Co-Administration of Proton Pump Inhibitors May Negatively Affect the Outcome in Inflammatory Bowel Disease Treated with Vedolizumab.

Concomitant medications may alter the effect of biological therapy in inflammatory bowel disease. The aim was to investigate the effect of proton pump inhibitors on remission rates in patients with inflammatory bowel disease treated with the gut-selective vedolizumab. Patients from the Hungarian nationwide, multicenter vedolizumab cohort were selected for post hoc analysis. Primary outcomes were the assessment of clinical response and endoscopic and clinical remission at weeks 14 and 54. Secondary outcomes were the evaluation of the combined effect of concomitant steroid therapy and other factors, such as smoking, on remission. A total of 108 patients were identified with proton pump inhibitor data from 240 patients in the original cohort. Patients on steroids without proton pump inhibitors were more likely to have a clinical response at week 14 than patients on concomitant PPI (95% vs. 67%, p = 0.005). Non-smokers with IBD treated with VDZ were more likely to develop a clinical response at week 14 than smokers, particularly those not receiving PPI compared with patients on co-administered PPI therapy (81% vs. 53%, p = 0.041, and 92% vs. 74%, p = 0.029, respectively). We found that the use of PPIs in patients treated with VDZ may impair the achievement of response in certain subgroups. Unnecessary PPI prescriptions should be avoided.

Real-Life Efficacy of Tofacitinib in Various Situations in Ulcerative Colitis: A Retrospective Worldwide Multicenter Collaborative Study.

BACKGROUND AND AIMS: Tofacitinib (TFB) appears to be effective in the treatment of ulcerative colitis (UC); however, available real-world studies are limited by cohort size. TFB could be an option in the treatment of acute severe ulcerative colitis (ASUC). We aimed to investigate efficacy and safety of TFB in moderate-to-severe colitis and ASUC. METHODS: This retrospective, international cohort study enrolling UC patients with ≥6-week follow-up period was conducted from February 1 to July 31, 2022. Indications were categorized as ASUC and chronic activity (CA). Baseline demographic and clinical data were obtained. Steroid-free remission (SFR), colectomy, and safety data were analyzed. RESULTS: A total of 391 UC patients (median age 38 [interquartile range, 28-47] years; follow-up period 26 [interquartile range, 14-52] weeks) were included. A total of 27.1% received TFB in ASUC. SFR rates were 23.7% (ASUC: 26.0%, CA: 22.8%) at week 12 and 41.1% (ASUC: 34.2%, CA: 43.5%) at week 52. The baseline partial Mayo score (odds ratio [OR], 0.850; P = .006) was negatively associated with week 12 SFR, while biologic-naïve patients (OR, 2.078; P = .04) more likely achieved week 52 SFR. The colectomy rate at week 52 was higher in ASUC group (17.6% vs 5.7%; P < .001) and decreased with age (OR, 0.94; P = .013). A total of 67 adverse events were reported, and 17.9% resulted in cessation of TFB. One case of thromboembolic event was reported. CONCLUSIONS: TFB is effective in both studied indications. TFB treatment resulted in high rates of SFR in the short and long terms. Higher baseline disease activity and previous biological therapies decreased efficacy. No new adverse event signals were found.

Hungarian Linguistic, Cross-Cultural, and Age Adaptation of the Patient Satisfaction with Health Care in Inflammatory Bowel Disease Questionnaire (CACHE) and the Medication Adherence Report Scale (MARS).

BACKGROUND: The TRANS-IBD study examines the superiority of joint transition visits, with drug adherence and patient satisfaction among the outcome measures. Our aim was a cross-cultural, age- and disease-specific adaptation of the 'Medication Adherence Rating Scale' (MARS) and 'Patient satisfaction with health care in inflammatory bowel disease questionnaire' (CACHE) questionnaires in patients with inflammatory bowel disease (IBD). METHODS: Linguistic and cultural adaptation using test and re-test procedures were performed. Internal consistency with Cronbach's α coefficients, confirmatory factor analyses with root Mean Square Error of Approximation (RMSEA), Comparative Fit Index (CFI), and Tucker-Lewis Index (TLI) were determined. RESULTS: A total of 122 adolescents and 164 adults completed the questionnaires (47.5% male, mean age 17 ± 1; and 29.3% male, mean age 38 ± 11, respectively). In the MARS questionnaire, Cronbach's α scores were found good in adolescents (0.864) and acceptable in adults (0.790), while in the CACHE questionnaire, scores were rated as excellent in both populations (0.906 and 0.945, respectively). The test-retest reliabilities were satisfactory in both groups (MARS questionnaire: r = 0.814 and r = 0.780, CACHE questionnaire: r = 0.892 and r = 0.898, respectively). RMSEA showed poor fit values in the MARS questionnaire and reasonable fit values in the CAHCE questionnaire, CFI and TLI had statistically acceptable results. CONCLUSION: Age-and disease-specific Hungarian versions of the questionnaires were developed, which are appropriate tools for TRANS-IBD RCT and daily IBD care.

Non-medical switch from the originator to biosimilar and between biosimilars of adalimumab in inflammatory bowel disease - a prospective, multicentre study.

INTRODUCTION: Clinical data on the efficacy and safety of non-medical switch between adalimumab(ADA) biosimilars are limited. AIMS: The aim of this study was to evaluate medium-term clinical efficacy, drug sustainability and safety comparing non-medical switches from the originator to biosimilar ADA, and between ADA biosimilars. METHODS: 276 consecutive patients on maintenance ADA therapy (n = 205 Crohn's disease, n = 71 ulcerative colitis) were included. Data on clinical efficacy, biomarkers and adverse events were collected at four time points: 8-12 weeks prior switch, at baseline/switch, 8-12 weeks and 20-24 weeks after switch. Drug survival was evaluated after a median 40(IQR:35-42) weeks follow-up. RESULTS: A total 174 patients underwent a non-medical switch from the originator to a biosimilar, and 102 patients had a biosimilar-to-biosimilar switch. No significant difference was found in clinical remission rates at any time point in patients switching from originator to biosimilar(87.3%/88.5%/86.5%/85.7%) or biosimilar to biosimilar(74.5%/78.4%/85.3%/79.8%). Mean C-reactive protein levels remained unchanged in both cohorts(p = 0.856 and p = 0.525). Drug survival was similar between the two cohorts with a probability of 91.6%(SE: 2.2) and 87.0%(SE:3.4) to stay on drug after 40 weeks(log-rank:0.96; p = 0.327). Five cases of injection related adverse events were reported. CONCLUSION: Clinical benefit was sustained following non-medical switch from originator to biosimilar, or between biosimilars in adalimumab treated IBD patients.

Ustekinumab is associated with superior treatment persistence but not with higher remission rates versus vedolizumab in patients with refractory Crohn's disease: results from a multicentre cohort study.

Background: Treatment with antitumor necrosis factor alpha (anti-TNF-α) is safe and effective as first-line therapy; however, its efficacy is limited due to primary nonresponse (PNR) and secondary loss of response (LOR), resulting in treatment discontinuation in approximately 40%-50% of cases. Vedolizumab (VDZ) and ustekinumab (UST) therapies could be good alternatives in patient with anti-TNF failure; however, no head-to-head randomized comparison of these drugs as second- or third-line treatments has been made. Objectives: This study aimed to assess the treatment persistence and comparative effectiveness of UST and VDZ in patients with refractory Crohn's disease (CD). Design: In this nationwide retrospective study, patients with CD on UST or VDZ maintenance therapy were enrolled. Clinical data at baseline, after induction, and at week 52 were obtained. Methods: Clinical and biochemical activities as well as corticosteroid-free remission (SFR) rates were assessed, while concomitant medications, comorbidities, hospitalizations, and surgeries were recorded during the follow-up to detect any predictors. Results: A total of 161 UST- and 65 VDZ-treated patients completed the follow-up. No significant difference in clinical or biochemical remission rates was observed after induction between the two treatment groups; however, clinical remission rate at week 52 was higher in UST group. UST showed superior drug persistence than VDZ (86.5%, 57.9%, p < 0.0001). The drug type was predictive of clinical SFR at week 52 [p = 0.011, odds ratio (OR) = 2.39 with UST]. Drug failure rates were higher for VDZ than those for UST (PNR rates: 21.54% and 4.97%, respectively, p < 0.001, OR = 8.267, p = 0.001). LOR and escalations were more common during UST treatment (61.5% versus 36.9%, p < 0.001; 64.2% versus 23.1%, p < 0.001). Hospital and surgical admission rates did not differ significantly. Only one adverse event occurred with VDZ at week 20, which led to drug cessation. Conclusions: VDZ and UST were safe and effective for treating patients with CD in whom anti-TNF therapy failed. UST showed superior drug persistence than VDZ, but dose escalation was more frequent. Biologicals used in lower treatment lines resulted in better drug persistence.

Clinical efficacy, drug sustainability and serum drug levels in Crohn's disease patients treated with ustekinumab - A prospective, multicenter cohort from Hungary.

INTRODUCTION: Although efficacy of ustekinumab (UST) has been demonstrated through randomized trials, data from real-life prospective cohorts are still limited. Our aim was to evaluate clinical efficacy, drug sustainability, dose intensification and results from therapeutic drug monitoring in UST treated patients with Crohn's disease (CD) using a prospective, nationwide, multicenter cohort. METHODS: Patients from 10 Inflammatory Bowel Disease centers were enrolled between 2019 January and 2020 May. Patient demographics, disease phenotype, treatment history, clinical disease activity (Crohn's Disease Activity Index(CDAI), Harvey Bradshaw Index(HBI)), biomarkers, and serum drug levels were obtained. Evaluations were performed at week8 (post-induction), w16-20, w32-36, and w52-56 follow-up visits. RESULTS: A total of 142 patients were included [57.4% female; complex disease behavior (B2/B3):48%, previous anti-TNF exposition:97%]. Clinical response and remission rates after induction(w8) were 78.1% and 57.7% using CDAI, and 82.5% and 51.8% based on HBI scores. The one-year clinical remission rate was 58%/57.3%(CDAI/HBI). Composite clinical and biomarker remission (CDAI<150 and C-reactive protein<10 mg/L) rates were 35.4%; 33.3%; 38.6% and 36.6% at w8/w16-20/w32-36 and w52-56. Drug sustainability was 81.9%(standard deviation(SD): 3.4) at 1 year(1y). Probability of dose intensification was high and introduced early, 42.2%(SD:4.2) at ~w32 and 51.9%(SD:4.4%) at 1y. CONCLUSION: Ustekinumab showed favorable drug sustainability and clinical efficacy in a patient population with severe disease phenotype and previous anti-tumor necrosis factor (anti-TNF) failure, however frequent dose intensification was required.

Intravenous versus subcutaneous delivery of biotherapeutics in IBD: an expert's and patient's perspective.

Several biologic treatments are available in addition to intravenous also in subcutaneous form for treatment of chronic diseases. Benefits of the subcutaneous application of drugs include self-administration by the patient, shorter time of application process with less infusion related adverse events and consequently lower healthcare costs. With appropriate education and support patients are able to administer their treatments at home. This leads to improvement of quality of life, reduction of time needed to travel to the healthcare institution and consequently also reduces costs also for the patient.Over one million residents in the USA and 2.5 million in Europe are estimated to have inflammatory bowel disease (IBD), with substantial costs for health care. These estimates do not factor in the 'real' price of IBD, which can impede career aspirations, instil social stigma and impair quality of life in patients.The Virtual Community Meeting, which offered an exchange of experience and opinions from healthcare professionals who are active in treating IBD, and patients with this chronic disease, revealed in-depth arguments and answers to some essential questions: which patients prefer subcutaneous over intravenous dosing; which patients continue to favour intravenous infusions; what are the limitations regarding both applications; what is the patient's role in therapeutical decision-making and how does IBD affect the patient's work, finances and quality of life? The aim of this article is to discuss the differences between subcutaneous and intravenous dosing from the health-economic, scientific, and personal perspectives.The meeting offered strong confirmation that most of the patients and healthcare professionals prefer subcutaneous over intravenous drug administration but emphasise the management of risks associated with treatment compliance. Patient education provided by the IBD team in this regard is mandatory. Quality of life of patients is poorer during active disease, but the findings that it can improve over time, including as a result of home- or self-administration of biologics, may be encouraging for individuals with this chronic disease.

Management of acute gastrointestinal bleeding. Multidisciplinary guideline proposal. / Heveny gastrointestinalis vérzések ellátása. Multidiszciplináris útmutató javaslat.

Gastrointestinal bleeding has a profound impact on public health due to its high prevalence and severity. With the elderly population taking more anticoagulants/antiaggregants/non-steroid anti-inflammatory drugs, the digestive bleeding will certainly raise more and more challenges in quantity as well as in severity for the public healthcare system. The emergency medicine specialists and gastroenterologists have a central role in the management of patients presenting with gastrointestinal bleeding. In certain cases, radiologists, invasive radiologists, intensive care specialists and surgeons should also be involved in the decision making process and management of patients. Therefore, Hungarian experts felt the need to elaborate a comprehensive, multidisciplinary, practical local guideline reflecting the frequently arisen aspects based on current international guidelines. This guideline proposal covers topics of basic requirements, initial assessment of patients, risk evaluation, laboratory tests, hemodynamic resuscitation in the case of gastrointestinal bleeding followed by its consecutive steps of diagnosis and therapy sorted by location of the source of the hemorrhage. The authors give practical instructions for unsuccessful hemostasis or rebleeding. Finally, the role of surgery is also summarized in the management of gastrointestinal bleeding. Orv Hetil. 2020; 161(30): 1231-1242.

Real-life efficacy of vedolizumab on endoscopic healing in inflammatory bowel disease - A nationwide Hungarian cohort study.

Background: GEMINI trials demonstrated the therapeutic efficacy of vedolizumab (VDZ) in Crohn's disease (CD) and ulcerative colitis (UC).Research design and methods: Aim of this study was to determine the real-life effectiveness of VDZ on endoscopic healing in the Hungarian nationwide cohort of inflammatory bowel disease (IBD) patients based on the changes on clinical and endoscopic scores. Every adult IBD patient in the country (121 UC and 83 CD) who completed the short-term VDZ therapy was enrolled, of which 72 UC and 52 CD patients could complete the long-term therapy.Results: The rates of endoscopic healing were substantially higher in UC compared with CD patients during the short- and long-term therapy (52.9% vs. 21.7%, p < 0.0001, and 51.4% vs. 21.2%, p = 0.015, respectively). In CD, the rate of endoscopic healing was lower at week 14 compared with week 22 (14.5% vs. 37.0%, p = 0.026). Prior anti-TNF-α therapy (88.73%) was not associated with a significant decrease in therapeutic response. The average disease duration was significantly lower in CD patients achieving endoscopic healing at week 52 (11.75 vs. 5.27 years, p = 0.007).Conclusions: VDZ therapy is an effective therapeutic option in anti-TNF-α refractory IBD. However, the endoscopic healing rate was substantially lower and showed a significant delay in CD compared with UC.

Patient and general population values for luminal and perianal fistulising Crohn's disease health states.

BACKGROUND: In patients with Crohn's disease (CD), luminal disease activity paralleled by perianal fistulas may seriously impair health-related quality of life (HRQoL). Health utility values are not available from patients with CD that reflect the health loss associated with both luminal and perianal CD. OBJECTIVE: To generate utilities for luminal and concomitant perianal fistulising CD health states directly from patients and from members of the general public. METHODS: A cross-sectional survey was undertaken enrolling CD patients and a convenience sample of members of the general population. Respondents were asked to evaluate four common CD heath states [severe luminal disease (sCD), mild luminal disease (mCD), severe luminal disease with active perianal fistulas (sPFCD), and mild luminal disease with active perianal fistulas (mPFCD)] by 10-year time trade-off (TTO). In addition, patients assessed their current HRQoL by the TTO method. RESULTS: Responses of 206 patients (40.8% with perianal fistulas) and 221 members of the general population were analysed. Mean ± SD utilities among patients for sPFCD, sCD, mPFCD and mCD states were 0.69 ± 0.33, 0.73 ± 0.31, 0.80 ± 0.29 and 0.87 ± 0.26. Corresponding values in the general public were: 0.59 ± 0.31, 0.65 ± 0.29, 0.80 ± 0.26 and 0.88 ± 0.25. Patients with active perianal fistulas, previous non-resection surgeries, and higher pain intensity scores valued their current health as worse (p < 0.05). CONCLUSIONS: TTO is a feasible method to assess HRQoL in patients with perianal fistulising disease, often not captured by health status questionnaires. Utilities from this study are intended to support the optimization of treatment-related decision making in patients with luminal disease paralleled by active perianal fistulas.

Outcomes of Patients With Inflammatory Bowel Diseases Switched From Maintenance Therapy With a Biosimilar to Remicade.

BACKGROUND & AIMS: There is evidence that it is safe and effective for patients with inflammatory bowel diseases (IBD) to switch from maintenance therapy with an original infliximab drug to a biosimilar, but little is known about outcomes of reverse switches and/or multiple switches. We aimed to evaluate the effects of a reverse switch (from a biosimilar to Remicade) in a real-life cohort. METHODS: We performed a prospective observational study of 174 unselected and consecutive patients with IBD (136 with Crohn's disease [CD] and 38 with ulcerative colitis [UC]) who received maintenance therapy with the biosimilar in Hungary. In September 2017, patients were switched from the biosimilar (CT-P13) to Remicade, due to reimbursement policies. In our cohort, 8% (n = 14) patients had been previously exposed to the originator Remicade. We collected clinical and biochemical information from patients at baseline (time of the switch) and 16 and 24 weeks thereafter. Clinical remission was defined as a Crohn's disease activity index <150 points or no fistula drainage, or a partial Mayo score <3 points for patients with UC. Serum drug trough levels and anti-drug antibodies were measured at baseline and week 16. RESULTS: There was no significant difference in the proportion of patients in clinical remission at week 8 before the switch (82.5% with CD and 82.9% with UC), at baseline (80.6% with CD and 81.6% with UC), at week 16 (77.5% with CD and 83.7% with UC), or at week 24 (CD 76.3% with CD and 84.9% with UC) (P = .60 among groups for patients with CD and P = .98 among groups for patients with UC). For all patients, mean serum trough levels of infliximab were 5.33 ± 4.70 µg/mL at baseline and 5.69 ± 4.94 µg/mL at week 16 (P = .71); we did not find significant differences in prevalence of anti-drug antibody at baseline (16.2%) compared with week 16 (16.9%) (P = .87). Four infusion reactions occurred, until week 24 of follow up. There was no difference in outcomes or trough or antidrug antibody levels between patients with or without previous exposure to Remicade. CONCLUSIONS: We collected data from a real-life cohort of patients with CD or UC who were switched from maintenance therapy with a biosimilar to Remicade or were treated with only Remicade. No significant changes were observed in remission, trough levels, or antidrug antibodies in patients switched from the biosimilar to Remicade. No new safety signals were detected.

Presence and Effects of Pituitary Adenylate Cyclase Activating Polypeptide Under Physiological and Pathological Conditions in the Stomach.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide with widespread occurrence throughout the body including the gastrointestinal system. In the small and large intestine, effects of PACAP on cell proliferation, secretion, motility, gut immunology and blood flow, as well as its importance in bowel inflammatory reactions and cancer development have been shown and reviewed earlier. However, no current review is available on the actions of PACAP in the stomach in spite of numerous data published on the gastric presence and actions of the peptide. Therefore, the aim of the present review is to summarize currently available data on the distribution and effects of PACAP in the stomach. We review data on the localization of PACAP and its receptors in the stomach wall of various mammalian and non-mammalian species, we then give an overview on PACAP's effects on secretion of gastric acid and various hormones. Effects on cell proliferation, differentiation, blood flow and gastric motility are also reviewed. Finally, we outline PACAP's involvement and changes in various human pathological conditions.

[Introduction of a quality index in a Hungarian endoscopy unit]. / Minoségi indikátor bevezetése egy magyar gasztroenterológiai endoszkópos laboratórium munkájába.

UNLABELLED: The quality of endoscopic examinations substantially determines their value. In developed countries, Continuous Quality Management is used to improve it permanently. In Hungary there is no example for measuring quality in the field of gastrointestinal endoscopy. AIM: The measurement and improvement of quality of endoscopy applying completeness index (cecum intubation rate) during colonoscopy. PATIENTS AND METHODS: The authors defined base values retrospectively from 841 colonoscopy reports, performed in the last quarter of the year, before starting the project. The next two years (3160 colonoscopy in 2009 and 3167 in 2010) every three months they calculated the cecum intubation rate for each endoscopist. RESULTS: The cecum intubation rate was 81.6% in the base period. When the authors excluded examinations with poor preparations and those with a previously unknown stenosis that prevented the total colonoscopy, the adjusted cecal intubation rate was 90.9%. In the next 2 years, the cecum intubation rate was 84.2% and 85.7% (p = 0.0394), while adjusted cecum intubation rate proved to be 92.3% and 92.6% (p = 0.381 NS) for the whole endoscopy unit. Of the 14 endoscopists only 6 reached an adjusted cecum intubation rate of 90%, but in the second year of the project 10 of them reached this rate and only one endoscopist remained below 87%. The endoscopists performing more than 100 colonoscopies per year had better adjusted cecum intubation rate (base 91.2%; 92.7% and 93.1% during the 2 project years) compared to those with less than 100 colonoscopies per year (base, 86.7%; project period, 85.5 and 89%). CONCLUSIONS: The evaluation and publicity of the cecal intubation rate resulted in an improvement of the quality of colonoscopy. The authors also presented that endoscopists performing more than 100 colonoscopies per year have better endoscopic quality.

Functional evaluation of multidrug resistance transporter activity in surgical samples of solid tumors.

Determination of multidrug resistance (MDR) activity of tumor cells could provide important information for the personalized therapy of cancer patients. The functional calcein assay (MultiDrug Quant Assay, Solvo Biotechnology, Budaörs, Hungary) has been proven to be clinically valuable in hematological malignancies by determining the transporter activity of MDR protein 1 (MDR1, ATP-binding cassette protein [ABC] B1, P-glycoprotein-170) and MDR-related protein 1 (MRP1, ABCC1). In this study, we evaluated if the same functional test was adaptable for the analysis of MDR activity in solid tumors. For this purpose, tissue specimens of human colorectal cancer samples were subjected to limited enzymatic digestion by collagenase to provide a single-cell suspension; dead cells were excluded by 7-aminoactinomycin D staining, and epithelial cancer cells were detected by Cy5-conjugated anti-BerEP4 monoclonal antibody. The transporter functions of MDR1 and MRP1 in viable epithelial cells were assessed by flow cytometry detecting the intracellular accumulation of calcein dye after exposing cells to various MDR inhibitors. Collagenase disintegration preserved the MDR activity and the antigenicity of tumor cells. Thus using the extended calcein assay provided sufficient viable and functionally active tumor cells from surgical biopsies to determine the functional MDR activity. In conclusion, the newly described modified calcein assay may be applicable for evaluating the MDR phenotype in solid tissue specimens from colorectal forceps biopsy to surgical samples.

Early diagnosis of pancreatobiliary duct malignancies by brush cytology and biopsy.

Two hundred and five preoperative intraductal samplings (brushing and biopsy) were evaluated from 113 patients with biliary or Wirsung duct strictures. One hundred and three strictures could be specified by histology of the operative specimens, autopsy, or by the patients' clinical course. Preoperative diagnostic efficacy depended on the tumor location (it was the best for ampullary and para-papillary tumors), but the average quantitative indices for sensitivity, absolute sensitivity, specificity, positive and negative predictive values, diagnostic accuracy of cytology were 53%, 20%, 100%, 100%, 25%, 59%, respectively. The same values for biopsy were 43%, 34%, 100%, 100%, 36% and 56%. These figures improved after simultaneous cytology and biopsy. Close cooperation with the endoscopist was necessary in cases of negative, inconclusive and dysplastic (27%) samples. Repetition of sampling improved the results by 8%. Among the 26 preoperative false negative cases, sampling-, technical- and interpretative errors occurred in 84%, 4% and 12%, respectively. Revision of samples revealed 4 malignant cases among the false negative cytologic brushings. Reclassification of specimens considering the latest criteria - primary and secondary malignant features, pancreatic intraepithelial neoplasia (PanINs), etc. - resulted in improvement of the diagnostic efficiency.

Comparison of ELISA-based tyrosine kinase assays for screening EGFR inhibitors.

Receptor tyrosine kinases (PTKs) play key roles in the pathogenesis of numerous human diseases, including cancer, and therefore PTK inhibitors are currently under intense investigation as potential drug candidates. PTK inhibitor screening data are, however, poorly comparable because of the different assay technologies used. Here we report a comparison of ELISA-based assays for screening epidermal growth factor receptor (EGFR) tyrosine kinase (TK) inhibitory compound libraries to study interassay variations. All assays were based on the same protocol, except for the source of EGFR-TK enzymes. In the first protocol, the enzyme was isolated from A431 cells without affinity purification. In the second protocol, commercial EGFR-TK (Sigma) isolated from A431 cells by affinity-purification was employed. In the third protocol, an enzyme preparation obtained from a recombinant (Baculovirus transfected Sf9 cells) expression system was used. All assays employed the synthetic peptide substrate poly-(Glu,Tyr)l:4 and an ELISA-based system to detect phosphorylated tyrosine residues by a monoclonal antibody. We observed significant differences in both the activity of the enzymes and in the EGFR-TK inhibitory effect of our reference compound PD153035. The differences were significant in case of A431 cell lysate compared to affinity purified EGFR-TKs derived from either A431 cells or Baculovirus transfected Sf9 cells, whereas the latter two showed comparable results. Our data suggest that differences in terms of interassay variation are not related to the source of the enzyme but to its purity; changes in the mode of detection can markedly influence the reproducibility of results. In conclusion, normalization of the EGFR activity used for inhibitor screening and standardization of detection methods enable safe comparison of data.