Real-world data of AML in Japan: results of JALSG clinical observational study-11 (JALSG-CS-11).

This report covers acute myeloid leukemia (AML) results from a multicenter, prospective observational study of AML, myelodysplastic syndromes, and chronic myelomonocytic leukemia in Japan. From August 2011 to January 2016, 3728 AML patients were registered. Among them, 42% were younger than 65, and the male-to-female ratio was 1.57:1. With a median follow-up time of 1807 days (95% confidence interval [CI]: 1732-1844 days), the estimated 5-year overall survival (OS) rate in AML patients (n = 3707) was 31.1% (95% CI: 29.5-32.8%). Trial-enrolled patients had a 1.7-fold higher OS rate than non-enrolled patients (5-year OS, 58.9% [95% CI: 54.5-63.1%] vs 35.5% [33.3-37.8%], p < 0.0001). Women had a higher OS rate than men (5-year OS, 34% [95% CI; 31.4-36.7%] vs 27.7% [25.7-29.7%], p < 0.0001). The OS rate was lower in patients aged 40 and older than those under 40, and even lower in those over 65 (5-year OS for ages < 40, 40-64, 65-74, ≥ 75: 74.5% [95% CI; 69.3-79.0%] vs 47.5% [44.4-50.6%] vs 19.3% [16.8-22.0%] vs 7.3% [5.5-9.4%], respectively). This is the first paper to present large-scale data on survival and clinical characteristics in Japanese AML patients.

Real-world data of MDS and CMML in Japan: results of JALSG clinical observational study-11 (JALSG-CS-11).

We conducted a multicenter, prospective observational study of acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and chronic myelomonocytic leukemia (CMML) in Japan. From August 2011 to January 2016, we enrolled 6568 patients. Herein, we report the results for MDS (n = 2747) and CMML (n = 182). The percentage of patients aged 65 years or older was 79.5% for MDS and 79.7% for CMML. The estimated overall survival (OS) rate and cumulative incidence of AML evolution at 5 years were 32.3% (95% confidence interval: 30.2-34.5%) and 25.7% (23.9-27.6%) for MDS, and 15.0% (8.9-22.7%) and 39.4% (31.1-47.6%) for CMML. Both diseases were more common in men. The most common treatment for MDS was azacitidine, which was used in 45.4% of higher-risk and 12.7% of lower-risk MDS patients. The 5-year OS rate after treatment with azacitidine was 12.1% (9.5-15.1%) for of higher-risk MDS patients and 33.9% (25.6-42.4%) for lower-risk patients. The second most common treatment was erythropoiesis-stimulating agents, given to just 20% of lower-risk patients. This is the first paper presenting large-scale, Japanese data on survival and clinical characteristics in patients with MDS and CMML.

Hepatocyte proliferation activity in untreated rats, measured by immunohistochemical detection of Ki-67: The effect of age on the repeated-dose liver micronucleus assay.

The repeated-dose liver micronucleus (RDLMN) assay is a widely accepted method for detecting genotoxic substances. We investigated the effect of animal age on this assay. Proliferation activity in the liver tissue of untreated rats at age = 3.5, 6, 8, 10, or 12 weeks was measured via immunohistochemical expression of Ki-67 protein. The percentage of Ki-67-positive hepatocytes decreased markedly with age, reaching very low levels after 10 weeks, indicating decline with age of proliferative capacities in the liver. We calculated the area under the curve (AUC) of the approximate curve generated from the percentage of Ki-67-positive cells, to estimate the hepatocyte proliferation activity over the dosing period in the two regimens of the 4-week RDLMN assay: dosing initiated at age = 6 or 8 weeks. Hepatocyte proliferation activity of the former regimen was approximately double that of the latter. We also calculated the AUC for the juvenile-rat method, in which rats are treated for two days at age = 3.5 weeks. The AUC calculated for that method was approximately half of that for the 4-week repeated-dosing regimen initiated at 6 weeks of age. These findings suggest that the 4-week RDLMN assay with dosing initiated at age = 6 weeks could be approximately twice as sensitive as the other two methods.

Evaluation of the reproducibility and positive controls of cellular immortality test for the detection of immortalized cellular impurities in human cell-processed therapeutic products.

Introduction: Contamination of human cell-processed therapeutic products (hCTPs) with tumorigenic/immortalized cellular impurities is a major concern in the manufacturing and quality control of hCTPs. The cellular immortality test based on cell growth analysis is a method for detecting tumorigenic/immortalized cellular impurities in hCTPs. However, the performance of the cellular immortality test has not yet been well characterized. In this study, we examined the reproducibility of the cellular immortality test in detecting HeLa cells as a model of tumorigenic cellular impurities, as well as the applicability of other models of cellular impurities with different tumorigenicity to the cellular immortality test. Methods: Using HeLa cells as a model for cellular impurities, we measured the growth rate of human mesenchymal stem cells (hMSCs) supplemented with HeLa cells at concentrations ranging from 0.01 to 0.0001% at each passage in three laboratories and evaluated the reproducibility of the detection of immortalized cellular impurities. In addition, HEK293 cells (another immortalized cell line) and MRC-5 cells (a non-immortalized cell line) were employed as cellular impurity models that exhibit different growth characteristics from HeLa cells, and the ability of the cellular immortality test to detect these different impurities when mixed with hMSCs was examined. Results: In the multisite study, the growth rate of hMSCs supplemented with 1 and 10 HeLa cells (0.0001% and 0.001%) significantly increased and reached a plateau in all three laboratories, whereas those of hMSCs alone eventually decreased. Moreover, when hMSCs were supplemented with 10 and 100 HEK293 and MRC-5 cells (0.001% and 0.01%), the growth rate significantly increased. The growth rate of hMSCs supplemented with HEK293 cells increased with passage and remained high, whereas that of hMSCs supplemented with MRC-5 cells eventually decreased, as in the case of hMSCs alone. Conclusions: These results indicate that the cellular immortality test is reproducible and can detect immortalized (i.e., potentially tumorigenic) cells such as HEK293 cells with a lower growth rate than HeLa cells by discriminating against normal cells, which could contribute to ensuring the safety and quality of hCTPs.

Lack of hepatocarcinogenicity of 2,2'-[1,2-ethanediylbis(oxymethylene)]bis-oxirane, 3-hydroxy-2-naphthoic acid, and acetoacetanilide in a medium-term rat liver bioassay.

The carcinogenicity of 2,2'-[1,2-ethanediylbis(oxymethylene)]bis-oxirane (ethylene glycol diglycidyl ether; EGDE), 3-hydroxy-2-naphthoic acid (HNA), and acetoacetanilide (AAA) was investigated using a medium-term rat liver bioassay for an occupational safety assessment. F344 male rats were administered a single intraperitoneal injection of diethylnitrosamine (200 mg/kg body weight (bw)/day) and then starting 2 weeks later, they received EGDE at 6, 20, and 60 mg/kg bw/day, HNA at 20, 60, and 200 mg/kg bw/day, or AAA at 60, 200, and 600 mg/kg bw/day by oral gavage for 6 weeks. The animals in the positive control group received phenobarbital sodium solution (PB, 25 mg/kg bw/day) by oral gavage and those in the negative control group received a vehicle (water/corn oil) during the administration period of test substances in this model. All animals were subjected to two-thirds partial hepatectomy at week 3 and euthanized at week 8. Neither the number nor the area of hepatocellular foci positive for glutathione S-transferase placental form (GST-P) increased in any of the EGDE, HNA, or AAA treated groups. However, the number and area of GST-P-positive foci significantly increased in the positive control group treated with PB. The results indicate that EGDE, HNA, and AAA lack hepatocarcinogenicity in rats.

The effect of aging on the repeated-dose liver micronucleus assay using diethylnitrosamine.

BACKGROUND: The repeated-dose liver micronucleus (RDLMN) assay has been well-developed and applied because of its simplicity and the ease of integration into general toxicity studies which is the preferred method from the 3R's point of view. In this assay, we observed micronucleated hepatocytes which accumulated during a rather long-term dosing period. When considering integration into general toxicity studies, the effects of age of the animals used in the micronucleus assay becomes a major issue. The effect of age on the micronucleus induction rate has been reported in bone marrow micronucleus assays, and it is considered that the decrease in cell proliferation rate due to aging is the cause of the decrease in sensitivity. A decrease in sensitivity due to aging was also reported in a liver micronucleus assay using clofibrate and the cause is considered to be a decrease in hepatocyte proliferation activity due to aging. However, no actual decrease in hepatocyte proliferation rate due to aging has been reported. In addition, there are no reports, so far, on whether similar effects of aging appear when other substances were administered. To investigate the effects of aging in the RDLMN assay, this study focused on the effects of 14-day repeated administration of DEN, a well-known genotoxic hepatocarcinogen with the hepatocyte toxicity which should cause an elevation of cell proliferation rate as a reflective regeneration. RESULTS: The liver micronuclei induced by DEN were equivalent between the two age groups (i.e., six and eight weeks of age at the start of dosing). In the histopathological examination for the liver, single cell necrosis, karyomegaly, and increased mitosis were observed in the hepatocytes, and the frequency and severity were increased dose-dependently. Ki-67 immunohistochemical analysis which can detect all cells in the cell cycle other than those in the G0 phase revealed dose-dependent increase of cell proliferation activity, and the difference between ages was not observed. CONCLUSION: The effect of aging on the RDLMN assay could not be recognized when DEN was administered for 14 days in rats. Meanwhile, it was supported by the histopathological examination and Ki-67 immunohistochemical analysis that such an effect of aging was masked by the compensatory hepatocyte proliferation which was induced by the hepatocyte toxicity of DEN.

[Successful treatment of high-dose methotrexate-induced oliguric acute renal failure by using a combination of hemodialysis filtration and direct hemoperfusion].

A 64-year-old man with central nervous system metastases from systemic non-Hodgkin lymphoma was treated with high- dose intravenous methotrexate(MTX 3.5 g/m2). The patient subsequently developed oliguric acute renal failure 12 hours after MTX initiation, and his serum MTX level was 163 mM at 26 hours. Hemodialysis filtration(HDF)combined with direct hemoperfusion(DHP)was initiated at 45hours. Seven sessions of combined HDF and DHP and 2 courses of HDF alone were performed, and the mean MTX extraction rates were 68.2% and 74.3%, respectively. The patient experienced severe respiratory failure, febrile neutropenia, myelosuppression, and oral mucositis. However, his urine output began to improve on day 7 after MTX initiation, and his renal function gradually recovered. His serum MTX level declined to 0.04 mM on day 23 after MTX initiation. In the present case, we immediately initiated HDF and DHP and successfully treated the patient for MTX-induced renal failure.

Highly frequent and enhanced injection site reaction induced by peripheral venous injection of fosaprepitant in anthracycline-treated patients.

BACKGROUND: Fosaprepitant-associated injection site reaction (ISR) has been reported in patients treated with cisplatin, an irritant drug. We conducted this retrospective study to clarify the incidence and symptoms of fosaprepitant-associated ISR in patients treated with anthracycline. PATIENTS AND METHODS: Fifty six patients receiving 159 injections administering doxorubicin/cyclophosphamide (AC), fluorouracil/epirubicin/cyclophosphamide (FEC), or rituximab/cyclophosphamide/doxorubicin/vincristine/prednisolone (R-)CHOP regimen through a peripheral vein at ambulatory treatment centers reviewed for this study from patients' medical records. Incidence of ISR was compared between 24 patients with fosaprepitant injection (fosaprepitant group) and 32 patients without fosaprepitant (control group). Frequency and symptoms of ISR per injection were also compared between 61 injections with fosaprepitant and 98 injections without fosaprepitant. RESULTS: Both the ISR incidence rate per patient and per injection were significantly higher in the fosaprepitant group than in the control group (67% vs. 16%; P=0.0002, 34% vs. 8.2%; P<0.0001, respectively). By multivariate analysis, fosaprepitant injection was found to be a significant independent variable correlated with ISR risk. Symptoms observed in 61 injections of fosaprepitant were pain (n=14, 23%), erythema (n=10, 16%), swelling (n=6, 10%), and delayed drip infusion (n=6, 10%). After the observation period, no ISR occurred when the administration route was changed to central venous injection or oral aprepitant was administered despite the continuation of chemotherapy. CONCLUSION: ISR occurred more frequently and severely when fosaprepitant was injected through the peripheral vein in patients treated with anthracyclines compared to those without fosaprepitant.

Intravascular lymphomatosis mimicking primary central nervous system lymphoma: a case report and literature review.

We herein report a 75-year-old female patient with intravascular lymphomatosis (IVL) who presented with fever of unknown origin. Examination, including contrast-enhanced CT and (67)Ga scintigraphy, failed to show any lesions. Her blood levels of lactate dehydrogenase and soluble interleukin-2 receptors were high, suggesting a lymphomatous tumor. A bone marrow puncture was negative, and a random skin biopsy revealed a monoclonal proliferation of naked, large lymphocytes in the vascular space of the subcutaneous tissue, confirming the diagnosis of IVL. MRI, performed 7 weeks after admission, showed a brain mass mimicking primary central nervous system lymphoma. The mass was considered to be a collection of malignant lymphocyte cells invading from the vessels. Without the random skin biopsy, this case may have been misdiagnosed as primary central nervous system lymphoma.

[A case of acute myeloid leukemia in an obese patient--determining the therapeutic dose of anticancer drugs].

Currently, there is no consensus to determine whether the therapeutic doses of anticancer drugs should be based on the actual or the ideal body weight of obese cancer patients. We performed induction and consolidation chemotherapy at doses calculated by using the actual body weight of an obese patient with acute myeloid leukemia (AML). A 47-year-old Japanese man presented with pancytopenia at our hospital, and he was diagnosed with AML (FAB classification M0). At the initial diagnosis, the patient was 170 cm tall and weighed 132 kg; therefore, his body surface area was 2.37 m(2). His performance status and organ functions were quite good. The calculations for determining doses of anticancer drugs required were based on his actual body weight. He received induction chemotherapy and achieved complete remission. Subsequently, he was treated with 4 courses of consolidation chemotherapy. Febrile neutropenia was a complication during each course, and it was relieved via myeloid recovery. Chemotherapy was administered every 4-5 weeks, except for the second course where platelet recovery was prolonged, and the prescribed treatment was completed. The guidelines of the American Society of Clinical Oncology (ASCO) recommend that physicians routinely use an obese patient's actual body weight to calculate the appropriate doses of almost all chemotherapy drugs. Therefore, the ease and compromised usage of under-dosing because of heaviness owing to obesity should be avoided.

Enhanced liver tumor promotion but not liver initiation activity in rats subjected to combined administration of omeprazole and ß-naphthoflavone.

Omeprazole (OPZ) and ß-naphthoflavone (BNF) are cytochrome P450 (CYP)1A inducers and have liver tumor promoting effects. In this study, we investigated the co-promoting and co-initiating effects of OPZ and BNF in rats. In Experiment 1, male rats were subjected to partial hepatectomy (PH), and given oral doses of 138 or 276 mg/kg OPZ, 0.125% or 0.25% BNF or 138 mg/kg OPZ+0.125% BNF (n = 9~12) for 6 weeks after N-diethylnitrosamine (DEN) initiation. In Experiment 2, male rats were treated with oral doses of 138 or 276 mg/kg OPZ, 0.03% or 0.06% BNF or 138 mg/kg OPZ+0.03% BNF (n = 11~12) for 9 days starting 1 week before initiating treatment. As an initiating treatment, 2-Amino-3,4-dimethylimidazo[4,5-f]quinolone (MeIQx) was orally administered 12 hr after PH. The rats were fed a basal diet for 15 days, followed by a diet containing 0.015% 2-acetylaminofluorene for the next 10 days with a single oral dose of carbon tetrachloride. In Experiment 1, the number and area of glutathione S-transferase placental form-positive foci in the OPZ+BNF group were significantly higher than the average values of the High OPZ or the High BNF group. The expression of cyclooxygenase-2 (Cox-2) and COX-2 protein in the liver significantly increased in the OPZ+BNF group. In Experiment 2, liver initiation activity was not enhanced by the co-administration of OPZ+BNF. The results of our studies suggest that the co-administration of OPZ and BNF results in synergistic effects in the liver tumor promotion probably owing to increased COX-2 expression, but no modifying effect in the liver initiation activity of MeIQx in rats.

Phase 1 trial of gemtuzumab ozogamicin in combination with enocitabine and daunorubicin for elderly patients with relapsed or refractory acute myeloid leukemia: Japan Adult Leukemia Study Group (JALSG)-GML208 study.

We conducted a phase 1 study of a combination of gemtuzumab ozogamicin (GO) plus conventional chemotherapy in elderly patients (≥ 65 years old) with relapsed or refractory CD33-positive acute myeloid leukemia (AML). Patients received a standard dose of enocitabine (200 mg/m² × 8 days) and daunorubicin (30 mg/m² × days 1-3) plus an escalating dose of GO (1.5-5 mg/m² on day 4). The dose escalation of GO was done according to a standard 3 + 3 design following a modified Fibonacci sequence. No dose-limiting toxicities were observed in three patients (median age, 71) at level 1 (1.5 mg/m²) or in three patients (median age, 73) at level 2 (3 mg/m²). Neither veno-occlusive diseases nor sinusoidal obstructive syndromes were noted at either level. However, as GO was withdrawn from the US market in June 2010, based on a randomized study in newly diagnosed AML, we decided not to proceed to the level 3 (5 mg/m²) in order to avoid possibly more severe adverse effects, and also because all six patients experienced grade 4 myelosuppression, with complete remission in three. This study showed that 3 mg/m² of GO in combination with enocitabine and daunorubicin may be a recommendable dose for a phase 2 study in Japanese elderly patients with CD33-positive AML. The study was registered at the University Hospital Medical Information Network (UMIN) Clinical Trials Registry ( http://www.umin.ac.jp/ctr/ ) as UMIN000002603.

Randomized comparison of fixed-schedule versus response-oriented individualized induction therapy and use of ubenimex during and after consolidation therapy for elderly patients with acute myeloid leukemia: the JALSG GML200 Study.

We conducted a multicenter prospective randomized study to compare a fixed-scheduled induction therapy with a response-oriented individualized induction therapy for elderly patients with acute myeloid leukemia (AML). Newly diagnosed AML patients, aged between 65 and 80, were randomly assigned to receive fixed or individualized induction. Both groups received daunorubicin (DNR) 40 mg/m(2) for 3 days and behenoyl cytarabine (BHAC) 200 mg/m(2) for 8 days. In the individualized group, bone marrow biopsy was done on days 8 and 10, and according to the cellularity and blast ratio, the patients received additional DNR and BHAC for two to four more days. All patients achieving complete remission (CR) were randomized a second time to determine whether they would receive ubenimex. CR was obtained in 60.1 % of the fixed group and 63.6 % of the individualized group. Predicted 4-year relapse-free survival (RFS) was 9 % for the fixed group and 18 % for the individualized group. There were no statistically significant differences in CR and RFS between the fixed and individualized groups. In the ubenimex group, prolonged RFS was observed. Notably, gender was a prognostic factor in this study, as 102 female patients had a significantly higher CR rate (72.5 vs. 54.3 %, p = 0.0048) and better OS (24 vs. 14 % at 4 years, p = 0.018), compared with 140 male patients.

Serum alkaline phosphatase isoenzymes in SD rats detected by polyacrylamide-gel disk electrophoresis.

Serum alkaline phosphatase (ALP) activity is frequently measured in toxicity studies. In the present study, we assessed the usefulness of a commercially available polyacrylamide-gel disk electrophoresis kit used in humans (AlkPhor System, Jokoh Co. Ltd., Tokyo, Japan) for identifying serum ALP isoenzymes in rats of the Sprague-Dawley strain (SD rats), which are commonly used in toxicity studies. We also examined age-related changes in serum ALP isoenzymes in SD rats. In order to identify the origin of each ALP isoenzyme, tissue ALP extracts from the liver, bone and small intestine (SI) and serum samples were treated with neuraminidase, antiintestinal ALP antibody, ALP inhibitor levamisole, and/or wheat germ agglutinin. It became clear that pretreatment of serum with neuraminidase is necessary for rat serum ALP isoenzyme analysis. The kit revealed that the main serum ALP isoenzymes in fasted 8-week-old intact rats were bone- and SI-derived and they tended to decrease with age. Serum liver-derived isoenzyme was slightly detected in both sexes of all ages examined, but it greatly increased in cholestasis model rats with bile-duct ligation, and rats of this model also had large molecular ALP detected in the stacking gel, suggesting hepatic damage. High-molecular intestinal ALP isoenzyme was slightly observed at the most cathodal side of the resolving gel. These results suggest that the present method is a useful tool for detecting serum ALP isoenzymes in SD rats and that concomitant levamisole inhibition with another gel is applicable for the evaluation of organ toxicity.

Serum alkaline phosphatase isoenzymes in laboratory beagle dogs detected by polyacrylamide-gel disk electrophoresis.

Serum alkaline phosphatase (ALP) activity is frequently measured in toxicity studies. Itoh et al. (2002) reported that a commercially available polyacrylamide-gel (PAG) disk electrophoresis kit used in humans (AlkPhor System, Jokoh Co., Ltd., Tokyo, Japan) for identifying serum ALP isoenzymes was useful for veterinary clinicopathological diagnosis in mongrel dogs. In the present study, based on the report of Itoh et al. (2002), we tried to expand the application range of this kit to laboratory beagle dogs which are commonly used in toxicity studies. In order to identify the origin of each ALP isoenzyme, tissue ALP extracts from the liver, bone and small intestine and serum samples were treated with neuraminidase, anti-small intestinal ALP antibody, ALP inhibitor levamisole and/or wheat germ agglutinin (WGA). The main serum ALP isoenzymes in 5-month-old intact beagle dogs were bone-derived (bone and atypical ALP: corresponding to human variant bone ALP) and they tended to decrease with age. However, liver-derived ALP isoenzyme greatly increased in the serum of cholestasis model dogs. The cholestasis model dogs also had a large molecular ALP detected in the resolving gel. This ALP could be originated from intestinal ALP or corticosteroid-induced ALP (CALP), because the activity remained even after levamisole inhibition. CALP was observed in intact laboratory beagle dogs with individual differences. These results suggest that the present method is a useful tool for detecting serum ALP isoenzymes in laboratory beagle dogs and concomitant levamisole inhibition with another gel is applicable for the evaluation of organ toxicity.

Alkaline phosphatase isoenzymes in mouse plasma detected by polyacrylamide-gel disk electrophoresis.

Plasma alkaline phosphatase (ALP) activity is frequently measured in toxicity studies. In the present study, we assessed the usefulness of a commercially available polyacrylamide-gel (PAG) disk electrophoresis kit used in humans (AlkPhor System, Jokoh Co., Ltd., Tokyo, Japan) for identifying plasma ALP isoenzymes in mice of the Crlj:CD1 strain (ICR mice), which are commonly used in toxicity studies. We also examined age-related changes in plasma ALP isoenzymes in ICR mice. Electrophoresis was performed according to the manufacturer's instructions. In order to identify the origin of each ALP isoenzyme, in addition to plasma samples, tissue ALP extracts from the liver, bone and small intestine were treated with neuraminidase, anti-small intestinal ALP antibody, ALP inhibitor levamisole and/or wheat germ agglutinin (WGA). The kit revealed that main plasma ALP isoenzyme in intact ICR mice was bone-derived one, and it tended to decrease with age. On the other hand, liver-derived ALP isoenzyme greatly increased in plasma of cholestasis model mice induced by bile duct ligation. This model mouse had also a large molecular ALP detected in the stacking gel. This ALP was thought to be of intestinal origin because its activity remained even after levamisole inhibition. In addition, a minimum sample volume for sufficient resolution of plasma ALP isoenzymes was only 14µl. The results of this study suggest that the present method is a useful tool for detecting plasma ALP isoenzymes in mice and that pre-treatment of plasma with neuraminidase and concomitant levamisole inhibition with another gel is applicable for the evaluation of organ toxicity.

[Characteristics of elderly patients with acute myelogenous leukemia].

The average life span of our country is the longest in the world, and rapid aging is taking place, besides. Therefore the elderly patients with acute myelogenous leukemia (EAML) is increasing. The biological characteristic of EAML is deteriorating internal organs function, and high ratios having the complication of the patient. Leukemic cells in the elderly has the biologic characteristic that non-usual case, for example hypoplastic leukemia, is many, and a case having abnormal chromosomal aberration is also. A social characteristic of EAML is that they are treated at a general hospital such as the municipal hospital not a university hospital, and in many cases the only family is the elderly spouse. Enough understanding of the nation is necessary to overcome such a disadvantageous point and to improve treatment results of EAML.

The Asn505 mutation of the c-MPL gene, which causes familial essential thrombocythemia, induces autonomous homodimerization of the c-Mpl protein due to strong amino acid polarity.

We previously reported that a dominant-positive activating mutation (Asn505) in the transmembrane domain (TMD) of c-MPL, which encodes the thrombopoietin receptor, caused familial essential thrombocythemia. Here, we show that the Asn505 mutation induces both autonomous dimerization of c-Mpl and signal activation in the absence of its ligand. Signal activation was preserved in a truncated mutant of Asn505 that lacked the extracellular domain of c-MPL. We also found that the substitution of the amino acid (AA) residue at position 505 with others of strong polarity (Glu, Asp, or Gln) also resulted in activated dimerization without ligand stimulation. Overall, these data show that the Asn505 mutation transduced the signal through the autonomous dimerization of the c-MPL protein due to strong AA polarity. This finding provides a new insight into the mechanism of disease causation by mutations in the TMD of cytokine/hematopoietic receptors.