Human herpesvirus 6 in biopsies from patients with gastrointestinal symptoms after allogeneic stem cell transplantation.

Gastrointestinal complications are frequent after allogeneic stem cell transplantation (allo-SCT). Main differential diagnoses are graft-versus-host disease (GvHD) and viral infections. In this retrospective analysis, we included 50 patients with severe vomiting or diarrhea in the first year after allo-SCT. One hundred two biopsies obtained by colonoscopy or endoscopy of the upper gastrointestinal tract were analysed by conventional histology for signs of GvHD and by qualitative polymerase chain reaction (PCR) for viral DNA of human herpesvirus 6 (HHV-6) and other virus of the herpes family. DNA of HHV-6 was detected in 38 of 75 initial samples (51%) and in 19 of 27 follow-up biopsies (70%). In the initial samples (n = 75), HHV-6 DNA was detected in 20/37 (54%) biopsies in the presence of GvHD compared to 18/38 (47%) biopsies without signs of GvHD. At the time of the first endoscopic investigation, most patients received antiviral prophylaxis with aciclovir. None of the follow-up biopsies was HHV-6 DNA negative after antiviral treatment with aciclovir, foscarnet or ganciclovir. By univariate analysis, no risk factor for HHV-6 detection could be demonstrated. In this cohort of patients with severe gastrointestinal complications, there was no significant difference in the overall survival between patients with or without HHV-6 DNA detection in the gastrointestinal tract. In summary, the detection of HHV-6 DNA had no impact on overall survival. Moreover, antiviral therapy against HHV-6 was without effect. Thus, positive PCR results in GI tract samples do not necessarily reflect reactivation of HHV-6. Further studies are needed to define the significance of HHV-6 for GI tract symptoms after allo-SCT.

Differentiation between benign and malignant adrenal mass using contrast-enhanced ultrasound.

PURPOSE: Adrenal masses can be detected by ultrasound with high sensitivity and specificity. The aim of the present study was to evaluate CEUS in a large patient population using CEUS patterns identified in a previous pilot study. MATERIALS AND METHODS: 116 adrenal masses were evaluated by ultrasound, including CEUS with the contrast agent Sonovue®. The dynamic of contrast enhancement (CE) was analyzed using time-intensity curves. The time of the first CE in the adrenal mass was used to define four CEUS patterns: pattern I = early arterial CE, pattern II = arterial CE, pattern III = late CE, pattern IV = no CE. In addition, all patients received CT/MRI and hormonal testing. In suspicious cases biopsy or adrenalectomy was performed. RESULTS: CEUS patterns I&II were seen in all patients with primary or secondary malignant lesions of the adrenal gland (n = 16). The sensitivity and specificity of CEUS for the diagnosis of malignant adrenal mass were 100 % (CI [75;100]) and 67 % (CI [56;75]), respectively. Overall histology was available as a reference method for 40 adrenal masses. In 68 % of histologically diagnosed adrenal masses, MRI/CT and CEUS were congruent concerning the characterization of malignant versus benign adrenal mass. CONCLUSION: Contrast-enhanced ultrasound may be a useful method in the diagnostic work-up of adrenal mass with excellent sensitivity for the diagnosis of malignancy.

Trends in the postmortem epidemiology of invasive fungal infections at a university hospital.

BACKGROUND: Due to the continuing lack of sensitive and specific diagnostic tools, clinical data on opportunistic invasive fungal infections (IFIs) remain difficult to assess and postmortem data are indispensable to monitor trends in frequency and disease patterns. METHODS: Following-up on our previous report covering the period between 1978 and 1992, all protocols of postmortems performed between 1993 and 2005 at the University Hospital of Frankfurt/Main were retrospectively screened for the presence of IFIs. RESULTS: The analysis of 2707 consecutive autopsies identified 221 patients with IFIs (mean age, 52 years; range, 10 days-94 years). The prevalence of IFIs at autopsy steadily increased over the analyzed time periods (from 6.6% in 1993-1996 to 10.4% in 2001-2005), continuing the trend that was observed at our institution before. The increasing prevalence of IFIs was mainly due to an increase in Candida infections; rates of infections caused by Aspergillus, Cryptococcus, Zygomycetes and Pneumocystis remained constant. However, Aspergillus remained the leading pathogen. Patients with hematologic malignancies had the highest frequency of IFIs at postmortem. Candida most commonly affected the gastrointestinal tract, whereas Aspergillus most commonly affected the lung. CONCLUSIONS: The results of this analysis show continuing and relevant changes in the epidemiology of IFIs over time. Despite the expanding antifungal armamentarium, IFIs infections remain an important cause of morbidity and mortality in severely ill hospitalized patients.

Real-time elastography and contrast-enhanced ultrasound for the assessment of thyroid nodules.

OBJECTIVE: Work-up of thyroid nodules remains challenging. Recent technologies enable determination of tissue elasticity and perfusion using ultrasound devices. The aim of the present study was to evaluate real-time elastography (RTE) and contrast-enhanced ultrasound with Sonovue (CEUS) for the differentiation of benign and malignant thyroid nodules. MATERIALS AND METHODS: Inclusion criteria were: nodules ≥1 cm, non-functioning or hypo-functioning on radionuclide scanning, and cytological/histological assessment. All patients received conventional ultrasound, RTE and CEUS. RTE was classified as: Elasticity-Score (ES)1 = soft, ES2 = predominantly soft, ES3 = predominantly hard, ES4 = hard nodule. CEUS-video clips were digitally recorded and analyzed using time-intensity-curves within selected regions-of-interest. RESULTS: Fifty-three nodules in 50 patients were available for analysis. Forty-six nodules were benign on cytology/histology, 6 nodules were papillary carcinoma and one nodule was a follicular carcinoma. Nodule margin irregularity was the ultrasound pattern most predictive of malignancy with sensitivity 57% (95% confidence interval: 18-90%) and specificity 85% (71-94% p<0.05). When using ES3&4 for the diagnosis of malignant nodules sensitivity and specificity were 86% (42-99.7%) and 87% (75-95%), respectively (p = 0.0003). The only malignant nodule missed with RTE was a follicular carcinoma. Sensitivity for the diagnosis of papillary carcinoma therefore was 100%. No specific CEUS pattern could be identified to differentiate between benign and malignant nodules. CONCLUSIONS: RTE seems to be a useful tool in the work-up of thyroid nodules to exclude papillary thyroid cancer. However, follicular carcinoma remains a challenging problem. CEUS did not improve the characterization of thyroid nodules in this preliminary study.

Primary actinomycosis of the liver mimicking malignancy.

A 71-year old women presented with fever, a significant loss of body weight and abdominal pain in the upper right quadrant since approximately six months. Abdominal ultrasonography and magnetic resonance imaging (MRI) showed an irregularly shaped, inhomogeneous and hypointense lesion of the right liver lobe (6 x 8 cm in segment 7 and 8) with multiple satellite lesions. Irregular shape, hypovascular presentation during gadolinium enhancement, hypointensity in T 1-weighted images and dilation of peripheral bile ducts were suggestive for cholangiocarcinoma or metastasis. However, histological investigations revealed a rare case of primary actinomycosis of the liver which was successfully treated with antibiotics.

Suppression of the DNA damage response in acute myeloid leukemia versus myelodysplastic syndrome.

The molecular mechanisms responsible for the evolution from the preleukemic entities of low-risk myelodysplastic syndrome (MDS) to the less favorable forms of high-risk MDS, as well as those enabling transformation to acute myeloid leukemia (AML), are still incompletely understood. Abundant evidence from solid tumors demonstrates that preneoplastic lesions activate signaling pathways of a DNA damage response (DDR), which functions as an 'anticancer barrier' hindering tumorigenesis. Testing the hypothesis that subgroups of MDS and AML differ with respect to DDR, we first assessed markers of DDR (phosphorylation of ATM, Chk-1, Chk-2 and H2AX) in cell lines representing different entities of MDS (P39, MOLM-13) and AML (MV4-11, KG-1) before and after gamma-irradiation. Although gamma-irradiation induced apoptosis and G(2)/M arrest and a concomitant increase in the phosphorylation of ATM, Chk-1 and H2AX in MDS-derived cell lines, this radiation response was attenuated in the AML-derived cell lines. It is noteworthy that KG-1, but not P39 cells exhibit signs of an endogenous activation of the DDR. Similarly, we found that the frequency of P-ATM(+) cells detectable in bone marrow (BM) biopsies increased in samples from patients with AML as compared with high-risk MDS samples and significantly correlated with the percentage of BM blasts. In contrast, the frequency of gamma-H2AX(+) cells was heterogeneous in all subgroups of AML and MDS. Whereas intermediate-1 MDS samples contained as little P-Chk-1 and P-Chk-2 as healthy controls, staining for both checkpoint kinases increased in intermediate-2 and high-risk MDS, yet declined to near-to-background levels in AML samples. Thus the activation of Chk-1 and Chk-2 behaves in accord with the paradigm established for solid tumors, whereas ATM is activated during and beyond transformation. In conclusion, we demonstrate the heterogeneity of the DDR response in MDS and AML and provide evidence for its selective suppression in AML because of the uncoupling between activated ATM and inactive checkpoint kinases.

[Diagnostic spectrum of reactive lymph node changes]. / Das diagnostische Spektrum reaktiver Lymphknotenveränderungen.

Diagnostic lymph node pathology is primarily focused on identification, definition and classification of lymphoid neoplasms. Less attention is paid to reactive lymph node changes as their causes often cannot be elucidated. We outline several particular types of lymph node reactions that allow a delineation of potential causative agents. A thorough understanding of the morphology of reactive lymph node changes can also aid in the differential diagnosis between reactive and neoplastic lymph node changes.

First case of successful allogeneic stem cell transplantation in an HIV-patient who acquired severe aplastic anemia.

We report on the first successful allogeneic stem cell transplantation (SCT) in an HIV-infected patient with severe aplastic anemia (SAA) per- formed at a tertiary care institution. Highly active antiretroviral therapy (HAART) was administered until transplantation and restarted 34 days later with sustained virological response. The patient did however develop a rapid rise in HIV load during the interruption of HAART associated with an acute febrile illness. Due to the extended period between the onset of SAA until SCT, the posttransplant course was complicated by bacterial infections. Stage two skin GvHD, but no AIDS-defining opportunistic diseases were experienced. Neutrophils recovered to >0.5/nL on day +18 and the CD4 count reached 250/microL on day +71 and >500/microL on day +182. The patient is in good condition with an ECOG score of 0 twelve months after transplantation. This report demonstrates the feasibility of allogeneic stem cell transplantation in the HIV setting.

Epstein-barr virus-associated posttransplant lymphoproliferative disorder of donor origin after simultaneous pancreas-kidney transplantation limited to pancreas allograft: A case report.

A 45-year-old man was admitted with fever and elevated pancreas enzymes 6 months after simultaneous pancreas-kidney transplantation (SPKT). Function of the allografts was normal. Bacterial and fungal infections were excluded, while Epstein-Barr virus (EBV)-polymerase chain reaction (PCR) was positive. However, screening for EBV-associated lymphoma was negative. EBV infection did not respond to antiviral therapy. After an 18F-Fluorodeoxyglucose positron emission tomography positive signal and an abnormal computed tomography scan of the pancreas transplant, a biopsy revealed a diffuse large monomorphic B-cell lymphoma, which was confined to the grafted organ. Its origin was assigned to the donor by microsatellite analysis. Reduction of immunosuppression and immunotherapy with rituximab was unsuccessful. After 10 weeks, the patient developed an acute hemolytic uremic syndrome which required explantation of the allografts. Subsequent to the intervention, fever disappeared, EBV DNA became undetectable and lymphoma screening remained negative. In posttransplant lymphoproliferative disorder of donor origin after SPKT, transplantectomy may be a curative therapy.

Noninvasive assessment of liver steatosis, fibrosis and inflammation in chronic hepatitis C virus infection.

BACKGROUND: Duplex-Doppler ultrasound is a noninvasive method for the assessment of hepatic hemodynamics beyond conventional gray-scale imaging. The clinical value of the method for the grading and staging of chronic hepatitis C virus (HCV) infection and the prediction of hepatic steatosis still has to be determined. This study aimed to compare Duplex-Doppler and ultrasound with the histologic staging and the estimation of hepatic steatosis in chronic HCV infection. PATIENTS AND METHODS: One hundred and nineteen consecutive patients with chronic HCV infection underwent both liver biopsy and ultrasound with Duplex-Doppler. Maximum portal venous blood flow velocity, portal venous flow undulation, hepatic venous flow pattern and spleen size were assessed and compared with histologic findings. Histologic grading and staging was performed according to the modified HAI and hepatic steatosis was estimated. RESULTS: Doppler ultrasound was unable to discriminate between different degrees of fibrosis. Sensitivity/specificity of portal venous flow and undulations for the diagnosis of hepatic cirrhosis was 74.5%/53% and 76.5%/100%. The PPV and NPV of reduced undulations was 100% and 96.2%. Mono- or biphasic hepatic venous flow indicated advanced hepatic steatosis (sensitivity 88.2%, specificity 74.5%, PPV 36.6%, NPV 97.5%). Spleen size was significantly enlarged both in patients with cirrhosis and steatosis. CONCLUSIONS: Although Duplex-Doppler of the portal and hepatic veins is not a substitute for histologic grading and staging, portal vein undulations can predict liver cirrhosis with considerable accuracy. Moreover, triphasic patterns of hepatic venous flow virtually exclude significant fatty liver disease. Additional studies should perform intraindividual follow-up investigations to further define the role of Duplex-Doppler ultrasound in chronic HCV infection.

Bone marrow changes in chronic myelogenous leukaemia after long-term treatment with the tyrosine kinase inhibitor STI571: an immunohistochemical study on 75 patients.

AIMS: To carry out an immunohistochemical study on bone marrow (BM) biopsy specimens in 75 patients with chronic myelogenous leukaemia (CML) on long-term STI571 therapy. METHODS AND RESULTS: Sequential BM specimens taken at intervals of 21 +/- 6 months were investigated by enzyme- and immunohistochemistry including proliferating cell nuclear antigen and apoptosis. Evaluation was performed either by semiquantitative scoring or by morphometry (CD61+ megakaryopoiesis). In 41 patients with chronic phase CML, treatment resulted in a significant decrease in cellularity and neutrophil granulopoiesis contrasting with an accumulation of erythroid precursor cells. Morphometry showed a reduction of abnormal micromegakaryocytes consistent with normalization. Regression of myelofibrosis was identified in eight of 15 patients, whereas progression occurred in 17 patients; mostly in those with acceleration and blastic crisis. The increased post-treatment incidence of reactive lymphoid nodules was remarkable. Myeloblasts, CD34+ progenitors and immature myelomonocytic cells initially decreased, but recurred in 14 patients who later developed a relapse. STI571 exerted an inhibitory effect on cell proliferation associated with enhanced apoptosis in responding patients. CONCLUSION: Long-term treatment with STI571 exerts pronounced changes on BM histopathology that not only involve haematopoiesis and stromal constituents, but also proliferation and apoptosis.

[Five-year results following autogenous osteochondral transplantation to the femoral head]. / 5-Jahres-Ergebnisse nach autologer Knorpel-Knochen-Transplantation bei Hüftkopfnekrose.

The rationale for autogenous osteochondral grafting into necrotic areas of the femoral head is to provide hyaline cartilage for areas of main articular contact pressure. The aim of this study was to present our results of autogenous osteochondral grafting to the femoral head in the treatment of avascular necrosis. The mean follow-up of the five patients was 57 months following autogenous osteochondral grafting to the femoral head using DBCS (diamond bone-cutting system). The number of transplanted cylinders varied between one and three, and the diameter of the cylindrical transplants between 9 and 13 mm. Results were unsatisfactory in four of five hips and these underwent total hip replacement a mean of 49 months following DBCS of the hip. In our hands, osteochondral grafting to the femoral head using DBCS had proven technically possible in restoring the articular surface of the femoral head; however, this operation was associated with unsatisfactory results in four of five cases.

Effects of the tyrosine kinase inhibitor imatinib mesylate (STI571) on bone marrow features in patients with chronic myelogenous leukemia.

Preliminary data are available about bone marrow (BM) changes in patients with chronic myeloid leukemia (CML) who received the molecularly targeted and highly effective tyrosine kinase inhibitor Imatinib mesylate (STI571). This review is focused on a systematic assessment of BM features detectable at different stages of CML (stable, accelerated, blastic) following long-term (more than 10 months) treatment. By applying enzyme- and immunohistochemistry including monoclonal antibodies visualizing proliferating cell nuclear antigen (PCNA) and apoptosis (anti-apostatin), a more elaborate insight into alterations affecting hematopoiesis and the stroma compartment was gained. In patients with stable-phase CML therapy resulted in a significant reduction in cellularity, neutrophil granulopoiesis and number of megakaryocytes, accompanied by a retrieval of erythroid precursors. In patients with Imatinib as the only treatment morphometric analysis of CD61+ megakaryopoiesis was in keeping with a significant decrease in maturation defects implying a lesser amount of atypical micromegakaryocytes almost consistent with normalization. Moreover, a reduction of the initially enhanced (CD34+) microvessel density was detectable associated with a decrease in luminal distension. Regression of marked to moderate myelofibrosis was recognizable in about 70% of patients especially in the accelerated and blastic phases. The amount of myeloblasts, CD34+ progenitor cells and lysozyme-expressing immature myelomonocytic cells declined with treatment, but recurred in about 19% of patients that developed a leukemic relapse after 21+/-6 months of therapy. Data on proliferative activity and apoptosis in general supported in vitro findings concerning the inhibitory effect of this agent on growth associated with a tendency for stimulated apoptosis, at least in responding patients.

[Regression of the Philadelphia chromosome (bcr/abl)-positive myelo- and megakaryopoiesis after Imatinib (STI571) therapy in chronic myelogenous leukemia (CML)]. / Regression der Philadelphia-Chromosom (bcr/abl)-positiven Myelo- und Megakaryopoiese unter Imatinib(STI571)-Therapie bei chronischer myeloischer Leukämie (CML).

In chronic myeloid leukemia following therapy with Imatinib (STI571) hematologic and cytogenetic response is associated with conspicuous changes of bone marrow morphology. However, it is not known to which extent these alterations are accompanied by a loss of the bcr/abl translocation. To study regression of the leukemic cell population we recruited 14 patients lacking pretreatment. Therapy resulted in a reduction of CD61(+) megakaryopoiesis. Dwarf megakaryocytes characteristic for this disorder were replaced by large, normally appearing cells of this lineage. Morphometric analysis confirmed the significant decrease in the number of micromegakaryocytes and yielded planimetric parameters in keeping with normalization. Moreover, a fluorescence in-situ hybridization study in five patients of this cohort revealed that before therapy 70% of all myeloid cells exhibited the bcr/abl gene. Regarding megakaryopoiesis about 65% of the micromegakaryocytes displayed positive signals. Following treatment these bcr/abl(+) cell populations decreased significantly while the emerging large megakaryocytes lacked a proper labeling. Because cytogenetic response and reduction of atypical micromegakaryocytes are linked, this feature may be useful to monitor therapeutic efficacy.

[Therapy-related changes of angiogenesis in Philadelphia chromosome positive chronic myelogenous leukemia]. / Therapie-bedingte Veränderungen der Angiogenese bei Philadelphia-Chromosom-positiver chronischer myeloischer Leukämie.

To elucidate the effect of first-line treatment with interferon (IFN), hydroxyurea (HU) and the tyrosine kinase inhibitor imatinib (STI571) on angiogenesis, we studied bone marrow (BM) biopsies in 104 patients with chronic myelogenous leukemia (CML) and 138 patients before and after allogeneic BM transplantation (BMT). After immunostaining (CD34) and morphometric analysis in comparison with a control group, CML specimens showed an increased vascularity and conspicuous morphological abnormalities of microvessels. A close relationship between microvessels and fiber density was detectable in initial biopsies and also in repeatedly performed examinations following therapy. Monotherapy by imatinib and HU generated a significant reduction of microvessels and reticulin fibers in contrast to changes after IFN administration or combination regimens of IFN and HU. A persistence of numerical and structural anomalies of vasculature was observable even several months after BMT. These anomalies shed some light on disturbances of the stroma compartment after myeloablative therapy. The relationship between BM vascularity and fibers is probably dependent on concomitant changes of megakaryopoiesis as the source of various mediators involved in the development of myelofibrosis and neo-angiogenesis acting within a complex functional network.

Pheochromocytoma in childhood: implication for further diagnostic procedures.

UNLABELLED: We report on our experience with two patients with pheochromocytoma. One patient underwent surgery of pheochromocytoma at the age of 30 y; 18 y later, medullary thyroid carcinoma (MTC) was detected in his son. Subsequently, multiple endocrine neoplasia (MEN) type 2A was diagnosed by genetic examination in both father and son. Further diagnostic procedures also revealed an MTC in the father. The other patient suffered from bifocal pheochromocytoma of the left suprarenal gland. Diagnostic work-up revealed papillary thyroid carcinoma, which was also detected in the mother 8 mo later. Whereas a point mutation in SDHB gene was found in the son, no genetic abnormality was detected in the mother. CONCLUSION: Every pheochromocytoma in childhood warrants further diagnostic work-up, including genetic examination. In addition, clinical data of patients suffering from pheochromocytoma and papillary thyroid carcinoma should be collected by an international registry, and a joint effort should be undertaken in order to define possible underlying mutated genes in these patients.

Paraneoplastic syndromes: detection of malignant tumors using [(18)F]FDG-PET.

AIM: Paraneoplastic syndromes (PS) comprise a variety of clinical symptoms and diseases associated with underlying malignancy. Differentiation towards benign autoimmune diseases is necessary due to different therapeutic options. This diagnostic challenge includes cost- and time-consuming methods and is not successful in many cases. The aim of this study was the evaluation of [(18)F]fluorodeoxyglucose positron emission tomography ([(18)F]FDG-PET) for detecting or ruling out malignancy in these patients. METHODS: In this retrospective work-up a total of 30 patients with suspected PS (m:f = 17:13, mean age 55, range 22-76 years) were examined with [(18)F]FDG-PET between 1996 and 2001. Diagnoses were erythrodermia, cerebellar degeneration, dermatomyositis, polyneuropathia and others. PET scans were compared to histopathological (n=14), radiological and follow up data (mean follow up 3.6 years, range 1-6 years). RESULTS: In 7 out of 30 patients (23%) an underlying malignancy was detected. Six out of 7 malignant neoplasms showed a distinctly increased glucose consumption. One benign neoplasm caused increased tracer uptake, another PET positive patient refused biopsy and showed no growth of a malignant tumour during clinical follow up of 28 months. The remaining 21 patients without suspicious glucose consumption did not demonstrate a malignancy in other diagnostic modalities or during subsequent clinical follow-up. CONCLUSION: [(18)F]FDG-PET seems to be a useful tool in the diagnostic work-up of patients with suspected paraneoplastic syndrome.

Frequency of the Amsterdam criteria in a regional German cohort of patients with colorectal cancer.

Estimates of the colon cancer burden associated with hereditary nonpolyposis colorectal cancer (HNPCC) vary from less than 1 % to more than 5 %. Amsterdam criteria fulfilled within a kindred (classic Amsterdam and Amsterdam II criteria) are widely used to identify patients prone to HNPCC. The present study was initiated to assess the frequency of the Amsterdam criteria within a regional German cohort of 207 patients with a history of colorectal cancer (CRC). Data on individual and family cancer histories were available in 154 patients (73 women, 81 men; mean age at diagnosis 62.4 +/- 13.3 years). A total of 843 first degree relatives have been identified within the kindreds of whom 121 had verified cancers. In 28 of 154 families (18 %), at least one first degree relative of the index patient had CRC. With respect to a typical family history, five kindreds (3.2 %) were likely to suffer from HNPCC on a clinical basis (4 kindreds met the classic Amsterdam criteria and one kindred the Amsterdam II criteria). Testing for microsatellite instability could additionally be performed in 4 of 5 patients who met the Amsterdam criteria and revealed DNA instability in 3 cases. Moreover, a missense mutation of MSH2 (Gly965Asp) was detected in one patient with microsatellite instability. Based on the classic Amsterdam and Amsterdam II criteria approximately 3 % of a regional German cohort of patients with CRC are likely to suffer from HNPCC. However, the final diagnosis of HNPCC can only be established by detection of pathogenic germline mutations within the DNA mismatch repair genes.

Bethesda guidelines: relation to microsatellite instability and MLH1 promoter methylation in patients with colorectal cancer.

BACKGROUND: Microsatellite instability is a hallmark of mismatch repair deficiency in hereditary nonpolyposis colorectal cancer and results from mutations in the mismatch repair genes MLH1 or MSH2 or from gene inactivation associated with DNA methylation. The Bethesda guidelines were established to identify patients with colorectal cancer who should be tested for microsatellite instability. OBJECTIVE: To assess the Bethesda guidelines for detection of microsatellite instability and to determine the role of MLH1 promoter methylation in colorectal cancer. DESIGN: Prospective cohort study. SETTING: Tertiary care referral center in Frankfurt, Germany. PATIENTS: 125 consecutive patients with colorectal cancer. MEASUREMENTS: Patients were assessed according to the Bethesda guidelines, and tumor specimens were analyzed for microsatellite instability. Patients with microsatellite instability were tested for MLH1 promoter methylation and MLH1 and MSH2 germline mutations. RESULTS: Microsatellite instability was detected in 17 of 58 patients who fulfilled and 5 of 67 patients who did not fulfill criteria of the Bethesda guidelines. In 11 of 17 patients with microsatellite instability who fulfilled Bethesda guidelines, an MLH1 (n = 3), MSH2 (n = 7), or combined MLH1 and MSH2 (n = 1) mutation was found. Among the patients with microsatellite instability who did not fulfill Bethesda guidelines, no mutations were observed; MLH1 promoter methylation was observed in 6 of 11 patients with an MLH1 or MSH2 mutation and 5 of 11 patients without an MLH1 or MSH2 mutation. CONCLUSIONS: The Bethesda guidelines are useful for selecting patients for microsatellite instability testing. MLH1 and MSH2 testing should be recommended in all patients with colorectal cancer and microsatellite instability who fulfill at least one Bethesda criterion. MLH1 promoter methylation may accompany rather than initiate carcinogenesis in patients with colorectal cancer who have mismatch repair gene defects.