Possible carcinogenic effect of 6-mercaptopurine on bone marrow stem cells: relation to thiopurine metabolism

A Case Report of Follicular Lymphoma in a Crohn's Disease Patient Treated With Azathioprine

Inflammatory bowel disease (IBD) is an autoimmune disorder marked by chronic inflammation affecting the intestines. Crohn's disease (CD) and ulcerative colitis (UC) fall under the IBD umbrella, necessitating diverse treatments, including steroids, immunomodulators like 6-mercaptopurine (6-MP) and azathioprine (AZA), and biological agents. The prolonged use of immunomodulators, such as AZA, is associated with an elevated risk of developing lymphomas. This case report centers on a 77-year-old gentleman regularly monitored by Gastroenterology, undergoing long-term AZA therapy for CD management. He presented with palate swelling and acute-on-chronic back pain, diagnosed with follicular lymphoma in the palate with metastasis. Palliative radiotherapy was administered for the paraspinal lesion, and the patient is currently stable. In conclusion, this case underscores the importance of recognizing the heightened risk of neoplasms, especially lymphomas, in patients undergoing prolonged immunomodulator therapy. It emphasizes the need for a vigilant and comprehensive approach to patient care, transcending conventional paradigms.

Association Between Genetically Predicted Expression of TPMT and Azathioprine Adverse Events

Polymorphisms thiopurine-S-methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15) can increase the risk of azathioprine myelotoxicity, but little is known about other genetic factors that increase risk for azathioprine-associated side effects. PrediXcan is a gene-based association method that estimates the expression of individuals' genes and examines their correlation to specified phenotypes. As proof of concept for using PrediXcan as a tool to define the association between genetic factors and azathioprine side effects, we aimed to determine whether the genetically predicted expression of TPMT or NUDT15 was associated with leukopenia or other known side effects. In a retrospective cohort of 1364 new users of azathioprine with EHR-reported White race, we used PrediXcan to impute expression in liver tissue, tested its association with pre-specified phecodes representing known side effects (e.g., skin cancer), and completed chart review to confirm cases. Among confirmed cases, patients in the lowest tertile (i.e., lowest predicted) of TPMT expression had significantly higher odds of developing leukopenia (OR=3.30, 95%CI: 1.07-10.20, p=0.04) versus those in the highest tertile; no other side effects were significant. The results suggest that this methodology could be deployed on a larger scale to uncover associations between genetic factors and drug side effects for more personalized care.

Pharmacogenomics in Children

Historically genetics has not been considered when prescribing drugs for children. However, it is clear that genetics are not only an important determinant of disease in children but also of drug response for many important drugs that are core agents used in the therapy of common problems in children. Advances in therapy and in the ethical construct of children's research have made pharmacogenomic assessment for children much easier to pursue. It is likely that pharmacogenomics will become part of the therapeutic decision-making process for children, notably in areas such as childhood cancer where weighing benefits and risks of therapy is crucial.

NUDT15 variants confer high incidence of second malignancies in children with acute lymphoblastic leukemia

NUDT15 variants may confer a risk of second cancers after treatment with 6-MP in patients with ALL.

The effect of genetic variation on second malignant neoplasms (SMNs) remains unclear. First, we identified the pathogenic germline variants in cancer-predisposing genes among 15 children with SMNs after childhood leukemia/lymphoma using whole-exome sequencing. Because the prevalence was low, we focused on the association between SMNs and NUDT15 in primary acute lymphoblastic leukemia (ALL) cases. NUDT15 is one of the 6-mercaptopurine (6-MP) metabolic genes, and its variants are common in East Asian individuals. The prevalence of NUDT15 hypomorphic variants was higher in patients with SMNs (n = 14; 42.9%) than in the general population in the gnomAD database (19.7%; P = .042). In the validation study with a cohort of 438 unselected patients with ALL, the cumulative incidence of SMNs was significantly higher among those with (3.0%; 95% confidence interval [CI], 0.6% to 9.4%) than among those without NUDT15 variants (0.3%; 95% CI, 0.0% to 1.5%; P = .045). The 6-MP dose administered to patients with ALL with a NUDT15 variant was higher than that given to those without SMNs (P = .045). The 6-MP–related mutational signature was observed in SMN specimens after 6-MP exposure. In cells exposed to 6-MP, a higher level of 6-MP induced DNA damage in NUDT15-knockdown induced pluripotent stem cells. Our study indicates that NUDT15 variants may confer a risk of SMNs after treatment with 6-MP in patients with ALL.

Risk of malignancies in patients with inflammatory bowel disease who used thiopurines as compared with other indications: a territory-wide study

AIMS

Thiopurines are believed to increase cancer risks, but data from Asian patients are sparse. We determined the risks of malignancies in thiopurine users with inflammatory bowel disease (IBD) or other indications from Hong Kong.

METHODS

All patients who had received thiopurines between 2005 and 2009 in Hong Kong were identified from local electronic healthcare database. Patients were followed from the start date of thiopurines until death or end of study in 2017. We excluded patients with baseline malignancy. Standardized incidence ratios (SIR) and the corresponding 95% confidence intervals (CI) of all malignancies were computed against matched local general population from the cancer registry. Patients in the same diagnosis category but not exposed to thiopurines were included as controls.

RESULTS

There were 7452 thiopurines users (median age 47.0 years), including 595 IBD patients, with a median follow-up of 11.2 years. Of them, 684 (9.2%) developed malignancies with an overall SIR of 2.30 (95% CI 2.13-2.48). The SIR in IBD patients who used thiopurines was 2.37 (95% CI 1.71-3.18) as compared with non-users (SIR 1.35, 95% CI 1.05-1.72). Highest risk of malignancies was observed in post-transplant patients (SIR 3.83, 95% CI 3.34-4.35), and lower risks were seen in patients with rheumatological diseases (SIR 1.46, 95% CI 1.02-2.02).

CONCLUSION

IBD patients in Hong Kong who used thiopurines had 2.37-fold increase in risk of malignancies than the general population, which was higher than non-users and different from thiopurine users for other indications.

Precision medicine for rheumatologists: lessons from the pharmacogenomics of azathioprine

Precision medicine aims to personalize treatment for both effectiveness and safety. As a critical component of this emerging initiative, pharmacogenomics seeks to guide drug treatment based on genetics. In this review article, we give an overview of pharmacogenomics in the setting of an immunosuppressant frequently prescribed by rheumatologists, azathioprine. Azathioprine has a narrow therapeutic index and a high risk of adverse events. By applying candidate gene analysis and unbiased approaches, researchers have identified multiple variants associated with an increased risk for adverse events associated with azathioprine, particularly bone marrow suppression. Variants in two genes, TPMT and NUDT15, are widely recognized, leading drug regulatory agencies and professional organizations to adopt recommendations for testing before initiation of azathioprine therapy. As more gene-drug interactions are discovered, our field will continue to face the challenge of balancing benefits and costs associated with genetic testing. However, novel approaches in genomics and the integration of clinical and genetic factors into risk scores offer unprecedented opportunities for the application of pharmacogenomics in routine practice. Key Points • Pharmacogenomics can help us understand how individuals' genetics may impact their response to medications. • Azathioprine is a success story for the clinical implementation of pharmacogenomics, particularly the effects of TPMT and NUDT15 variants on myelosuppression. • As our knowledge advances, testing and dosing recommendations will continue to evolve, with our field striving to balance costs and benefits to patients. • As we aim toward the goals of precision medicine, future research may integrate increasingly individualized traits-including clinical and genetic characteristics-to predict the safety and efficacy of particular medications for individual patients.

Drug-Related Carcinogenesis: Risk Factors and Approaches for Its Prevention

The review summarizes the data on the role of metabolic and repair systems in the mechanisms of therapy-related carcinogenesis and the effect of their polymorphism on the cancer development risk. The carcinogenic activity of different types of drugs, from the anticancer agents to analgesics, antipyretics, immunomodulators, hormones, natural remedies, and non-cancer drugs, is described. Possible approaches for the prevention of drug-related cancer induction at the initiation and promotion stages are discussed.

Children with low-risk acute lymphoblastic leukemia are at highest risk of second cancers

BACKGROUND

The improved survival rates for childhood acute lymphoblastic leukemia (ALL) may be jeopardized by the development of a second cancer, which has been associated with thiopurine therapy.

PROCEDURE

We retrospectively analyzed three sequential Nordic Society of Paediatric Haematology and Oncology's protocols characterized by increasing intensity of thiopurine-based maintenance therapy. We explored the risk of second cancer in relation to protocols, risk group, thiopurine methyltransferase (TPMT) activity, ALL high hyperdiploidy (HeH), and t(12;21)[ETV6/RUNX1].

RESULTS

After median 9.5 years (interquartile range, 5.4-15.3 yrs) of follow-up, 40 of 3,591 patients had developed a second cancer, of whom 38 had non-high-risk B-cell precursor ALL. Patients with standard-risk ALL, who received the longest maintenance therapy, had the highest adjusted hazard of second cancer (hazard ratio [HR], intermediate vs. standard risk: 0.16, 95% CI: 0.06-0.43, P < 0.001; HR, high vs. standard risk: 0.09, 95% CI: 0.02-0.49, P = 0.006); no significant effects of protocol, age, or white blood cell count at diagnosis, ALL HeH, or t(12;21)[ETV6/RUNX1] were observed. A subset analysis on the patients with standard-risk ALL did not show an increased hazard of second cancer from either HeH or t(12;21) (adjusted HR 2.02, 95% CI: 0.69-5.96, P = 0.20). The effect of low TPMT low activity was explored in patients reaching maintenance therapy in clinical remission (n = 3,368); no association with second cancer was observed (adjusted HR 1.43, 95% CI: 0.54-3.76, P = 0.47).

CONCLUSIONS

The rate of second cancer was generally highest in patients with low-risk ALL, but we could not identify a subset at higher risk than others.

Blastic transformation of juvenile myelomonocytic leukemia caused by the copy number gain of oncogenic KRAS

Previous studies have reported several cases of juvenile myelomonocytic leukemia (JMML) developing blastic transformation during an indolent clinical course, but the underlying mechanism of transformation is still not well understood. In this report, we describe a case of JMML with blastic transformation possibly caused by additional copy number gains of the KRAS mutant allele. We have discovered that the copy number gain of the mutant allele is an additional possible cause of blastic transformation in JMML.

Thiopurine S-methyltransferase polymorphisms in acute lymphoblastic leukemia, inflammatory bowel disease and autoimmune disorders: influence on treatment response

The thiopurine S-methyltransferase (TPMT) gene encodes for the TPMT enzyme that plays a crucial role in the metabolism of thiopurine drugs. Genetic polymorphisms in this gene can affect the activity of the TPMT enzyme and have been correlated with variability in response to treatment with thiopurines. Advances in the pharmacogenetics of TPMT allowed the development of dosing recommendations and treatment strategies to optimize and individualize prescribing thiopurine in an attempt to enhance treatment efficacy while minimizing toxicity. The influence of genetic polymorphisms in the TPMT gene on clinical outcome has been well-documented and replicated in many studies. In this review, we provide an overview of the evolution, results, conclusions and recommendations of selected studies that investigated the influence of TPMT pharmacogenetics on thiopurine treatment in acute lymphoblastic leukemia, inflammatory bowel disease and autoimmune disorders. We focus mainly on prospective studies that explored the impact of individualized TPMT-based dosing of thiopurines on clinical response. Together, these studies demonstrate the importance of preemptive TPMT genetic screening and subsequent dose adjustment in mitigating the toxicity associated with thiopurine treatment while maintaining treatment efficacy and favorable long-term outcomes. In addition, we briefly address the cost-effectiveness of this pharmacogenetics approach and its impact on clinical practice as well as the importance of recent breakthrough advances in sequencing and genotyping techniques in refining the TPMT genetic screening process.

Hepatotoxicity During Maintenance Therapy and Prognosis in Children With Acute Lymphoblastic Leukemia

Hepatotoxicity is a known toxicity to treatment of childhood acute lymphoblastic leukemia. Hepatotoxicity occurs during maintenance therapy and is caused by metabolites of 6-Mercaptopurine (6 MP) and Methotrexate (MTX). Our objective was to investigate the association between alanine aminotransferases (ALAT) levels and relapse rate. We included 385 patients enrolled in the NOPHO ALL-92 protocol. Data on ALAT levels, 6 MP and MTX doses, cytotoxic MTX/6 MP metabolites, and thiopurine methyltransferase (TPMT) activity were prospectively registered. In total, 91% of the patients had a mean ALAT (mALAT) level above upper normal limit (40 IU/L) and ALAT levels were positively correlated to 6 MP doses (rs=0.31; P<0.001). In total, 47 patients suffered a relapse, no difference in mALAT levels were found in these compared with nonrelapse patients (median, 107 vs. 98 IU/L; P=0.39). mALAT levels in patients classified as TPMT high activity (TPMT) were higher than in TPMT low-activity patients (median, 103 vs. 82 IU/L; P=0.03). In a Cox regression model risk of relapse was not associated with ALAT levels (P=0.56). ALAT levels increased 2.7%/month during the last year of maintenance therapy (P<0.001). In conclusion, elevated ALAT levels are associated with TPMT and may indicate treatment adherence in these patients. If liver function is normal, elevated ALAT levels should not indicate treatment adaptation.

Thiopurine Metabolism in the Era of Combotherapy

6-thioguanine nucleotides levels are associated with clinical remission in patients with inflammatory bowel disease (IBD) on thiopurine monotherapy. Recently, few studies investigated the interaction between thiopurine metabolism and anti-tumor necrosis factor therapy among patients with IBD on combotherapy. Two studies demonstrated that infliximab therapy increases 6-thioguanine nucleotides level, while such effect could not be observed with adalimumab. Three studies showed that a Delta mean corpuscular volume >7 and high 6-thioguanine nucleotides levels are associated with favorable outcomes, i.e., greater mucosal healing rates, and have a positive impact on the pharmacokinetics of infliximab. These results suggest a synergistic effect between thiopurine metabolism and anti-tumor necrosis factor therapy, especially with infliximab. We propose here some algorithms for clinical practice integrating thiopurine metabolism in patients with IBD on combotherapy. Further randomized controlled trials are needed to further investigate the relationships between thiopurine metabolism and anti-tumor necrosis factor therapy and to establish the clinical utility of measuring thiopurines' metabolites in these patients in clinical practice. Whether measuring thiopurine metabolism can be used to guide decision-making in patients with IBD on combotherapy when considering drug de-escalation or discontinuation will require further investigation.

Risk of myeloid neoplasms after solid organ transplantation

Solid organ transplant recipients have elevated cancer risks, owing in part to pharmacologic immunosuppression. However, little is known about risks for hematologic malignancies of myeloid origin. We linked the US Scientific Registry of Transplant Recipients with 15 population-based cancer registries to ascertain cancer occurrence among 207 859 solid organ transplants (1987-2009). Solid organ transplant recipients had a significantly elevated risk for myeloid neoplasms, with standardized incidence ratios (SIRs) of 4.6 (95% confidence interval 3.8-5.6; N=101) for myelodysplastic syndromes (MDS), 2.7 (2.2-3.2; N=125) for acute myeloid leukemia (AML), 2.3 (1.6-3.2; N=36) for chronic myeloid leukemia and 7.2 (5.4-9.3; N=57) for polycythemia vera. SIRs were highest among younger individuals and varied by time since transplantation and organ type (Poisson regression P<0.05 for all comparisons). Azathioprine for initial maintenance immunosuppression increased risk for MDS (P=0.0002) and AML (2-5 years after transplantation, P=0.0163). Overall survival following AML/MDS among transplant recipients was inferior to that of similar patients reported to US cancer registries (log-rank P<0.0001). Our novel finding of increased risks for specific myeloid neoplasms after solid organ transplantation supports a role for immune dysfunction in myeloid neoplasm etiology. The increased risks and inferior survival should heighten clinician awareness of myeloid neoplasms during follow-up of transplant recipients.

Mercaptopurine/Methotrexate maintenance therapy of childhood acute lymphoblastic leukemia: clinical facts and fiction

The antileukemic mechanisms of 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy are poorly understood, but the benefits of several years of myelosuppressive maintenance therapy for acute lymphoblastic leukemia are well proven. Currently, there is no international consensus on drug dosing. Because of significant interindividual and intraindividual variations in drug disposition and pharmacodynamics, vigorous dose adjustments are needed to obtain a target degree of myelosuppression. As the normal white blood cell counts vary by patients' ages and ethnicity, and also within age groups, identical white blood cell levels for 2 patients may not reflect the same treatment intensity. Measurements of intracellular levels of cytotoxic metabolites of 6MP and MTX can identify nonadherent patients, but therapeutic target levels remains to be established. A rise in serum aminotransferase levels during maintenance therapy is common and often related to high levels of methylated 6MP metabolites. However, except for episodes of hypoglycemia, serious liver dysfunction is rare, the risk of permanent liver damage is low, and aminotransferase levels usually normalize within a few weeks after discontinuation of therapy. 6MP and MTX dose increments should lead to either leukopenia or a rise in aminotransferases, and if neither is experienced, poor treatment adherence should be considered. The many genetic polymorphisms that determine 6MP and MTX disposition, efficacy, and toxicity have precluded implementation of pharmacogenomics into treatment, the sole exception being dramatic 6MP dose reductions in patients who are homozygous deficient for thiopurine methyltransferase, the enzyme that methylates 6MP and several of its metabolites. In conclusion, maintenance therapy is as important as the more intensive and toxic earlier treatment phases, and often more challenging. Ongoing research address the applicability of drug metabolite measurements for dose adjustments, extensive host genome profiling to understand diversity in treatment efficacy and toxicity, and alternative thiopurine dosing regimens to improve therapy for the individual patient.

Pharmacogenetically based dosing of thiopurines in childhood acute lymphoblastic leukemia: influence on cure rates and risk of second cancer

BACKGROUND

Previous studies have indicated that patients with thiopurine methyltransferase (TPMT) low activity (TPMT(LA)) have reduced risk of relapse but increased risk of second malignant neoplasm (SMN) compared to patients with TPMT wild-type (TPMT(WT)) when treated with 6 MP maintenance therapy starting doses of 75 mg/m(2)/day. To reduce SMN risk, 6MP starting doses were reduced to 50 mg/m(2)/day for patients with TPMT heterozygosity in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL2000 protocol.

PROCEDURE

We explored the pattern of SMN and relapse in the NOPHO ALL2000 protocol (n = 674) and NOPHO ALL92 protocol (n = 601) in relation to TPMT pheno- and/or genotype.

RESULTS

The overall risk of any event did not differ significantly between the two protocols. However, in event pattern analyses considering only the patients with TPMT(LA) who experienced relapse or SMN, the risk of SMN versus leukemia relapse was significantly lower in the ALL2000 cohort for patients with a 6MP starting dose <75 mg/m(2)/day when compared to the patients in ALL92 (relapse (n = 11) and SMN (n = 0) in ALL2000 versus relapse (n = 5) and SMN (n = 4) in ALL92, P = 0.03). Furthermore, the 8-year cumulative incidence of relapse for patients with TPMT(LA) was significantly higher in the ALL2000 compared to the ALL92 cohort (19.7% (11.6-33.3%) vs. 6.7% (2.9-15.5%), P = 0.03).

CONCLUSION

This study indicates that reducing 6MP starting dose for patients with TPMT(LA) may reduce SMN risk but lead to a relapse risk similar to that of patients with TPMT(WT).

Pharmacogenomics and adverse drug reactions in children

Adverse drug reactions are a common and important complication of drug therapy in children. Over the past decade it has become increasingly apparent that genetically controlled variations in drug disposition and response are important determinants of adverse events for many important adverse events associated with drug therapy in children. While this research has been difficult to conduct over the past decade technical and ethical evolution has greatly facilitated the ability of investigators to conduct pharmacogenomic studies in children. Some of this research has already resulted in changes in public policy and clinical practice, for example in the case of codeine use by mothers and children. It is likely that the use of pharmacogenomics to enhance drug safety will first be realized among selected groups of children with high rates of drug use such as children with cancer, but it also likely that this research will be extended to other groups of children who have high rates of drug utilization and as well as providing insights into the mechanisms and pathophysiology of adverse drug reactions in children.

Lymphohematopoietic cancers induced by chemicals and other agents and their implications for risk evaluation: An overview

Lymphohematopoietic neoplasia are one of the most common types of cancer induced by therapeutic and environmental agents. Of the more than 100 human carcinogens identified by the International Agency for Research on Cancer, approximately 25% induce leukemias or lymphomas. The objective of this review is to provide an introduction into the origins and mechanisms underlying lymphohematopoietic cancers induced by xenobiotics in humans with an emphasis on acute myeloid leukemia, and discuss the implications of this information for risk assessment. Among the agents causing lymphohematopoietic cancers, a number of patterns were observed. Most physical and chemical leukemia-inducing agents such as the therapeutic alkylating agents, topoisomerase II inhibitors, and ionizing radiation induce mainly acute myeloid leukemia through DNA-damaging mechanisms that result in either gene or chromosomal mutations. In contrast, biological agents and a few immunosuppressive chemicals induce primarily lymphoid neoplasms through mechanisms that involve alterations in immune response. Among the environmental agents examined, benzene was clearly associated with acute myeloid leukemia in humans, with increasing but still limited evidence for an association with lymphoid neoplasms. Ethylene oxide and 1,3-butadiene were linked primarily to lymphoid cancers. Although the association between formaldehyde and leukemia remains controversial, several recent evaluations have indicated a potential link between formaldehyde and acute myeloid leukemia. The four environmental agents examined in detail were all genotoxic, inducing gene mutations, chromosomal alterations, and/or micronuclei in vivo. Although it is clear that rapid progress has been made in recent years in our understanding of leukemogenesis, many questions remain for future research regarding chemically induced leukemias and lymphomas, including the mechanisms by which the environmental agents reviewed here induce these diseases and the risks associated with exposures to such agents.

Pharmacogenomics in children

Historically genetics has not been considered when prescribing drugs for children. However, it is clear that genetics are not only an important determinant of disease in children but also of drug response for many important drugs that are core agents used in the therapy of common problems in children. Advances in therapy and in the ethical construct of children's research have made pharmacogenomic assessment for children much easier to pursue. It is likely that pharmacogenomics will become part of the therapeutic decision making process for children, notably in areas such as childhood cancer where the benefits and risks of therapy are considerable.

Thiopurines related malignancies in inflammatory bowel disease: Local experience in Granada, Spain

AIM: To investigate the incidence of neoplasms in inflammatory bowel disease (IBD) patients and the potential causative role of thiopurines.

METHODS: We performed an observational descriptive study comparing the incidence of malignancies in IBD patients treated with thiopurines and patients not treated with these drugs. We included 812 patients which were divided in two groups depending on whether they have received thiopurines or not. We have studied basal characteristics of both groups (age when the disease was diagnosed, sex, type of IBD, etc.) and treatments received (Azathioprine, mercaptopurine, infliximab, adalimumab or other immunomodulators), as well as neoplasms incidence. Univariate analysis was performed with the student t test, χ² test or Wilcoxon exact test as appropriate. A logistic regression analysis was performed as multivariate analysis. Statistical significance was establish at P values of less than 0.05, and 95%CI were used for the odds ratios.

RESULTS: Among 812 patients included, 429 (52.83%) have received thiopurines: 79.5% azathioprine, 14% mercaptopurine and 6.5% both drugs. 44.76% of patients treated with thiopurines and 46, 48% of patients who did not receive this treatment were women (P > 0.05). The proportion of ulcerative colitis patients treated with thiopurines was 30.3% compare to 66. 67% of patients not treated (P < 0.001). Mean azathioprine dose was 123.79 ± 36.5 mg/d (range: 50-250 mg/d), mean usage time was 72.16 ± 55.7 mo (range: 1-300 mo) and the accumulated dose along this time was 274.32 ± 233.5 g (1.5-1350 g). With respect to mercaptopurine, mean dose was 74.7 ± 23.9 mg/d (range: 25-150 mg/d), mean usage time of 23.37 ± 27.6 mo (range: 1-118 mo), and the accumulated dose along this time was 52.2 ± 63.5 g (range: 1.5-243 g). Thiopurine S-methyltransferase activity was tested in 66% of patients treated with thiopurines, among which 98.2% had an intermediate or high activity. Among the patients treated with thiopurines, 27.27% (112 patients) and 11.66% (50 patients) received treatment with Infliximab and Adalimumab respectively, but only 1.83% (7 patients) and 0.78% (3 patients) received these drugs in the group of patients who did not received thiopurines (P < 0.001 and P < 0.001 respectively). Finally, 6.8% (29 patients) among those treated with thiopurines have received other immunesupresants (Methotrexate, Tacrolimus, Cyclosporin), compare to 1% (4 patients) of patients not treated with thiopurines (P < 0.001). Among patients treated with thiopurines, 3.97% developed a malignancy, and among those not treated neoplasms presented in 8.1% (P = 0.013). The most frequent neoplasms were colorectal ones (12 cases in patients not treated with thiopurines but none in treated, P < 0.001) followed by non-melanoma skin cancer (8 patients in treated with thiopurines and 6 in not treated, P > 0.05).

CONCLUSION: In our experience, thiopurine therapy did not increase malignancies development in IBD patients, and was an efective and safe treatment for these diseases.

Azathioprine-associated myelodysplastic syndrome in two patients with ulcerative colitis

Azathioprine is a commonly used immunosuppressive agent in post-transplantation regimens and autoimmune diseases. An increased risk of lymphoma with thiopurine therapy in patients with inflammatory bowel disease has been described previously; however, there are few reported cases of azathioprine therapy-related myelodysplastic syndrome and acute myeloid leukaemia. We report two patients with ulcerative colitis who subsequently developed azathioprine-related myelodysplastic syndrome. It is imperative that gastroenterologists remain vigilant for this rare complication as this subset of patients has a particularly poor prognosis. These cases are also important in considering the risk of open-ended thiopurine therapy.

Cancer pharmacogenomics in children: research initiatives and progress to date

Over the last few decades, cure rates for pediatric cancer have increased dramatically, and now over 80 % of children with cancer are cured of their disease. This improvement in cure has come with a significant cost, with many children suffering irreversible, life-threatening, or long-lasting toxicities due to the medications required during their treatment. In the last 2 decades, major technological advances in genomics and the mapping of the human genome have made it possible to identify genetic differences between children in order to investigate differing responses to cancer therapy and to help explain why children treated with the same medications can have different outcomes. The emerging field of pharmacogenomics has had many important findings in pediatric cancer. The focus of this review is drug toxicity in pediatric cancer and the use of pharmacogenomics to reduce these adverse drug reactions, with a specific focus on thiopurines, methotrexate, cisplatin, vincristine and anthracyclines. Future areas of research and the need for international collaboration are discussed.

Immunosuppression in inflammatory bowel disease: how much is too much?

PURPOSE OF REVIEW

Current treatment approaches favor the early introduction of immunomodulators and/or antitumor necrosis factor (TNF) agents. There is now strong evidence showing that combination therapy appears to be more effective than monotherapy in both ulcerative colitis and Crohn's disease. However, there are concerns associated with this strategy, and eventually the following questions will emerge when discussing therapeutic options with our patients: is it safe to maintain these therapies for the long-term?; how long should we maintain therapy?; and if we decide to stop or de-escalate therapy, what strategy should we use?

RECENT FINDINGS

During the past year new evidence regarding safety of long-term therapy with anti-TNF and immunomodulators, and predictors of relapse following therapy discontinuation have become available.

SUMMARY

In this review we aim to discuss some of the safety concerns related to the use of immunosuppressive drugs used in inflammatory bowel disease, as well as the possible strategy for de-escalation or discontinuation therapy. Eventually, choosing to stop either the anti-TNF or the immunomodulator is a case-by-case decision based on the estimated risk-benefit ratio. In addition to the identified predictors of relapse after therapy discontinuation, other considerations such as long-term safety, cost, and natural history of the disease must be brought into this discussion.

Thiopurine methyltransferase predicts the extent of cytotoxicty and DNA damage in astroglial cells after thioguanine exposure

Thiopurine methyltransferase (Tpmt) is the primary enzyme responsible for deactivating thiopurine drugs. Thiopurine drugs (i.e., thioguanine [TG], mercaptopurine, azathioprine) are commonly used for the treatment of cancer, organ transplant, and autoimmune disorders. Chronic thiopurine therapy has been linked to the development of brain cancer (most commonly astrocytomas), and Tpmt status has been associated with this risk. Therefore, we investigated whether the level of Tpmt protein activity could predict TG-associated cytotoxicity and DNA damage in astrocytic cells. We found that TG induced cytotoxicity in a dose-dependent manner in Tpmt^+/+, Tpmt^+/− and Tpmt^−/− primary mouse astrocytes and that a low Tpmt phenotype predicted significantly higher sensitivity to TG than did a high Tpmt phenotype. We also found that TG exposure induced significantly more DNA damage in the form of single strand breaks (SSBs) and double strand breaks (DSBs) in primary astrocytes with low Tpmt versus high Tpmt. More interestingly, we found that Tpmt^+/− astrocytes had the highest degree of cytotoxicity and genotoxicity (i.e., IC₅₀, SSBs and DSBs) after TG exposure. We then used human glioma cell lines as model astroglial cells to represent high (T98) and low (A172) Tpmt expressers and found that A172 had the highest degree of cytoxicity and SSBs after TG exposure. When we over-expressed Tpmt in the A172 cell line, we found that TG IC₅₀ was significantly higher and SSB's were significantly lower as compared to mock transfected cells. This study shows that low Tpmt can lead to greater sensitivity to thiopurine therapy in astroglial cells. When Tpmt deactivation at the germ-line is considered, this study also suggests that heterozygosity may be subject to the greatest genotoxic effects of thiopurine therapy.

Optimizing 6-mercaptopurine and azathioprine therapy in the management of inflammatory bowel disease

The thiopurine drugs, 6-mercaptopurine (6-MP) and azathioprine, are efficacious in the arsenal of inflammatory bowel disease (IBD) therapy. Previous reports indicate that 6-thioguanine nucleotide (6-TGN) levels correlate with therapeutic efficacy, whereas high 6-methylmercaptopurine (6-MMP) levels are associated with hepatotoxicity and myelotoxicity. Due to their complex metabolism, there is wide individual variation in patient response therein, both in achieving therapeutic drug levels as well as in developing adverse reactions. Several strategies to optimize 6-TGN while minimizing 6-MMP levels have been adopted to administer the thiopurine class of drugs to patients who otherwise would not tolerate these drugs due to side-effects. In this report, we will review different approaches to administer the thiopurine medications, including the administration of 6-mercaptopurine in those unsuccessfully treated with azathioprine; co-administration of thiopurine with allopurinol; co-administration of thiopurine with anti-tumor necrosis factor α; 6-TGN administration; desensitization trials; and split dosing of 6-MP.

Second neoplasm in children treated in EORTC 58881 trial for acute lymphoblastic malignancies: low incidence of CNS tumours

BACKGROUND

Intensive chemotherapy has markedly improved the survival of children with acute lymphoblastic leukaemia (ALL) or lymphoblastic lymphoma (LL). Evaluation of late effects and analysis of factors contributing to their occurrence has become of major importance. Second neoplasm (SN) belongs to the most severe late events.

PROCEDURE

We report the incidence of SN which occurred in patients recruited in EORTC trial 58881 for children with ALL or LL. The front-line treatment regimen was adapted from the BFM protocol, but did not include cranial radiotherapy, even in patients with initial involvement of the central nervous system. A total of 2,216 patients were recruited, of whom 2,136 achieved complete remission (CR).

RESULTS

At a median follow-up of 7.5 years, 22 (1%) patients developed a SN: 20 during or after completion of front-line therapy and 2 in second CR, after relapse treatment including haematopoietic stem cell transplantation (HSCT). Ten patients developed acute myeloblastic leukaemia. Only one SN, a glioblastoma, was a brain tumour. Other SN were: two Hodgkin lymphomas, one non-Hodgkin lymphoma, two thyroid cancers, one osteosarcoma, two soft tissue sarcomas, one Ewing sarcoma, one cutaneous histiocytosis and one peritoneal carcinomatosis. The cumulative incidences of SN at 5, 8 and 13 years after registration were 0.8% (SE 0.2%), 1.0% (SE 0.2%) and 3.0% (SE 1.9%), respectively.

CONCLUSION

The overall incidence rate of SN is comparable to that reported previously. In spite of short follow-up time, the low incidence of brain tumours might be related to the omission of cranial radiotherapy.

New Nanomedicine Approaches Using Gold-thioguanine Nanoconjugates as Metallo-ligands

Gold-thioguanine nanoconjugates (AuNP-TG) of size 3-4 nm were synthesized and the ratio between gold and 6-Thioguanine (TG) was estimated as ~1:1.5 using a cyanide digestion method and confirmed by flame atomic absorption spectroscopic analysis. AuNP-TG constructs showed high in vitro stability under different pH conditions and biologically relevant solutions for a period of 24 hours. Reaction of AuNP-TG with europium or platinum salts resulted in the formation of organized self-assembled metallo-networks.

Epidemiology of therapy-related myeloid neoplasms after treatment for pediatric acute lymphoblastic leukemia in the nordic countries

Of 1614 Nordic children with ALL that were treated according to the NOPHO ALL92 protocol, 20 developed an SMN (cumulative risk at 12 years: 1.6%). Sixteen of the twenty SMNs were acute myeloid leukemias or myelodysplasias, and 9 of these had either monosomy 7 (n=7) or 7q deletions (n=2). In Cox multivariate analysis longer duration of oral MTX/6MP maintenance therapy (p=0.02; being longest for standard risk patients) and presence of high-hyperdiploidy (p=0.07) were related to an increased risk of SMN. In 524 patients we determined the erythrocyte activity of thiopurine methyltransferase (TPMT), which methylates 6MP and its metabolites, and thus reduces cellular levels of cytotoxic 6-thioguanine nucleotides. The TPMT activity was significantly lower in those that did compared to those that did not develop an SMN (Median: 12.1 vs 18.1 IU/ml; p=0.02). Among 427 TPMT wild type patients, those who developed SMN received higher 6MP doses than the remaining (69.7 vs 60.4 mg/m², p=0.03), which may reflect increased levels of methylated metabolites that inhibit purine de novo synthesis and thus enhance incorporation of 6-thioguanine nucleotides into DNA. In conclusion, the duration and intensity of 6MP/MTX maintenance therapy of childhood ALL may influence the risk of SMN.

The genetics of inflammatory bowel disease: diagnostic and therapeutic implications

BACKGROUND

The genetics of inflammatory bowel diseases (IBD) has brought new insight into the spectrum of disease phenotypes that are collectively labeled as either Crohn's disease or ulcerative colitis. In concert with the pharmacogenomics of drug therapy, it has led clinicians to develop the notion of a more tailored approach to therapy.

DATA SOURCES

Articles were searched from PubMed (1995-2010) with key words "inflammatory bowel diseases", "Genetics", "pharmacogenomics".

RESULTS

Among all the putative susceptibility loci, the NOD2 gene has been the most studied and linked to an aggressive form of stricturing and perforating disease of the ileum. Other potential gene polymorphisms, including those encoding for the interleukin-23 receptor, have lent themselves to the recent development of potential novel immunosuppressive therapies. While the linkage of a number of autophagy genes with either Crohn's disease or ulcerative colitis has provided insight into the innate adaptive immune pathway's response to commensual intestinal bacteria. Pharmacogenetic polymorphisms of azathioprine metabolism have been shown to predict toxicity to anti-metabolite therapy. Patients with absent thiopurine methyl transferase enzyme activity are at risk for irreversible bone marrow suppression, and are not considered good candidates for either 6-mercaptopurine (6-MP) or azathioprine therapy.

CONCLUSIONS

Ultimately, the correlation between these genotypes and clinical phenotype of disease will inevitably lead to an improved understanding of disease natural history and a more tailored approach to therapy. Although there is ongoing debate as to whether these inherent differences in enzyme activity can predict responsiveness to anti-metabolite therapy, some gastroenterologists do find value in 6-MP metabolite testing as a means of monitoring patient compliance and tailoring the dose of anti-metabolite therapy based on a perceived therapeutic window. In the future, patients with IBD will ultimately be categorized based on their genomic imprint to allow for a better delineation of disease phenotype. Furthermore, the application pharmacogenomics of drug therapy into clinical practice will be pivotal in maximizing treatment response while avoiding untoward side-effects.

Review article: malignancy on thiopurine treatment with special reference to inflammatory bowel disease

BACKGROUND

Immunosuppression is a risk factor for carcinogenesis. Thiopurines specifically contribute to this. As thiopurines are used more aggressively in the treatment of IBD, it is likely that we will see more thiopurine-related malignancy.

AIM

To review the literature, exploring how immunosuppression, thiopurines specifically, might cause cancer and which malignancies occur in practice, placing specific emphasis on IBD cohorts.

METHODS

Search terms included 'malignancy' 'cancer' 'azathioprine' 'mercaptopurine' 'tioguanine (thioguanine)' 'thiopurine' and 'inflammatory bowel disease' 'Crohn's disease' 'ulcerative colitis'. We also searched for specific cancers (lymphoma, colorectal cancer, skin cancer, cervical cancer) and reviewed the reference lists of the articles detected.

RESULTS

Immunosuppression is associated with an increased risk of cancer. Thiopurines are associated with specific additional risks. In IBD cohorts, very few thiopurine-related malignancies have been reported. However, studies suggest a relative risk of 4-5 for lymphoma. This still translates into a low actual risk, (one extra lymphoma in every 300-1400 years of thiopurine treatment).

CONCLUSIONS

Whilst we must be aware of this risk and counsel our patients appropriately, thiopurines remain a mainstay of IBD therapy. We present practical advice aimed at minimizing our patients' risk of developing malignancy, whilst optimizing the benefits that thiopurines can provide.

Using adaptive model predictive control to customize maintenance therapy chemotherapeutic dosing for childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a common childhood cancer in which nearly one-quarter of patients experience a disease relapse. However, it has been shown that individualizing therapy for childhood ALL patients by adjusting doses based on the blood concentration of active drug metabolite could significantly improve treatment outcome. An adaptive model predictive control (MPC) strategy is presented in which maintenance therapy for childhood ALL is personalized using routine patient measurements of red blood cell mean corpuscular volume as a surrogate for the active drug metabolite concentration. A clinically relevant mathematical model is developed and used to describe the patient response to the chemotherapeutic drug 6-mercaptopurine, with some model parameters being patient-specific. During the course of treatment, the patient-specific parameters are adaptively identified using recurrent complete blood count measurements, which sufficiently constrain the patient parameter uncertainty to support customized adjustments of the drug dose. While this work represents only a first step toward a quantitative tool for clinical use, the simulated treatment results indicate that the proposed mathematical model and adaptive MPC approach could serve as valuable resources to the oncologist toward creating a personalized treatment strategy that is both safe and effective.

DNA incorporation of 6-thioguanine nucleotides during maintenance therapy of childhood acute lymphoblastic leukaemia and non-Hodgkin lymphoma

PURPOSE

To explore the DNA incorporation of 6-thioguanine nucleotide levels (DNA-6TGN) during 6-mercaptopurine (6MP) therapy of childhood acute lymphoblastic leukaemia (ALL) and non-Hodgkin lymphoma (NHL) and its relation to erythrocyte levels of their metabolites: 6-thioguanine-nucleotides (E-6TGN), methylated metabolites (E-MeMP), Methotrexate polyglutamates (E-MTX), and to thiopurine methyltransferase activity (TPMT).

METHODS

We studied these metabolites in 229 blood samples from 18 children with ALL (N = 16) or NHL (N = 2) on 6MP/Methotrexate maintenance therapy.

RESULTS

DNA-6TGN levels were significantly correlated to E-6TGN (r (p) = 0.66, p = 0.003) with a trend to reach a plateau at high E-6TGN levels. To explore the relative DNA incorporation of 6TGN in relation to cytosol 6TGN levels, a DNA-6TGN index was calculated as DNA-6TGN/E-6TGN. The DNA-6TGN index was inversely correlated to E-6TGN (r (p) = -0.58, p = 0.012), which implies that with increasing levels of E-6TGN relatively less 6TGN are incorporated into DNA. E-MeMP levels were correlated to the DNA-TGN index (r (p) = 0.60, p = 0.008), indicating that high levels of MeMP result in enhanced DNA-6TGN incorporation, possibly due to inhibition of purine de novo synthesis, mediated by some of the methylated 6MP metabolites.

CONCLUSIONS

DNA-6TGN may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than the previously used erythrocyte 6MP metabolites levels. Prospective clinical trials are needed to evaluate the usefulness of DNA-6TGN for individual dose adjustments.

Thiopurine methyltransferase genetics is not a major risk factor for secondary malignant neoplasms after treatment of childhood acute lymphoblastic leukemia on Berlin-Frankfurt-Münster protocols

Thiopurine methyltransferase (TPMT)is involved in the metabolism of thiopurines such as 6-mercaptopurine and 6-thioguanine. TPMT activity is significantly altered by genetics, and heterozygous and even more homozygous variant people reveal substiantially decreased TPMT activity. Treatment for childhood acute lymphoblastic leukemia (ALL) regularly includes the use of thiopurine drugs. Importantly, childhood ALL patients with low TPMT activity have been considered to be at increased risk of developing therapy-associated acute myeloid leukemia and brain tumors. In the present study, we genotyped 105 of 129 patients who developed a secondary malignant neoplasm after ALL treatment on 7 consecutive German Berlin-Frankfurt-Münster trials for all functionally relevant TPMT variants. Frequencies of TPMT variants were similarly distributed in secondary malignant neoplasm patients and the overall ALL patient population of 814 patients. Thus, TPMT does not play a major role in the etiology of secondary malignant neoplasm after treatment for childhood ALL, according to Berlin-Frankfurt-Münster strategies.

Methotrexate/6-mercaptopurine maintenance therapy influences the risk of a second malignant neoplasm after childhood acute lymphoblastic leukemia: results from the NOPHO ALL-92 study

Among 1614 children with acute lymphoblastic leukemia (ALL) treated with the Nordic Society for Paediatric Haematology and Oncology (NOPHO) ALL-92 protocol, 20 patients developed a second malignant neoplasm (SMN) with a cumulative risk of 1.6% at 12 years from the diagnosis of ALL. Nine of the 16 acute myeloid leukemias or myelodysplastic syndromes had monosomy 7 (n = 7) or 7q deletions (n = 2). In Cox multivariate analysis, longer duration of oral 6-mercaptopurine (6MP)/methotrexate (MTX) maintenance therapy (P = .02; longest for standard-risk patients) and presence of high hyperdiploidy (P = .07) were related to increased risk of SMN. Thiopurine methyltransferase (TPMT) methylates 6MP and its metabolites, and thus reduces cellular levels of cytotoxic 6-thioguanine nucleotides. Of 524 patients who had erythrocyte TPMT activity measured, the median TPMT activity in 9 patients developing an SMN was significantly lower than in the 515 that did not develop an SMN (median, 12.1 vs 18.1 IU/mL; P = .02). Among 427 TPMT wild-type patients for whom the 6MP dose was registered, those who developed SMN received higher average 6MP doses than the remaining patients (69.7 vs 60.4 mg/m2; P = .03). This study indicates that the duration and intensity of 6MP/MTX maintenance therapy of childhood ALL may influence the risk of SMNs in childhood ALL.

Thiopurine methyltransferase activity is related to the risk of relapse of childhood acute lymphoblastic leukemia: results from the NOPHO ALL-92 study

Myelotoxicity during thiopurine therapy is enhanced in patients, who because of single nucleotide polymorphisms have decreased activity of the enzyme thiopurine methyltransferase (TPMT) and thus more thiopurine converted into 6-thioguanine nucleotides. Of 601 children with acute lymphoblastic leukemia (ALL) who were treated by the NOPHO ALL-92 protocol, 117 had TPMT genotype determined, whereas for 484 patients only erythrocyte TPMT activity was available. The latter were classified as heterozygous, if TPMT activity was <14 IU/ml, or deficient (<1.0 IU/ml). 526 patients had TPMT wild type, 73 were presumed heterozygous, and two were TPMT deficient. Risk of relapse was higher for the 526 TPMT wild type patients than for the remaining 75 patients (18 vs 7%, P=0.03). In Cox multivariate regression analysis, sex (male worse; P=0.06), age (higher age worse, P=0.02), and TPMT activity (wild type worse; P=0.02) were related to risk of relapse. Despite a lower probability of relapse, patients in the low TPMT activity group did not have superior survival (P=0.82), possibly because of an excess of secondary cancers among these 75 patients (P=0.07). These data suggest that children with ALL and TPMT wild type might have their cure rate improved, if the pharmacokinetics/-dynamics of TPMT low-activity patients could be mimicked without a concurrent excessive risk of second cancers.

Pharmacogenetics influence treatment efficacy in childhood acute lymphoblastic leukemia

Pharmacogenetics covers the genetic variation affecting pharmacokinetics and pharmacodynamics, and their influence on drug-response phenotypes. The genetic variation includes an estimated 15 million single nucleotide polymorphisms (SNPs) and is a key determinator for the interindividual differences in treatment resistance and toxic side effects. As most childhood acute lymphoblastic leukemia treatment protocols include up to 13 different chemotherapeutic agents, the impact of individual SNPs has been difficult to evaluate. So far focus has mainly been on the widely used glucocorticosteroids, methotrexate, and thiopurines, or on metabolic pathways and transport mechanisms that are common to several drugs, such as the glutathione S-transferases. However, beyond the thiopurine methyltransferase polymorphisms, the candidate-gene approach has not established clear associations between polymorphisms and treatment response. In the future, high-throughput, low-cost, genetic platforms will allow screening of hundreds or thousands of targeted SNPs to give a combined gene-dosage effect (=individual SNP risk profile), which may allow pharmacogenetic-based individualization of treatment.

Host factors and consequence of chemotherapy in pediatric cancer patients

The 5-year survival rates for childhood ALL are approaching 80%, but therapy-related toxicities are common. One of the challenges in this population is determining the most efficacious therapeutic regimens for these individuals. Factors such as drug metabolism, genetics, and concomitant disease affect drug efficacy and may be important in determining therapeutic outcomes in these patients. This review will focus on these factors in the treatment of childhood ALL.

[Pharmacogenetics in oncology]

Pharmacogenetics studies the relationship between genetic polymorphisms and individual responses to drugs. In recent years, there has been a great progress in our knowledge of the effects of drug-metabolizing enzymes and molecular target genetic polymorfisms on cancer chemotherapy. Pharmacogenetics focuses on the prediction of drug efficacy and toxicity based on a patient's genetic profile with routinely applicable genetic tests to select the most appropriate medication at optimal doses for each individual patient. Two years ago the FDA approved one genetic test to detect patients with increased risk of severe toxicity associated with irinotecan therapy. There have also been commercialized genetic chips to genotyping two cytochrome P450 enzymes at the same time. Prospectively, stratifying patients based on genotype may identify subpopulations likely to experience severe toxicity or to derive benefit from a particular treatment strategy, helping us move toward the ultimate goal of individualized therapy. In this review, we describe the clinical effects of polymorphisms that may influence cancer chemotherapy.

Clinical pharmacogenetics in pediatric patients

Pediatric pharmacogenetic studies have the potential to improve the quality of medical care for children. The pediatric population presents a unique pharmacogenetic challenge as children have the additional complexity of ontological phenotypes that impact their drug response. Prescribing medications in children has historically been largely empirical, but utilization of pharmacogenetic information will allow pediatricians to gain key information regarding which patients are best suited for a particular therapeutic agent and which patients may be at risk for serious potentially life-threatening complications from standard treatment regimens. Although large, prospective, multisite investigators are still needed, we illustrate selective clinical examples of the pharmacogenetics for treatment of transplantation, asthma, leukemia and attention-deficit hyperactivity disorder in pediatric patients.

Azathioprine-associated acute myeloid leukemia in a patient with Crohn's disease and thiopurine S-methyltransferase deficiency

Immunosuppressive thiopurines like azathioprine, 6-mercaptopurine, and thioguanine are commonly used in inflammatory and neoplastic disorders. A subset of these patients are genetically slow metabolizers due to point-mutations in enzyme thiopurine S-methyltransferase (TPMT), and are at a higher risk of hematologic toxicity and leukemogenesis. We present such a patient who was a slow metabolizer for azathioprine, and developed a rapidly lethal form acute myeloid leukemia after relatively low dose exposure to the drug. There was prominent hemophagocytic activity in the bone marrow, and cytogenetic analysis showed a complex karyotype with monosomy 7, but no involvement of chromosome 8.

Thiopurines in current medical practice: molecular mechanisms and contributions to therapy-related cancer

Thiopurines have diverse clinical applications and their long-term use as anti-rejection drugs in transplant patients has been associated with a significantly increased risk of various types of cancer. Although they are slowly being replaced by a new generation of non-thiopurine immunosuppressants, it is anticipated that their use in the management of inflammatory and autoimmune diseases will continue to increase. Therapy-related cancer will remain a potential consequence of prolonged treatment for these generally non-life-threatening conditions. Understanding how thiopurines contribute to the development of cancer will facilitate clinical decisions about the potential risks to patients of long-term treatment for chronic inflammatory disorders.

Genome scan implicates adhesion biological pathways in secondary leukemia

The genetic risk factors for etoposide-induced leukemia with MLL translocations remain largely unknown. To identify genetic risk factors for and novel characteristics of secondary leukemia, we profiled 116,204 single nucleotide polymorphisms (SNPs) in germline and paired leukemic cell DNA from 13 secondary leukemia/myelodysplasia cases and germline DNA from 13 matched and 156 unmatched controls, all with acute lymphoblastic leukemia treated with etoposide. We analyzed global gene expression from a partially overlapping cohort. No single locus was altered in most cases. We discovered 81 regions of loss of heterozygosity (LOH) in leukemic blasts and 309 SNPs whose allele frequencies differed in cases vs controls. Candidate genes were prioritized on the basis of genes whose SNPs or expression differentiated cases from controls or showed LOH or copy number change in germline vs paired blast DNA from the 13 cases. Three biological pathways were altered: adhesion, Wnt signaling and regulation of actin. Validation experiments using a genome scan for etoposide-induced leukemogenic MLL chimeric fusions in 15 HapMap cell lines also implicated genes involved in adhesion, a process linked to de novo leukemogenesis. Independent clinical epidemiologic and in vitro genome-wide approaches converged to identify novel pathways that may contribute to therapy-induced leukemia.

Acute myeloid leukaemia secondary to treatment with capecitabine for metastatic colorectal cancer

A 63-year-old woman was diagnosed with acute myelo-monocytic leukaemia, associated with MLL gene rearrangement, 16 months after completion of oral capecitabine for metastatic colon cancer. Capecitabine, recommended for use in metastatic breast and colon cancer and more recently as adjuvant treatment of colon cancer, has not previously been reported to be associated with secondary cancer.