Knodell's and Ishak's scoring systems, De Groote's classification and a four level general necro-inflammatory activity score (GNAS) were applied. Besides kappa statistics, slide by slide analysis was performed. We defined an acceptable slide by slide agreement as eight of ten observer pairs agreed on 80% of the slides. The best agreement was seen for Knodell's and Ishak's fibrosis score, De Groote's classification and GNAS (mean weighted kappa (kappa(w)) = 0.49, 0.51, 0.50 and 0.44, respectively). By condensing data from Knodell's and Ishak's scores to presence or absence of cirrhosis and piecemeal necrosis respectively, concordance was substantial concerning cirrhosis (mean kappa = 0.69 and 0.72, respectively) but only moderate concerning piecemeal necrosis (mean kappa = 0.40 and 0.39, respectively). Slide by slide analysis showed the highest agreement on Knodell's fibrosis score and GNAS; only one point of difference in score was to be accepted to obtain 'eight of ten' agreement. In contrast, five points of difference were necessary to accept in order to reach the same agreement for Knodell's total activity score. Moreover, in serial biopsies the GNAS was sufficient to detect changes in disease activity following treatment. Thus, a simple scoring system with four category scales was reproducible and sufficient for detection of therapy induced changes.

Interferon alfa-2b alone or combined with recombinant granulocyte-macrophage colony-stimulating factor as treatment of chronic hepatitis C.

BACKGROUND: To compare the effect of combination therapy with interferon-alpha (INF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) to monotherapy with INF-alpha in patients with chronic hepatitis C infection. METHODS: Forty-five consecutive patients with chronic hepatitis C, all presenting with elevated serum alanine aminotransferases and viremia, were randomized to receive either 1) INF-alpha + GM-CSF for 3 months followed by INF-alpha alone for 9 months (n = 23) or 2) INF-alpha for 12 months (n = 22). Both drugs were administered 3 times weekly in doses of 3 mU (INF-alpha) and 50-100 microg depending on body weight (GM-CSF). RESULTS: At baseline, there was no difference between the treatment groups in terms of age, sex, ALT level, viral load, genotype or histological activity and fibrosis in a pretreatment liver biopsy. After 12 months' treatment, more patients treated with GM-CSF+ INF-alpha compared to patients receiving monotherapy had normalized ALT, 65% and 32%, respectively (P = 0.03), but there was no difference in percentages of patients with viral clearance between the 2 groups, 48% and 32%, respectively (P = 0.27). At 6 months' follow-up, the biochemical response had declined to 35% in the combination therapy group and to 23% in the monotherapy group (P = 0.37); viral clearance had declined to 22% and 27%, respectively (P = 0.67), and the overall sustained response rate was 22% and 23%, respectively (P = 1.00). CONCLUSIONS: Even though patients receiving INF-alpha + GM-CSF had a significant better biochemical response during treatment compared to patients receiving monotherapy, the sustained biochemical and virological response was not increased. Thus, GM-CSF hardly plays any role in the future treatment of chronic hepatitis C.

A case of lymphoblastoid natural killer (NK)-cell lymphoma: association with the NK-cell receptor complex CD94/NKG2 and TP53 intragenic deletion.

The clinical, histological, phenotypic and genotypic features of a lymphoblastoid natural killer (NK)-cell lymphoma presenting in the skin in a young caucasian woman are described. The disease behaved aggressively, but long-lasting remission was obtained by combination chemotherapy followed by autologous bone marrow transplantation. The blastoid cells were positive for terminal deoxynucleotidyl transferase, CD34, CD56 and CD4. Furthermore, the NK-cell receptor complex CD94/NKG2 was strongly expressed, as shown by examination with reverse transcription-polymerase chain reaction. The T-cell receptor (TCR)-gamma genes were in germline, and with the exception of CD4 all T-cell antigens were negative, including CD3, TCR-beta, TCR-delta, TIA-1, granzyme B and perforin. Epstein-Barr virus was negative, and no expression was seen of myeloid cell-associated markers. Molecular analysis showed no abnormalities of the CDKN2A (p16), CDKN2B (p15) or TNFRSF6 (Fas) genes. By contrast, a 34-bp deletion in exon 7 of the TP53 (p53) gene was detected. It is suggested that lymphoblastoid NK-cell lymphoma, which is a rare but distinctive disease, originates from NK cell precursors and may be associated with and possibly caused by alterations in the TP53 gene. Experience is too limited to warrant therapeutic suggestions. However, stem cell transplantation may be a useful option in younger patients.

Concurrent disruption of p16INK4a and the ARF-p53 pathway predicts poor prognosis in aggressive non-Hodgkin's lymphoma.

The INK4a/ARF locus at chromosome 9p21 encodes two structurally and functionally distinct molecules with tumor-suppressive properties. p16INK4a controls cell cycle progression by inhibiting phosphorylation of the retinoblastoma protein (Rb), while ARF prevents MDM2-mediated degradation of p53. By using a panel of PCR-based methods, we have examined the status of the p16INK4a, ARF and p53 genes in 123 cases of non-Hodgkin's lymphoma (NHL) at diagnosis. Alterations of one or more of these genes were detected in seven of 36 (19%) cases with low- to intermediate-grade histology, and in 35 of 87 (40%) cases with aggressive histology. For the aggressive lymphomas, the Kaplan-Meier estimate of overall survival for cases with disruption of either p16INK4a or the ARF-p53 pathway was not different from cases with retention of both pathways (5 year survival 45% vs 35%; P= 0.85), suggesting that selective inactivation of one of the pathways does not significantly influence overall survival. By contrast, the 5-year survival was only 7% for cases with concurrent disruption of p16INK4a and the ARF-p53 pathway vs 38% for cases with retention of one or both pathways (P = 0.005). Similar results were obtained when the analysis was confined to diffuse large B cell lymphomas (P= 0.019). On stepwise multivariate regression analysis including factors from the international prognostic index, concurrent disruption of p16INK4a and the ARF-p53 pathway was an independent negative prognostic factor in NHL with aggressive histology (P = 0.006). Our results suggest that the compound status of the p16INK4a and ARF-p53 pathways is a major determinant of outcome in NHL.

Mutational analysis of the tumour suppressor gene MMAC1/PTEN in malignant myeloid disorders.

The candidate tumour suppressor gene MMAC1/PTEN located at chromosome 10q23.3 has been reported to be frequently mutated in a number of solid tumours. Less is known about its status in leukaemia. In the present study we first analysed 13 leukaemia cell lines for mutations and homozygous deletions in MMAC1/PTEN using PCR and denaturing gradient gel electrophoresis (DGGE). We identified an intragenic deletion including MMAC1/PTEN exons 2-5 in an acute myelocytic leukaemia cell line, HL-60 blast, and an insertion of four nucleotides in exon 5 in an acute monocytic leukaemia cell line, U937. Analysis of 59 patients with acute myeloid leukaemia (AML), 26 patients with myelodysplastic syndromes (MDS) and 10 patients with chronic myeloid leukaemia (CML) only revealed a polymorphic base substitution in codon 44 in one AML patient, suggesting that mutations in the MMAC1/PTEN gene are infrequent genetic aberrations in myeloid leukaemia.

[Transfusion-related hepatitis C. The Danish "look back" survey]. / Transfusionsoverført hepatitis C. Den danske "lookback"-undersøgelse. Den Danske HCV lookback gruppe.

This study accumulated results of the HCV lookback in Denmark and described the morbidity of the infected recipients. Donor records were identified for at least ten years back, and recipients still alive were tested for hepatitis C. Those with positive results were referred for clinical evaluation. A total of 150 Danish anti-HCV positive donors had donated blood to 1018 recipients of whom 288 (29%) were still alive. Because of age, malignancy or other severe diseases 118 (41%) of these were not contacted. Of 157 recipients screened for HCV, 128 (82%) were anti-HCV positive and 88 (56%) were HCV-RNA positive. Among the HCV-RNA positive recipients symptoms were present in 38% (25/66 reported), elevated ALT was found in 53% (41/77 tested) and cirrhosis was found in 11% (6/54 biopsied). Treatment with interferon-alpha was initiated in 23 patients, corresponding to 26% of HCV-RNA positive recipients.

Primary cutaneous B-cell lymphoma: a clinical, histological, phenotypic and genotypic study of 21 cases.

The clinical, histological, phenotypic and genotypic features of 21 primary cutaneous B-cell lymphomas (CBCLs) have been investigated. The patients were 13 men and eight women aged 34-91 years (median 67) at diagnosis. Eighteen patients had localized disease, and three had multiple skin lesions at diagnosis. Twelve patients developed cutaneous or extracutaneous recurrences, and five died from malignant lymphoma 7-84 months (median 36) after diagnosis. Histological examination showed features of marginal zone/mucosa-associated lymphoid tissue (MALT)-type lymphoma in 12 cases. Three of these had transformed to diffuse large B-cell lymphoma (DLBCL) in relapse biopsies. The remaining cases were seven primary DLBCLs and two cases tentatively classified as follicle centre cell (FCC) lymphoma. The neoplastic B cells showed similar phenotypes and genotypes in most cases (CD20+, CD79+, CD5-, CD10-, cyclin D1-, bcl-2+, bcl-x-, bax-, t(14;18)-negative). p53 protein was expressed in five cases, and four harboured mis-sense or loss-of-function mutations in the p53 gene. Deletion or promoter region hypermethylation of the p16INK4a gene was detected in two patients with DLBCL. The level of retinoblastoma protein expression and the proliferative fraction were significantly higher in DLBCL (> 50%) than in MALT- or FCC-type lymphomas (< 10%). Features associated with an unfavourable prognosis were the presence of multiple skin lesions at diagnosis, transformation from MALT-type lymphoma to DLBCL, and possibly p16INK4a aberrations. It is concluded that most CBCLs are dissimilar from FCC lymphomas and seem to be more closely related to marginal zone/MALT-type lymphomas. It is also suggested that there are fundamental differences between DLBCL and other histological categories of CBCL, indicating that cutaneous DLBCL is a separate entity with an increased growth potential and genetic features similar to DLBCL originating in other anatomical sites.

Natural history and etiology of liver disease in patients with previous community-acquired acute non-A, non-B hepatitis. A follow-up study of 178 Danish patients consecutively enrolled in The Copenhagen Hepatitis Acuta Programme in the period 1969-1987.

BACKGROUND/AIMS: Consecutive patients originally diagnosed with acute non-A, non-B hepatitis were followed up to assess the long-term morbidity and mortality and to re-evaluate the etiology in surviving patients. METHODS: Follow-up was performed in 178 patients with acute non-A, non-B hepatitis enrolled in the Copenhagen Hepatitis Acuta Programme in the period 1969-1987. Mortality and morbidity were assessed using: i) death certificates and ii) diagnoses at discharge following all somatic admissions. All patients who were alive were offered a re-examination encompassing clinical, biochemical and virological evaluation. RESULTS: After a median of 23 years, 71 (40%) had died and seven (4%) were untraceable. Overall mortality and mortality due to cirrhosis and accidents, mainly intoxication with drugs, were significantly higher compared to those of an age- and sex-matched Danish population. Chronic hepatitis had been diagnosed in 19 (11%) and cirrhosis in 16 (9%). Of 100 patients who were alive, 57 accepted a re-examination. Anti-HCV was detected in 24 (42%) and 19 (33%) were HCV-RNA positive. Of the viremic patients, 11 (58%) had elevated P-ALT, but only three (16%) had already been diagnosed with HCV infection. A history of intravenous drug use was tantamount to anti-HCV positivity. CONCLUSIONS: Danish patients with community-acquired acute non-A, non-B hepatitis had an increased mortality due to liver cirrhosis during the first years after the acute infection. Alcohol was the etiological agent in several cases, but HCV infection may also have been present. However, the long-term HCV-related morbidity and mortality were low.

In situ T cell responses against melanoma comprise high numbers of locally expanded T cell clonotypes.

It is well established that melanoma cells express Ags that are recognized by autologous T cells in vitro. Tumor-infiltrating lymphocytes in situ comprise clonotypic T cells, suggesting that their expansion is driven by Ag stimulation. Still, little is known about the detailed characteristics of the in situ T cell response. In the present study, we scrutinized this response by analyzing multiple metastatic lesions for the presence of clonotypic T cells. This approach was chosen to distinguish whether the clonal T cell expansion occurs as a systemic or localized phenomenon. TCR clonotype mapping of six s.c. metastases from two patients revealed the presence of multiple (from 40 to >60) clonotypic T cells in all lesions. Clonotypic T cells were present in TCR beta-variable regions expressed both at high and low levels. Comparison of the T cell clonotypes present in different lesions from individual patients demonstrated that, in general, clonotypes were exclusively detected in a single lesion. Hence, anti-melanoma T cell responses are much more heterogeneous than previously anticipated and accommodate a predominance of strictly localized T cell clonotypes.

Somatic Fas mutations in non-Hodgkin's lymphoma: association with extranodal disease and autoimmunity.

Fas (APO-1/CD95) is a cell-surface receptor involved in cell death signaling. Germline mutations in the Fas gene have been associated with autoimmune lymphoproliferative syndrome, and somatic Fas mutations have been found in multiple myeloma. We have examined the entire coding region and all splice sites of the Fas gene in 150 cases of non-Hodgkin's lymphoma. Overall, mutations were identified in 16 of the tumors (11%). Missense mutations within the death domain of the receptor were associated with retention of the wild-type allele, indicating a dominant-negative mechanism, whereas missense mutations outside the death domain were associated with allelic loss. Fas mutations were identified in 3 (60%) MALT-type lymphomas, 9 (21%) diffuse large B-cell lymphomas, 2 (6%) follicle center cell lymphomas, 1 (50%) anaplastic large cell lymphoma, and 1 unusual case of B-cell chronic lymphocytic leukemia with a marked tropism for skin. Among the 16 patients with somatic Fas mutations, 15 showed extranodal disease at presentation, and 6 relapsed in extranodal areas. Ten of 13 evaluable patients showed features suggestive of autoreactive disease. Our data indicate that somatic disruption of Fas may play a role in the pathogenesis of some lymphomas, and suggest a link between Fas mutation, cancer and autoimmunity.

Concurrent disruption of cell cycle associated genes in mantle cell lymphoma: a genotypic and phenotypic study of cyclin D1, p16, p15, p53 and pRb.

Mantle cell lymphomas (MCL) are morphologically and immunophenotypically distinctive lymphoid neoplasms characterised by overexpression of cyclin D1. Recent studies have suggested that co-operating aberrations of cell cycle associated genes may provide a growth advantage to a tumour. To address this issue further, we investigated five typical and three aggressive (blastoid) MCL for alterations in the cell cycle regulating genes p15, p16, CDK4, Rb and p53. In 3/3 aggressive cases with cyclin D1 overexpression we found aberration of at least one additional gene. One case showed diminished expression of the retinoblastoma protein (pRb); one case harboured deletion of both p15 and p16; and one case exhibited both deletion of p16 and point mutation of p53. However, we also identified two typical cases which in addition to cyclin D1 overexpression exhibited diminished pRb expression and p15 and p16 hypermethylation, respectively. Our findings confirm and extend other recent investigations and indicate that co-operating genetic alterations of cell cycle-associated genes may contribute to the pathogenesis of MCL.

Effect of smoking cessation on oxidative DNA modification estimated by 8-oxo-7,8-dihydro-2'-deoxyguanosine excretion.

BACKGROUND: Reactive oxygen species from, e.g. tobacco smoke are suggested to be involved in carcinogenesis by oxidative modification of DNA. The urinary excretion rate of the oxidized nucleoside 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) has been validated as a biomarker of the rate of oxidative DNA modification with mechanistic relation to carcinogenesis. In cross-sectional studies, the urinary excretion rate of 8-oxodG has been shown to be elevated in smokers compared with non-smokers. PURPOSE: In this randomised, controlled smoking cessation study, we investigated whether cigarette smoking per se causes oxidative DNA modification. METHODS: Of the 182 healthy smokers included, 100 were randomized to quit smoking after baseline samples had been taken, and 82 were randomized to continue usual smoking. Before the start of the study and after 4 weeks, the subjects collected 24-h urine samples that were analysed for 8-oxodG content by high-pressure liquid chromatography with electrochemical detection. The subjects randomized to smoking cessation were followed up after 26 weeks. RESULTS: Four weeks of smoking cessation resulted in a 21% decrease in 8-oxodG excretion rate (from mean +/- SD, 30.5 +/- 13.9 to 24.1 +/- 10.5 nmol/24 h, P < 0.001) in 58 quitters included in per-protocol data analysis. Sixty-five continued smokers included in per-protocol analysis showed a 9% decrease in 8-oxodG excretion rate (from 31.6 +/- 13.2 to 28.7 +/- 12.6 nmol/24 h, P = 0.026). After 4 weeks, the 8-oxodG excretion rate was 16% (95% confidence interval 4 to 28%) higher in the continued smokers than in the quitters (P = 0.0085, ANCOVA), demonstrating the effect of smoking per se. A 23% (P < 0.005) decrease in 8-oxodG excretion rate was sustained for 26 weeks in 27 quitters who completed the study. CONCLUSION: Smoking cessation significantly reduces the urinary excretion rate of 8-oxodG, giving direct and controlled evidence that cigarette smoking causes an increased rate of oxidative DNA modification. This could represent a mechanism by which tobacco smoke is carcinogenic.