Phase III study comparing oxaliplatin plus S-1 with cisplatin plus S-1 in chemotherapy-naïve patients with advanced gastric cancer.

BACKGROUND: We evaluated the efficacy and safety of S-1 plus oxaliplatin (SOX) as an alternative to cisplatin plus S-1 (CS) in first-line chemotherapy for advanced gastric cancer (AGC). PATIENTS AND METHODS: In this randomized, open-label, multicenter phase III study, patients were randomly assigned to receive SOX (80-120 mg/day S-1 for 2 weeks with 100 mg/m(2) oxaliplatin on day 1, every 3 weeks) or CS (S-1 for 3 weeks with 60 mg/m(2) cisplatin on day 8, every 5 weeks). The primary end points were noninferiority in progression-free survival (PFS) and relative efficacy in overall survival (OS) for SOX using adjusted hazard ratios (HRs) with stratification factors; performance status and unresectable or recurrent (+adjuvant chemotherapy) disease. RESULTS: Overall, 685 patients were randomized from January 2010 to October 2011. In per-protocol population, SOX (n = 318) was noninferior to CS (n = 324) in PFS [median, 5.5 versus 5.4 months; HR 1.004, 95% confidence interval (CI) 0.840-1.199; predefined noninferiority margin 1.30]. The median OS for SOX and CS were 14.1 and 13.1 months, respectively (HR 0.958 with 95% CI 0.803-1.142). In the intention-to-treat population (SOX, n = 339; CS, n = 337), the HRs in PFS and OS were 0.979 (95% CI 0.821-1.167) and 0.934 (95% CI 0.786-1.108), respectively. The most common ≥grade 3 adverse events (SOX versus CS) were neutropenia (19.5% versus 41.8%), anemia (15.1% versus 32.5%), hyponatremia (4.4% versus 13.4%), febrile neutropenia (0.9% versus 6.9%), and sensory neuropathy (4.7% versus 0%). CONCLUSION: SOX is as effective as CS for AGC with favorable safety profile, therefore SOX can replace CS. CLINICAL TRIAL NUMBER: JapicCTI-101021.

Randomised phase II study of S-1/cisplatin plus TSU-68 vs S-1/cisplatin in patients with advanced gastric cancer.

BACKGROUND: This study aimed to determine whether combination S-1 plus cisplatin (CDDP) therapy, the most widely used therapy for Japanese patients with advanced gastric cancer, and the novel oral antiangiogenic agent TSU-68 could contribute to gastric cancer treatment. METHODS: Ninety-three patients with chemotherapy-naïve unresectable or recurrent advanced gastric cancers were randomised into two groups: TSU-68 plus S-1/CDDP (group A) and S-1/CDDP (group B) groups. Both patient groups received identical S-1 and CDDP dosages. TSU-68 was orally administered for 35 consecutive days. Group B patients received S-1 orally twice daily for three consecutive weeks, followed by intravenous CDDP on day 8. The primary endpoint was progression-free survival (PFS). RESULTS: Median PFS periods were 208 and 213 days in groups A and B, respectively (P=0.427). Median survival periods for groups A and B were 497.0 and 463.5 days, respectively (P=0.219). No statistically significant differences were noted for PFS, survival or the adverse event (AE) incidence rate. All AEs were expected according to previous reports for TSU-68, TS-1, and CDDP. CONCLUSION: Combination therapy involving TSU-68, S-1, and CDDP was safe and well tolerated in patients with chemotherapy-naïve unresectable or recurrent advanced gastric cancers. However, factors related to therapeutic efficacy should be investigated further.

KRAS mutations in primary tumours and post-FOLFOX metastatic lesions in cases of colorectal cancer.

BACKGROUND: KRAS mutations are predictive markers for the efficacy of anti-EGFR antibody therapies in patients with metastatic colorectal cancer. Although the mutational status of KRAS is reportedly highly concordant between primary and metastatic lesions, it is not yet clear whether genotoxic chemotherapies might induce additional mutations. METHODS: A total of 63 lesions (23 baseline primary, 18 metastatic and 24 post-treatment metastatic) from 21 patients who were treated with FOLFOX as adjuvant therapy for stage III/IV colorectal cancer following curative resection were examined. The DNA samples were obtained from formalin-fixed paraffin-embedded specimens, and KRAS, NRAS, BRAF and PIK3CA mutations were evaluated. RESULTS: The numbers of primary lesions with wild-type and mutant KRAS codons 12 and 13 were 8 and 13, respectively. The mutational status of KRAS remained concordant between the primary tumours and the post-FOLFOX metastatic lesions, irrespective of patient background, treatment duration and disease-free survival. Furthermore, the mutational statuses of the other genes evaluated were also concordant between the primary and metastatic lesions. CONCLUSION: Because the mutational statuses of predictive biomarker genes were not altered by FOLFOX therapy, specimens from both primary tumours and post-FOLFOX tumour metastases might serve as valid sources of DNA for known genomic biomarker testing.

Phase I first-in-human study of TAK-285, a novel investigational dual HER2/EGFR inhibitor, in cancer patients.

BACKGROUND: This phase I first-in-human study was conducted in Japanese patients to investigate the safety, pharmacokinetics (PKs), and determine the maximum tolerated dose (MTD) of oral TAK-285, a novel dual erbB protein kinase inhibitor that specifically targets human epidermal growth factor receptor (EGFR) and HER2. METHODS: The TAK-285 dose was escalated until MTD was determined. A second patient cohort received TAK-285 at the MTD for at least 4 weeks. RESULTS: In all, 26 patients received TAK-285 at doses ranging from 50 to 400 mg once daily (q.d.) or twice daily (b.i.d.); 20 patients made up the dose escalation cohort and the remaining 6 patients were the repeated administration cohort. TAK-285 was well tolerated. Dose-limiting toxicities noted in two patients who received 400 mg b.i.d. were grade 3 increases in aminotransferases and grade 3 decreased appetite. Consequently, the MTD was determined to be 300 mg b.i.d. Absorption of TAK-285 was rapid after oral dosing, and plasma exposure at steady-state increased in a dose-proportional fashion for doses ranging from 50 to 300 mg b.i.d. A partial response was observed for one patient with parotid cancer who received 300 mg b.i.d. CONCLUSION: The toxicity profile and PK properties of oral TAK-285 warrant further evaluation.

KRAS mutations detected by the amplification refractory mutation system-Scorpion assays strongly correlate with therapeutic effect of cetuximab.

BACKGROUND: We aimed to compare the sensitive and quality-controlled KRAS testing with direct sequencing and to assess the impact on decision making of treatment. PATIENTS AND METHODS: We analysed genomic DNA isolated from macrodissected formalin-fixed paraffin-embedded specimens by direct sequencing and an amplification refractory mutation system-Scorpion assay (ARMS/S) method. Cetuximab was administered to patients identified as having wild-type (WT) KRAS using direct sequencing. Therapeutic effects were evaluated according to their KRAS status as determined by ARMS/S. RESULTS: Among the 159 patients, the overall mutation rate was determined to be 37.0% by direct sequencing and 44.0% by ARMS/S. For the patients diagnosed as WT by direct sequencing and treated with cetuximab (n=47), a response rate of 16.0% was observed for 38 ARMS/S WT patients, whereas 9 ARMS/S mutant (MUT) patients failed to respond. The ARMS/S WT patients showed significant improvement in progression-free survival (PFS) and overall survival (OS) compared with ARMS/S MUT patients (PFS median 5.0 vs 1.7 months, hazards ratio (HR)=0.29, P=0.001; OS median 12.1 vs 3.8 months, HR=0.26, P=0.001). CONCLUSION: Sensitive and quality-controlled KRAS testing may provide improved predictive power to determine the efficacy of anti-epidermal growth factor antibodies.

Feasibility study of adjuvant chemotherapy with S-1 plus cisplatin for gastric cancer.

PURPOSE: To evaluate the feasibility of S-1 plus cisplatin as adjuvant chemotherapy for stage III gastric cancer after curative resection. METHODS: Japanese patients with stage III gastric cancer who underwent gastrectomy with D2 lymph node resection were enrolled. Treatment consisted of 3 cycles of S-1 (80 mg/m(2)/day, b.i.d.) for 21 days followed by a 14-day rest, and cisplatin (60 mg/m(2) iv) on day 8. After that, S-1 monotherapy was given on days 1-28 every 6 weeks until 1-year postsurgery. After protocol amendment, the first chemotherapy cycle consisted of S-1 monotherapy; cisplatin was added to cycles 2, 3, and 4, followed by S-1 monotherapy up to 1-year postsurgery. The primary endpoint was the completion rate of three cycles of S-1 plus cisplatin. RESULTS: A total of 63 enrolled patients have been evaluated. Grade 3/4 toxicities included neutropenia (40%), anorexia (28%), and febrile neutropenia (4%) before protocol amendment (n = 25), and neutropenia (37%), anorexia (8%), and febrile neutropenia (3%) after amendment implementation (n = 38). Excluding ineligible cases, treatment completion rates were 57% (12/21) before and 81% (30/37) after the protocol amendment. CONCLUSIONS: The amended S-1 plus cisplatin is more feasible than the original protocol because of early dose reduction of S-1 prior to cisplatin addition and greater recovery time from surgery prior to cisplatin. This treatment should be considered as a feasible experimental arm for the next postoperative adjuvant phase III trial.

Phase I trial of combination chemotherapy with docetaxel, cisplatin and S-1 (TPS) in patients with locally advanced or recurrent/metastatic head and neck cancer.

BACKGROUND: we investigated the maximum tolerated dose (MTD) of combination therapy with docetaxel, cisplatin, and S-1 (TPS) in patients with locally advanced or recurrent/metastatic head and neck cancer (HNC). PATIENTS AND METHODS: treatment consisted of docetaxel (Taxotere) at doses of 50, 60, and 70 mg/m(2); cisplatin at 70 mg·m(2)/day on day 1; and S-1 twice daily on days 1-14 at doses of 40, 60, and 80 mg·m(2)/day, repeated every 3 or 4 weeks. RESULTS: forty patients were enrolled. MTD was not reached until level 4. Subjects at expanded dose were limited to patients with locally advanced disease. Two dose-limiting toxic effects (DLTs) were observed at dose level 5 (TPS: 70/70/80 mg·m(2)/day, every 3 weeks), namely one grade 3 infection and one grade 3 hyperbilirubinemia, establishing this as the MTD. Of 12 patients treated at dose level 6 (TPS: 70/70/60 mg·m(2)/day, every 3 weeks), 2 DLTs were seen. Six achieved a complete response and 22 a partial response, giving a response rate of 70%. CONCLUSIONS: TPS was well tolerated. The recommended phase II dose as induction chemotherapy for locally advanced HNC was determined as 70/70/60 mg·m(2)/day every 3 weeks. Antitumor activity was highly promising and warrants further investigation.

Phase 1 study of conatumumab, a pro-apoptotic death receptor 5 agonist antibody, in Japanese patients with advanced solid tumors.

PURPOSE: Conatumumab is a fully human monoclonal agonist antibody against human death receptor 5 (DR5). The primary objectives of this phase 1 study were to assess the safety, tolerability, and pharmacokinetics (PK) of conatumumab in Japanese patients with advanced solid tumors. METHODS: This is an open-label ascending dose study with a starting dose level of 3 mg/kg. Subsequent doses of 10 and 20 mg/kg were planned. Six patients were enrolled into 1 of 3 dose cohorts (3, 10, or 20 mg/kg) of conatumumab administered intravenously once every 2 weeks as a single agent. No conatumumab was administered on day 43 to allow the assessment of terminal PK parameters. The primary endpoints were the incidence of dose-limiting toxicities (DLTs) and assessment of PK parameters of conatumumab. RESULTS: Eighteen patients received at least 1 dose of conatumumab. There were no DLTs observed as defined in the protocol. No patients had an adverse event leading to conatumumab discontinuation. Conatumumab demonstrated dose-linear kinetics. A best response of stable disease was reported in nine patients. Monocytes were found to express DR5 and showed a high degree of conatumumab receptor occupancy after treatment at all dose levels. CONCLUSIONS: Conatumumab administered up to 20 mg/kg once every 2 weeks was well tolerated in Japanese patients with advanced solid tumors. Adverse events and PK in these patients were similar to those in the first in human (FIH) study.

Clinical features of interstitial lung disease induced by standard chemotherapy (FOLFOX or FOLFIRI) for colorectal cancer.

BACKGROUND: Chemotherapy-induced interstitial lung disease (ILD) in colorectal cancer (CRC) patients is rarely reported, but its clinical features remain to be clarified. PATIENTS AND METHODS: Using a computerized database, we retrospectively identified patients who developed ILD from 734 patients with CRC treated with infusional 5-fluorouracil, leucovorin and oxaliplatin (FOLFOX) or infusional 5-fluorouracil, leucovorin and irinotecan (FOLFIRI) from April 2005 to December 2008 at the National Cancer Center Hospital East. RESULTS: Of 734 patients, 11 patients developed ILD (1.5%) and 4 of those patients died (0.54%). Of the 11 patients, 10 showed pulmonary shadows other than lung metastases before chemotherapy. ILD developed during FOLFOX in six patients, at 137 days after completion of FOLFOX in one patient, during oxaliplatin interruption of FOLFOX in one patient and during FOLFIRI in the remaining three patients. FOLFOX had been administered at some point for all ILD patients, with a median of 10 cycles (range 2-17 cycles) and a median dose of administered oxaliplatin of 850 mg/m(2) (range 170-1445 mg/m(2)). CONCLUSIONS: ILD following FOLFOX or FOLFIRI is an uncommon but life-threatening complication. Care must be taken regarding the onset of ILD, not only during but also after chemotherapy for CRC.

Phase II study of oxaliplatin plus S-1 as first-line treatment for advanced gastric cancer (G-SOX study).

BACKGROUND: The efficacy and safety of oxaliplatin combined with S-1 (SOX regimen) for unresectable advanced or recurrent gastric cancer were investigated. PATIENTS AND METHODS: Oxaliplatin was administered i.v. (100 mg/m(2)) on day 1, while S-1 was administered orally (80 mg/m(2)/day, b.i.d.) for 14 days followed by a 7-day rest. This schedule was repeated every 3 weeks. RESULTS: Among 55 patients enrolled, one patient received oxaliplatin for the other study, and three patients were considered unsuitable against the inclusion criteria. Accordingly, 51 patients were assessable for efficacy. The response rate was 59%, and the disease control rate was 84%. The median progression-free survival time was 6.5 months, the 1-year survival rate was 71%, and the median survival time was 16.5 months. In 54 patients assessed for safety, the major grade 3/4 toxic effects were neutropenia (22%), thrombocytopenia (13%), anemia (9%), anorexia (6%), fatigue (6%), and sensory neuropathy (4%). CONCLUSION: These findings indicate that SOX regimen with oxaliplatin at a dose of 100 mg/m(2) is feasible and shows promising efficacy against advanced gastric cancer.

Treatment of a Gilbert's syndrome patient with irinotecan, leucovorin and 5-fluorouracil.

The patient was an elderly male who had radical surgery for sigmoid cancer in 2001. Owing to metastasis of his cancer to the left supraclavicular lymph nodes in 2002, the patient was admitted to our hospital for systemic chemotherapy. We started treatment with irinotecan, leucovorin, 5-fluorouracil (IFL). After administering 100 mg/m2 of irinotecan, 250 mg/m2 leucovorin and 600 mg/m2 5-fluorouracil to the patient on day 1, grade 3 leukopenia developed rapidly and grade 4 thrombocytopenia was observed on day 5. We excluded irinotecan from the medication and continued the administration of 5-fluorouracil and leucovorin, but his tumors had not been reduced sufficiently. Based on some examination results, we assumed that the patient had Gilbert's syndrome and that the severe side effects that occurred were due to prolongation of SN38 metabolism. We again administered irinotecan but at reduced dose (25 mg/m2). Four courses of this modified IFL were administered safely and the response was favorable.

Intraocular hemangiopericytoma. A case report.

A 55-year-old man presented with a smoothly elevated solid choroidal mass with choroidal detachment in the temporal region of the left eye. Both fluorescein and indocyanine green angiography suggested a vascularized lesion such as an angioma. However, radiographic examination revealed a solid, circumscribed, dome-shaped mass. During a 3-month observation, the mass gradually enlarged and invaded the iris. The possibility of malignant melanoma could not be ruled out. Due to rapid and continued growth of the tumor, the eye was enucleated. Histopathologic examination revealed proliferation of spindle-shaped cells surrounding reticulin-positive vessels, which is characteristic of hemangiopericytoma. To our knowledge, this is only the fourth reported case of intraocular hemangiopericytoma and the first diagnosed in a male patient.

Auto iris pigment epithelial cell transplantation in patients with age-related macular degeneration: short-term results.

Autologous iris pigment epithelial cell transplantation was performed on patients with exudative age-related macular degeneration (AMD). Autologous IPE cell culture was performed using autologous serum after iridectomy in 7 patients with AMD. The cell suspensions (2 approximately 20 x 10(4) cells) were transplanted into the submacular lesion of individuals after removal of neovascular membranes. Subsequent ophthalmological examinations, including best corrected visual acuity and fluorescein or indocyanine green angiography, were performed. In addition, 15 patients with AMD, who underwent removal of neovascular membrane without transplantation, were evaluated as non randomized controls. Varying degrees of atrophy or defects of choriocapillaris and retinal pigment epithelium were observed in all of the patients. No cystoid macular edema or fluorescein leakage was observed after treatment, but window defects were present. No patient had decreased visual acuity. One treated patient developed mild subretinal fibrosis and an other patient developed mild preretinal fibrosis, however no difference was significant when compared with the control. In conclusion, the treatment resulted in no significant improvement in macular function, as compared with the control; however, no rejection or deterioration in visual acuity occurred up to the 13 month follow up.

mRNA expression of proto-oncogenes and platelet-derived growth factor in proliferative vitreoretinal diseases.

PURPOSE: To detect the expression of mRNA of protooncogenes ets-1, c-jun, c-fos, and platelet-derived growth factor (PDGF) in proliferative membranes of patients with proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). METHODS: cDNA was synthesized from mRNA of proliferative membranes from patients with PDR, PVR, premacular fibrosis (PMF), acute retinal necrosis (ARN), and age-related macular degeneration (ARMD). Ets-1, c-jun, c-fos, PDGF-A, and PDGF-B cDNA were amplified using reverse transcriptase-polymerase chain reaction (PCR). RESULTS: Proto-oncogene mRNA was highly expressed in membranes from patients with severe PDR, grade D PVR. PDGF mRNA was expressed in almost all samples. CONCLUSIONS: Our results suggest that not only PDGF mRNA was expressed in the membranes of patients with PDR and PVR, but proto-oncogenes ets-1, c-jun, and c-fos mRNA were also expressed.

Structural organization of the human microphthalmia-associated transcription factor gene containing four alternative promoters.

Microphthalmia-associated transcription factor (MITF) affects the development of many types of cells, including melanocytes and retinal pigment epithelium (RPE). MITF consists of at least three isoforms, MITF-A, MITF-H and MITF-M, differing at their amino-termini and expression patterns. Here, we characterize the structural organization of the human MITF gene. The gene contains at least four isoform-specific first exons, exons 1A, 1H, 1B and 1M in the 5' to 3' direction, each of which encodes the unique amino-terminus of a given isoform, including newly identified MITF-B. The 5'-flanking regions of these isoform-specific exons are termed promoters A, H, B and M, respectively, which showed different promoter activities, as judged by transient transfection assay. Promoter A directs the expression of a reporter gene in RPE, cervical cancer and melanoma cells, whereas promoter M is functional only in melanoma cells. Promoter H showed the significant activity in RPE and cervical cancer cells but not in melanoma cells. In contrast, the 1.7 kb 5'-flanking region of exon 1B showed no noticeable promoter activity in these cell lines. Therefore, alternative promoters provide the MITF gene with the diversity in transcriptional regulation and the capability of generating structurally different protein isoforms.

Implications of isoform multiplicity of microphthalmia-associated transcription factor in the pathogenesis of auditory-pigmentary syndromes.

Microphthalmia-associated transcription factor (MITF) is the human homolog of a basic helix-loop-helix-leucine zipper protein (Mitf), encoded by the mouse microphthalmia locus. Mutations in the MITF gene have been identified in some patients with Waardenburg syndrome type 2 (WS2), which is a dominantly inherited disorder, characterized by varying combinations of sensorineural hearing loss and pigmentary disturbances. Furthermore, mice with mutations at the Mitf locus are associated with various phenotypes, such as white coat color, small eyes, a deficiency in mast cells, and osteopetrosis. Thus, MITF/Mitf may play an important role in differentiation of melanocytes and some other cell types. Recently we have identified two MITF isoforms with extended amino-termini, MITF-A and MITF-H. Both isoforms possess unique amino-termini that are different from the amino-terminus of the originally identified melanocyte-specific MITF (MITF-M). MITF-M mRNA is exclusively expressed in melanocytes and pigmented melanoma cells, whereas MITF-A and MITF-H mRNA are widely expressed in many cell types, including retinal pigment epithelium. Transient transfection assays suggested that these isoforms possess differential transactivation capacity. It is therefore conceivable that the previously identified mutations may alter the functions of not only MITF-M but also MITF-A and MITF-H. Possible implications of the MITF isoform multiplicity in the pathogenesis of auditory-pigmentary disorders are discussed.

Cloning and characterization of a new exo-cellulase gene, cel3, in Irpex lacteus.

A new cellulose-inducible gene (named cel3) was isolated from a strain of the white rot basidiomycete, Irpex lacteus MC-2. The cel3 open reading frame, containing two introns, encodes a polypeptide of 526 amino acids residues with a molecular mass of 55794 Da. Expression of the cel3 gene was induced by various insoluble celluloses and CM-cellulose. Transcription of cel3 was abolished when cells were cultivated in media containing the above cellulosic substrates, but added with glucose, fructose or lactose, while addition of glycerol or mannitol did not affect the cel3 mRNA level. The amino acid sequence of the catalytic domain of the Cel3 protein was homologous to that of fungal exo-type cellulases belonging to family 7 of the glycosyl hydrolases. A phylogenetic study showed that these exo-type cellulases can be clearly separated from family 7 endo-type cellulases.

Functional analysis after auto iris pigment epithelial cell transplantation in patients with age-related macular degeneration.

Recent transplantation studies indicate that subretinal space is not always an immunologically privileged site and non-autologous cells may be rejected in patients with exudative age-related macular degeneration (AMD). We performed autologous iris pigment epithelial (IPE) cell transplantation by cell suspension after autologous IPE cell culture in 8 patients with AMD. These patients were followed without immunosuppression between 1.5 and 8 months and the retinal function was analyzed. No cystoid macular edema or fluorescein leakage was observed. Six of the 8 patients improved visual acuity of more than two lines and the other two patients retained preoperative visual acuity. Five patients had increased visual field sensitivity, one patient retained pretransplantation sensitivity, and one patient showed a gradual decrease in sensitivity (one patient was not examined). Although 2 of the 8 patients showed decreased amplitude of flicker electroretinography (ERG) (about 60 to 70% as that of preoperative level), the average improvement of each amplitude of a single white flash (a wave), photopic, or flicker ERG was 123, 102, and 107%, respectively. No proliferative change in the submacular lesion or vitreous cavity was observed after transplantation. From this functional analysis, transplanted autologous IPE may have, in part, an alternative function in regard to the retinal pigment epithelium in the subretinal space.

Isolation and transcriptional analysis of a cellulase gene (cell) from the basidiomycete Irpex lacteus.

A gene (named cell) homologous to the cellobiohydrolase I gene (cbhl) of Trichoderma reesei was isolated and sequenced from the white rot basidiomycete Irpex lacteus MC-2. The cell open reading frame consists of 1551 bp, which is interrupted by two introns, encoding a polypeptide of 517 amino acid residues with a calculated molecular mass of 54,522 Da. The deduced amino acid sequence showed that CEL1 (the protein encoded by cell) has a modular structure consisting of a catalytic domain of 449 amino acids and a C-terminal cellulose-binding domain (CBD) of 36 amino acids separated by a proline-, serine-, threonine-rich linker region of 32 amino acids. The CEL1 catalytic domain is homologous with fungal cellobiohydrolases (CBHs) belonging to family 7 of the glycosyl hydrolases. The transcription of cell was induced in the presence of various cellulosic substrates and repressed by glucose. It was therefore concluded that the reported sequence represents the first cellulase gene isolated from the basidiomycete Irpex.

A big gene linked to small eyes encodes multiple Mitf isoforms: many promoters make light work.

Among more than 80 different loci related to mouse coat color, microphthalmia-associated transcription factor (Mitf) encoded at the mouse microphthalmia locus is one of the most exciting molecules that regulates the development and survival of many cell types, including melanocyte, retinal pigment epithelium (RPE), and mast cells. Mitf and its human homolog MITF consist of at least three isoforms, referred to as Mitf-A/MITF-A, the heart-type Mitf-H/MITF-H, and the melanocyte lineage-specific Mitf-M/MITF-M, respectively. These isoforms differ in the amino-terminal domains but share a transactivation domain and a basic helix-loop-helix and leucine-zipper structure that is required for DNA binding and dimerization. MITF-M is exclusively expressed in melanocytes and melanoma cells, but not in other cell types, including RPE cells. In contrast, MITF-A mRNA is widely expressed in many cell types. These three isoform mRNAs are possibly generated by differential usage of the gene promoters and by alternative splicing. We predict that the entire MITF gene spans about 200 kb of DNA. Like MITF-M, MITF-A is able to activate the two melanogenesis gene promoters, tyrosinase and tyrosinase-related protein 1. These results suggest that melanogenesis may be regulated by different MITF isoforms in melanocyte and RPE. Possible implications of the multiplicity in Mitf/MITF isoforms are discussed.