CRISPR/Cas9-mediated homologous recombination in tobacco

KEY MESSAGE

Co-transformation of multiple T-DNA in a binary vector enabled CRISPR/Cas9-mediated HR in tobacco. HR occurred in a limited region around the gRNA target site. In this study, CRISPR/Cas9-mediated homologous recombination (HR) in tobacco (Nicotiana tabacum L. 'SR-1') was achieved using binary vectors comprising two (T1-T2) or three (T1-T2-T3) independent T-DNA regions. For HR donor with the tobacco acetolactate synthase gene, SuRB, T-DNA1 contained ΔSuRBW568L, which lacked the N-terminus region of SuRB and was created by three nucleotide substitutions (ATG to GCT; W568L), leading to herbicide chlorsulfuron (Cs) resistance, flanked by the hygromycin (Hm)-resistant gene. T-DNA2 consisted of the hSpCas9 gene and two gRNA inserts targeting SuRB and An2. For the 2nd HR donor with the tobacco An2 gene encoding a MYB transcription factor involved in anthocyanin biosynthesis, T-DNA3 had a 35S promoter-driven An2 gene lacking the 3rd exon resulting in anthocyanin accumulation after successful HR. After selecting for Hm and Cs resistance from among the 7462 Agrobacterium-inoculated explants, 77 independent lines were obtained. Among them, the ATG to GCT substitution of endogenous SuRB was detected in eight T1-T2-derived lines and two T1-T2-T3-derived lines. Of these mutations, four T1-T2-derived lines were bi-allelic. All the HR events occurred across the endogenous SuRB and 5' homology arm of the randomly integrated T-DNA1. HR of the SuRB paralog, SuRA, was also found in one of the T1-T2-derived lines. Sequence analysis of its SuRA-targeted region indicated that the HR occurred in a limited (< 153 bp) region around the gRNA target site. Even though some T1-T2-T3-derived lines introduced three different T-DNAs and modified the An2 gRNA target site, no signs of HR in the endogenous An2 could be observed.

Abstract P6-01-02: Machine learning-based structural analysis and oxygen saturation measurement of tumor-associated vessels in breast cancer using a photoacoustic tomography system

Introduction

Breast cancer induces angiogenesis, one of the primary factors responsible for tumor progression. Therefore, the ability to visualize angiogenesis at a higher resolution is crucial. Photoacoustic tomography is a noninvasive method of visualizing angiogenesis involving light absorption and ultrasonic wave emission. If the irradiation light wavelength is adjusted for hemoglobin, vascular imaging is possible. Furthermore, using two wavelengths for oxidized and reduced hemoglobin, “S-factor,” can be calculated, which nearly corresponds to oxygen saturation. Therefore, photoacoustic imaging allows the assessment of breast lesions from vascular structural and functional viewpoints.

Objectives

This study aimed to demonstrate the possible utility of photoacoustic tomography for clinical application focusing on the morphologic features and oxygen saturation status of breast tumor-related vessels.

Methods

For the morphological analysis, we applied a machine learning-based method for automatic vessel extraction, and for the functional analysis we evaluated hemoglobin oxygen saturation calculating signals obtained at two wavelengths. In our system, a 3D ultrasound image was simultaneously acquired as a volume image of a tumor, which helped analyze the positional relationship between the vessels and the tumor.

Results

On morphological analysis, the fine structure of tumor-related vessels was rendered in high resolution. In our system, the blood vessels branched toward the tumor 2-3 more times more frequently than observed on contrast-enhanced MRI, illustrating a finer level of blood vessels near the tumor on our system than on MRI. Next, we analyzed the six morphologic features of vessels (radius, volume, curvature, contraction, maximum angle and vessel branch number) that are associated with the pathologic condition in neuroscience. We determined that the feature distribution of vessels located close to the tumor differed from that located away from the tumor. For example, vessels near the tumor had higher curvature, which means they are more tortuous than healthy vessels. The difference in the distribution of all six features was statistically significant on the Kolmogorov-Smirnov test.

On functional analysis, S-factor measurement of the healthy human breast demonstrated clearly demarcated arteries and veins. The S-factor of any artery was nearly 100%, while that of the veins inside the breast cancer tended to be a little higher (approximately 5%) compared to that in the healthy part. This tendency of veins was not recognized in benign tumors. This could show arteriovenous shunt in cancer microenvironment. We found low saturation signals emerging in the tumor tissue following bevacizumab-containing chemotherapy, indicating the possibility that our system reveals microenvironment changes.

Discussion

If our system can identify the structure or oxygen saturation characteristics unique to tumor-associated vasculature, it could contribute to the improved accuracy of breast cancer diagnosis and allow the observation of tumor vessel normalization because of the drug treatment. An earlier grasp of the therapeutic effect could lead to the provision of individualized medicine.

Citation Format: Matsumoto Y, Gu L, Bise R, Asao Y, Sekiguchi H, Yoshikawa A, Ishii T, Takada M, Kataoka M, Sakurai T, Yagi T, Sato I, Togashi K, Shiina T, Toi M. Machine learning-based structural analysis and oxygen saturation measurement of tumor-associated vessels in breast cancer using a photoacoustic tomography system [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-01-02.

An analysis of factors associated with compliance and dropout of sublingual immunotherapy on Japanese cedar pollinosis patients

BACKGROUND

Sublingual immunotherapy (SLIT) is safe and effective but compliance is problematic. In this study we evaluated dropout and compliance among adults (≥20 years of age) and adolescents (<20 years of age) for Japanese cedar pollen extract (JCPE), an aqueous SLIT approved in 2014 in Japan.

METHODS

Administrative claims data on 1236 Japanese patients, 846 adults (mean age, 43.0 years; 41.8% female) and 249 adolescents (mean age, 14.1 years; 36.6% female), with a JCPE prescription between October 2014 and June 2016 were reviewed. Adults and adolescents were divided according to the year they started SLIT (1- and 2-year cohorts) to calculate dropout and compliance and identify associated factors using multivariate Cox and linear regression models.

RESULTS

In 1- and 2-year adult cohorts, dropout rates were 13.5% and 22.1% and compliance rates were 92.8% and 88.8%, respectively. Adolescents had higher dropout and lower compliance. Patients 40-59 years of age had a lower dropout risk than patients 20-29 years of age. Dropout hazard ratios (95% confidence interval) in 1- and 2-year cohorts were 0.26 (0.12-0.58) and 0.40 (0.17-0.93) in patients 40-49 years of age and 0.32 (0.14-0.75) and 0.35 (0.13-0.92) in patients 50-59 years of age, respectively. Younger age contributed to lower compliance in 1- and 2-year adult cohorts (p = 0.001 and p = 0.02, respectively). Systemic steroidal medication history and male gender were positively associated with compliance in adults but not in adolescents.

CONCLUSION

High dropout rate was associated with younger generations. Compliance in adults, but not in adolescents, was associated with age, systemic steroidal medication history, and gender.

The rate and treatment outcome of thiamine deficiency in cancer patients diagnosed with delirium: A preliminary study

205

Background: Vitamin B1 is essential for life, but cannot be synthesized in vivo and must be ingested from outside the body. Retention in the body is as short as 18 days, so that long-term appetite loss can easily lead to vitamin B1 deficiency, resulting in a condition known as Wernicke's encephalopathy (WE), which is characterized by disturbed consciousness, ataxia, and ocular movement disorders. Early detection and treatment with intravenous vitamin B1 usually results in recovery without sequelae, while a delay in detection can lead to severe brain damage (Korsakoff syndrome). The mortality rate is approximately 20%. Recent studies have shown that cancer patients may also experience thiamine deficiency and WE. WE is often overlooked as the typical symptoms are nonspecific, and some cases do not exhibit the disturbed consciousness characteristic of WE. Clinical awareness can be improved by confirming the actual rate and clarifying the associated symptoms, leading to more accurate WE diagnosis. Methods: We retrospectively examined the medical records for patients admitted to Saitama Medical University International Medical Center between 1 October 2014 and 31 May 2018 with cancer as the main disease who consulted the Psycho-oncology Department and were diagnosed with delirium by a psychiatrist. Patient background, medical treatment, neurological symptoms, blood biochemical findings, and disease course after vitamin B1 administration were examined. This study was approved by the IRB of this institution (Approval No. 18-080). Results: Eligibility criteria were met by 76 of 126 patients who received consultations during the study period, with 32 (43%) having a vitamin B1 deficiency. Vitamin B1 treatment led to a full recovery in 19 (59%) of these 32 patients. Conclusions: Our results show that the rate vitamin B1 deficiency in patients in this study was high, although >50% of the affected patients recovered with treatment. This indicated that it is necessary to pay close attention to vitamin B1 deficiency in cancer patients with psychiatric symptoms, and future study is planned to clarify the factors involved in the onset of vitamin B1 deficiency.

A descriptive epidemiological study on the treatment options for head and neck cancer: Transition before and after approval of cetuximab

PURPOSE

Chemoradiotherapy is among the effective treatment modalities for head and neck cancer (HNC). We aimed to elucidate the factors affecting drug selection by describing the actual situation of chemoradiotherapy for HNC in Japan and the transition in treatment selection before and after the approval of cetuximab.

METHOD

We used a claims database involving multiple hospitals nationwide. The study included patients diagnosed with HNC between April 2008 and August 2015 who underwent chemoradiotherapy. The anticancer drugs used were categorized into four groups, namely, cetuximab, cisplatin, other platinum agents, and other agents. After assessing patient background and transition in concomitant drugs, we performed multinomial logistic regression analysis to determine factors that affect patient drug selection.

RESULTS

This study analyzed 2777 patients whose median age was 66 years. A cisplatin-based regimen remained the most commonly used concomitant drug even after cetuximab approval. In multinomial logistic regression analysis, the odds ratio and 95% confidence interval (CI) in terms of age (66 y or older vs less than 65 y) relative to the cisplatin group were 3.01 (95% CI, 2.26-4.02) for the cetuximab group; 1.76 (95% CI, 1.22-2.48) for the other platinum agent group; and 3.09 (95% CI, 2.39-3.99) for the other agent group.

CONCLUSION

This study showed the current practices in concomitant medication used in chemoradiotherapy for HNC patients in Japan, the transition in anticancer drugs used before and after cetuximab approval, and the factors affecting the selection of concomitant drugs.

Prescription of Antidementia Drugs and Antipsychotics for Elderly Patients in Japan: A Descriptive Study Using Pharmacy Prescription Data

BACKGROUND

Antipsychotics are commonly used for managing behavioral and psychological symptoms of dementia among elderly patients with dementia receiving antidementia drugs (ADDs). However, the use of antipsychotics among these patients has not been investigated since 3 ADDs were approved in 2011 in Japan.

METHOD

We conducted a descriptive study using pharmacy prescription data and identified patients aged ≥65 years who were newly prescribed donepezil, memantine, rivastigmine, and galantamine between January 1, 2012, and September 30, 2014. We determined the proportion of antipsychotic prescription and the factors affecting antipsychotic prescription using multivariable Cox proportional hazard models.

RESULT

Of 13 876 patients, 1705 were memantine users, and the proportion of antipsychotic prescription among them was the highest (11.1%). Adjusted hazard ratios for donepezil, rivastigmine, and galantamine were 0.66, 0.56, and 0.66, respectively, relative to that for memantine.

CONCLUSION

Compared to other ADD users, new memantine users were most likely to be prescribed antipsychotics.

Influence of comorbidities on the implementation of the fundus examination in patients with newly diagnosed type 2 diabetes

AIMS

To investigate the influence of comorbidities on undergoing a diabetic eye examination in patients with newly diagnosed type 2 diabetes mellitus (T2DM).

DESIGN

Retrospective cohort study METHODS: This was a retrospective cohort study using data from health insurance claims made between January 2005 and March 2013 in Japan. The primary outcome was implementation of the fundus examination that includes fundus photography, ophthalmoscopy and optical coherence tomography by a doctor within one year of initial drug therapy for Type2 Diabetes Mellitus (T2DM). We used multivariable logistic regression models with adjustment for demographic parameters to investigate the influence of comorbidities (hypertension and/or hyperlipidemia) on patients with T2DM receiving fundus examinations. We conducted an additional analysis to investigate whether the site of treatment might influence the performance of fundus examinations in patients with T2DM.

RESULTS

A total of 6,492 patients were eligible for this analysis, of which 1,044 (16.1%) had comorbidities and 2,212 (34.1%) received the fundus examination. In the multivariable analysis, there was a significant association between comorbidities and a lower proportion of examination implementation (odds ratio [OR], 0.57; 95% confidence interval [CI], 0.48-0.68; P<0.001). The implementation proportion for patients treated for comorbidities and T2DM in the same facility was also low (OR, 0.52; 95% CI, 0.43-0.63; P<0.001).

CONCLUSIONS

These results suggest that the proportion of taking fundus examination is low among patients with comorbidities, especially in patients treated at the same facility for comorbidities and T2DM. This may help to increase the proportion of T2DM patients receiving fundus examinations.

Population-based incidence of diabetic ketoacidosis in type 2 diabetes: medical claims data analysis in Japan

PURPOSE

Determination of the incidence rate of diabetic ketoacidosis (DKA) in type 2 diabetes mellitus (T2DM) is urgent, in response to the safety issue with use of the glucose lowering drugs, sodium-glucose cotransporter-2 inhibitors, and DKA.

METHODS

We extracted data of adult patients with T2DM from a medical claims database in Japan, which included 1 million individuals. The study period was 2005-2013, before the era of sodium-glucose cotransporter-2 inhibitors. The inclusion criteria were patients with a diagnosis of T2DM who had at least 1 prescription for a glucose-lowering drug. We further examined the number of DKA-related admissions and medication use prior to admission. Calculation of DKA incidence was on a patient-years basis, with 95% confidence interval using a Poisson distribution.

RESULTS

Of 36,674 adult patients with T2DM, we identified 74 cases admitted for DKA, with an estimated DKA incidence of 0.48/1000 (95% confidence interval, 0.38-0.60/1000) patient-years. Of these 74 cases, approximately two-thirds of patients had no past or recent history of glucose-lowering drug use before admission for DKA.

CONCLUSIONS

This study estimated that the incidence of DKA was 0.48/1000 patient-years in Japan, similar to previous studies. We also found that underuse of glucose-lowering medication was common among patients hospitalized for DKA. KEY POINTS The population-based incidence of DKA in T2DM is largely unknown. In Japan, the estimated DKA incidence was 0.48/1000 (95% CI, 0.38-0.60/1000) patient-years. Drug-induced DKA is an emerging research area, and our results can be applied to evaluating the risk of DKA.

A case of iatrogenic pneumothorax in which chest tube placement could be avoided by intraoperative evaluation with transthoracic ultrasonography

We report a case of iatrogenic pneumothorax in which chest tube placement was avoided by continuous intraoperative evaluation with transthoracic ultrasonography. A 53-year-old man had undergone a subsegmentectomy. While attempting to place a central venous catheter in the right internal jugular vein after the induction of anesthesia, we identified gas absorption during the puncture and suspected a pneumothorax. Chest X-ray revealed an ~5-mm collapse of the right lung apex. Tension pneumothorax was a concern during surgery because of the long-term positive pressure ventilation, but we decided to start the operation without preventative chest tube placement. During the operation, we regularly observed the midclavicular line of the second intercostal space using ultrasound. The operation was completed uneventfully. In this case, we effectively utilized ultrasound and avoided preventive chest tube placement and the associated complications. Transthoracic ultrasonography could be performed easily and continuously during surgery and was effective for evaluating the progression of an intraoperative pneumothorax.

International trends in clozapine use: a study in 17 countries

OBJECTIVE

There is some evidence that clozapine is significantly underutilised. Also, clozapine use is thought to vary by country, but so far no international study has assessed trends in clozapine prescribing. Therefore, this study aimed to assess clozapine use trends on an international scale, using standardised criteria for data analysis.

METHOD

A repeated cross-sectional design was applied to data extracts (2005-2014) from 17 countries worldwide.

RESULTS

In 2014, overall clozapine use prevalence was greatest in Finland (189.2/100 000 persons) and in New Zealand (116.3/100 000), and lowest in the Japanese cohort (0.6/100 000), and in the privately insured US cohort (14.0/100 000). From 2005 to 2014, clozapine use increased in almost all studied countries (relative increase: 7.8-197.2%). In most countries, clozapine use was highest in 40-59-year-olds (range: 0.6/100 000 (Japan) to 344.8/100 000 (Finland)). In youths (10-19 years), clozapine use was highest in Finland (24.7/100 000) and in the publicly insured US cohort (15.5/100 000).

CONCLUSION

While clozapine use has increased in most studied countries over recent years, clozapine is still underutilised in many countries, with clozapine utilisation patterns differing significantly between countries. Future research should address the implementation of interventions designed to facilitate increased clozapine utilisation.

Diabetes mellitus and risk of early-onset Alzheimer's disease: a population-based case-control study

BACKGROUND AND PURPOSE

Previous studies have reported that diabetes is a risk factor for both all-cause and vascular dementia; however, diabetes as a risk factor for Alzheimer's disease (AD) remains controversial. Therefore, the aim was to elucidate the association between diabetes and early-onset AD.

METHODS

A case-control study was conducted using a population-based database that included medical and pharmacy claims and insurance eligibility data, from beneficiaries of corporate employees and their dependent family members. Cases were aged 40-64 years and were first prescribed medications for AD between 2005 and 2016. Up to four controls matched for age, sex and hospital type were included for each case. Data were analyzed using conditional logistic regression and compared between the sexes.

RESULTS

Data from 371 patients with AD (mean age 56.3 ± 5.3 years; 48% female) and 1484 controls were analyzed. Use of antidepressants, antipsychotics and antithrombotics during the index month was higher amongst patients with AD (19.4%, 34.5% and 11.3%, respectively) than amongst controls (2.9%, 10.3% and 7.3%, respectively). Our findings suggest no evidence for an association between diabetes and risk of early-onset AD (adjusted odds ratio 1.31; 95% confidence interval 0.90-1.92). In the subgroup analyses, adjusted odds ratios in patients with diabetes were 0.73 (95% confidence interval 0.38-1.39) and 1.68 (95% confidence interval 1.06-2.67) for female and male patients, respectively.

CONCLUSIONS

There is no apparent association between diabetes and risk of early-onset AD in the total study population, although a weak association was observed amongst male patients.

Predictive factors for the placebo effect in clinical trials for dry eye: a pooled analysis of three clinical trials

BACKGROUND

Placebo effect is one of the methodological difficulties in dry eye clinical trials. If we could elucidate the tendencies of the placebo response and find predictors, we could reduce the placebo response in clinical trials for dry eye. In this study, we investigated the predictive factors for the placebo effect in dry eye clinical trials.

METHODS

A total of 205 patients with dry eye assigned to the placebo arms of three placebo-controlled randomised clinical trials were analysed by simple and multivariable regression analysis. The corneal fluorescein (FL) staining score and dry eye symptoms were studied at week 4. The variables of interest included gender, age, complications of Sjögren's syndrome, Schirmer's test I value, tear break-up time and conjunctival hyperaemia score. We also conducted a stratified analysis according to the patients' age.

RESULTS

Among all the studied endpoints, the baseline scores were significantly related to the corresponding placebo response. In addition, for the FL score and the dryness score, age was a significant predictor of the placebo response (p=0.04 and p<0.0001, respectively). Stratified analysis by age showed that patients more than 40 years of age are more likely to have a stronger placebo response in the FL and dryness scores.

CONCLUSION

The baseline scores and age were predictive factors of the placebo response in frequently used endpoints, such as FL score or dryness symptoms. These patient characteristics can be controlled by study design, and our findings enable the design of more efficient placebo-controlled studies with good statistical power.

Trends in antipsychotic prescriptions for Japanese outpatients during 2006-2012: a descriptive epidemiological study

PURPOSE

This study aimed to assess the trends in antipsychotic prescriptions for outpatients in Japan, where a community-based approach to mental healthcare is emphasized.

METHODS

This descriptive epidemiological study used claims data from 1038 community pharmacies across Japan. Outpatients who were ≥18 years old and receiving their initial antipsychotic prescription during 2006-2012 were evaluated. The annual trends were reported for monotherapies, polypharmacy, antipsychotic doses, and the concurrent prescription of psychotropic medications.

RESULTS

The 152 592 outpatients included 101 133 (66%) adults (18-64 years old) and 51 459 (34%) older adults (≥65 years old). Among the adults, second-generation antipsychotic monotherapy prescriptions increased from 49% in 2006 to 71% in 2012, first-generation antipsychotic monotherapy prescriptions decreased from 29 to 14%, and antipsychotic polypharmacy decreased from 23 to 15%, respectively. Among the older adults, second-generation antipsychotic monotherapy prescriptions increased from 64 to 82%, first-generation antipsychotic monotherapy prescriptions decreased from 29 to 12%, and antipsychotic polypharmacy decreased from 7 to 6%, respectively. During the study period, >80% of the adults and >90% of the older adults received antipsychotics at risperidone-equivalent doses of <6 mg/day. Anxiolytics/hypnotics, antidepressants, antiparkinson agents, mood stabilizers, and anti-dementia agents were concurrently prescribed with antipsychotics for 70, 33, 20, 20, and 0.3% of the adults and for 43, 16, 19, 8, and 16% of the older adults, respectively.

CONCLUSIONS

The present study evaluated large-scale claims-based datasets and found that high-dose prescriptions and antipsychotic polypharmacy among Japanese outpatients were not as prevalent as has been previously thought. Copyright © 2017 John Wiley & Sons, Ltd.

Change in the structure and function of lectin by photodissociation of NO

We have shown here that the structure and sugar-binding activity of lectin can be changed by the photodissociation of NO.

Eccrine porocarcinoma of the vulva: a case report and review of the literature

Background

Malignant tumors arising from the vulva account for only 0.6 % of all cancers in female patients. The predominant histologic type, representing about 90 % of these malignancies, is squamous cell carcinoma. Eccrine porocarcinoma is a rare malignant tumor arising from sweat glands. The incidence of eccrine porocarcinoma is estimated at 0.005–0.01 % of all cutaneous tumors. To the best of our knowledge, only seven previous cases of vulvar eccrine porocarcinoma have been reported in the English-language literature. We present the case of a patient with eccrine porocarcinoma of the vulva, and we summarize the clinical features of this disease using seven previously reported cases.

Case presentation

A 54-year-old Japanese woman visited a local hospital complaining of fever and left vulvar pain for 2 months. An initial examination revealed a 1 × 1 cm, firm, ulcerative mass in the inner aspect of the left labium minorum. With a preoperative diagnosis of vulvar squamous cell carcinoma, we performed a radical local excision followed by bilateral inguinal lymphadenectomy. Histological examination showed eccrine porocarcinoma, stage IB (T1bN0M0). Radiation therapy with weekly cisplatin administration was then given as adjuvant therapy. One month after treatment was completed, computed tomography revealed multiple metastases in the bilateral lungs and in the sacral bone. The patient received three courses of chemotherapy (paclitaxel and carboplatin) and underwent palliative radiation therapy to the sacrum. She died of her disease 12 months after surgery.

Conclusions

We report the case of a patient with eccrine porocarcinoma of the vulva and summarize the clinical features and the treatment options of eccrine porocarcinoma from a few retrospective case reports. Although eccrine porocarcinoma is a rare disease, clinicians and pathologists should be aware of its clinical and histological features and its biological behavior.

Comparison of the Safety Profiles of Pegylated Interferon α-2a and α-2b Administered in Combination with Ribavirin for Chronic Hepatitis C Infection: A Real-World Retrospective Cohort Study

This study compares the safety profiles of pegylated interferon (PEG-IFN) α-2a and α-2b administered in combination with ribavirin, based on the variable of time to withdrawal from treatment due to adverse events. We conducted a real-world retrospective cohort study using the Japanese interferon database. Based on eligibility criteria, individuals with chronic hepatitis C virus (HCV) infection were identified in the database covering the period December 2009 to August 2015. The primary outcome measure was defined as difference in time to withdrawal from treatment due to adverse events between patients receiving PEG-IFN α-2a combined with ribavirin and those receiving PEG-IFN α-2b combined with ribavirin. The difference was analyzed using the multivariate Cox proportional hazards regression model. A frailty model was also applied to consider regional (prefectural) variation. After eligibility evaluation, 11058 individuals were included in the analysis. 3774 were treated with PEG-IFN α-2a, and 6764 with PEG-IFN α-2b, with 11.84 and 12.30% respectively withdrawing from treatment due to adverse events. The Cox model showed no significant difference between the two groups (hazard ratio (HR), 95%CI; 0.918, 0.817 to 1.031; p=0.1475). The results were consistent even when regional variation and other confounding variables were adjusted in the frailty model. In conclusion, there may be no difference in time to withdrawal from treatment due to adverse events between PEG-IFN α-2a and PEG-IFN α-2b combined with ribavirin. Applying the method used here to future studies using novel treatment regimens may also provide important information for the treatment of chronic HCV infection in clinical practice.