RESUMO
BACKGROUND: Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm with intermediate malignant potential. Although most often seen in the lungs, it can occur at multiple anatomical locations, including the gastrointestinal tract. An esophageal lesion is extremely rare, however. IMTs present most commonly in children and young adults. The main therapeutic approach is surgical resection. CASE REPORT: We report on the follow-up of a case in a 13-year-old boy with IMT in the esophagus. He underwent surgical resection in 2013 and is free of disease to date. CONCLUSION: Surgical resection is the most preferred therapy. If the resection is complete, the risk of recurrence is low. Nevertheless, every patient should be carefully followed up after the resection.
Assuntos
Neoplasias Esofágicas/cirurgia , Neoplasias de Tecido Muscular/cirurgia , Adolescente , Neoplasias Esofágicas/etiologia , Neoplasias Esofágicas/patologia , Humanos , Masculino , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/patologiaRESUMO
Inflammatory myofibroblastic tumours (IMTs) are rare tumours with unpredictable biological behaviour ranging from benign to locally invasive and rarely, distant metastasis. While neurofibromatosis type 1 (NF1) may manifest with gastrointestinal soft tissue tumours, this is the first report in the literature that describes an IMT occurring in a NF1 patient who presented with intestinal obstruction. Our patient presented with intestinal obstruction secondary to an obstructing terminal ileum mesenteric tumour. En bloc bowel resection was performed, with histology revealing an IMT and an adjacent neurofibroma. The resection margins were clear and the patient was free of recurrence at six months.
Assuntos
Obstrução Intestinal/etiologia , Mesentério/patologia , Neoplasias de Tecido Muscular/diagnóstico , Neurofibromatose 1/complicações , Neoplasias Peritoneais/diagnóstico , Humanos , Obstrução Intestinal/cirurgia , Masculino , Mesentério/diagnóstico por imagem , Mesentério/imunologia , Mesentério/cirurgia , Pessoa de Meia-Idade , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/imunologia , Neoplasias de Tecido Muscular/cirurgia , Neoplasias Peritoneais/etiologia , Neoplasias Peritoneais/imunologia , Neoplasias Peritoneais/cirurgia , Tomografia por Raios X , Resultado do TratamentoRESUMO
RATIONALE: Inflammatory myofibroblastic tumor (IMT) is an uncommon mesenchymal neoplasm, and its presence in a grafted liver is exceedingly rare. PATIENT CONCERNS: A 54-year-old woman was admitted to our hospital with a half-month history of intermittent melena. She had undergone deceased-donor liver transplantation (LT) for hepatitis B virus related liver cirrhosis without hepatocellular carcinoma 5 months previously. DIAGNOSIS: Laboratory examination showed impaired liver and renal functions and Epstein-Barr virus (EBV) infection, but tumor markers within normal ranges. Gastroscopy showed esophageal varices. Ultrasound and computed tomography angiography revealed an ill-defined and irregular solitary lesion in the porta hepatis, encasing both the portal vein and the hepatic artery. The lesion was characterized by arterial hyper-enhancement and hypo-enhancement in the remaining phases with contrast-enhanced ultrasound (CEUS). The lesion was finally confirmed as an IMT by ultrasound-guided biopsy. INTERVENTION: The patient received conservative treatment, including immunosuppression, endoscopic variceal ligation, antibiotics, steroids, and antiviral agents. OUTCOME: The patient's gastrointestinal bleeding was controlled, but the symptoms associated with portal hypertension worsened. Attempts to perform a transjugular intrahepatic portosystemic shunt were unsuccessful, and she unfortunately died soon after. LESSONS: A differential diagnosis of IMT should be considered in LT recipients presenting with EBV infection, normal tumor markers, and a de novo hepatic lesion with quick wash-in and wash-out on CEUS. Ultrasound is associated with the advantages of convenience and nonionizing radiation, and should thus be the priority approach for monitoring transplanted liver.
Assuntos
Neoplasias Hepáticas/etiologia , Transplante de Fígado/efeitos adversos , Neoplasias de Tecido Muscular/etiologia , Feminino , Hemorragia Gastrointestinal/etiologia , Hemorragia Gastrointestinal/terapia , Humanos , Neoplasias Hepáticas/complicações , Pessoa de Meia-Idade , Neoplasias de Tecido Muscular/complicaçõesRESUMO
Inflammatory myofibroblastic tumors (IMTs) are rare tumors with an intermediate spectrum of biological behavior. IMTs are uncommon secondary malignancies after hematopoietic stem cell transplant. The presence of anaplastic lymphoma kinase rearrangements in 50% of IMTs has led to therapeutic trials with crizotinib, although limited experience remains with crizotinib use in children. We describe the first reported case of a highly aggressive and metastatic IMT (secondary malignancy) in an 8-year-old girl following umbilical cord blood transplant. Although tumor response was demonstrated with anaplastic lymphoma kinase inhibition, she later developed fatal pulmonary toxicity from diffuse alveolar damage, a feature felt most likely to be due to crizotinib.
Assuntos
Transplante de Células-Tronco de Sangue do Cordão Umbilical/efeitos adversos , Lesão Pulmonar/induzido quimicamente , Neoplasias de Tecido Muscular/tratamento farmacológico , Neoplasias de Tecido Muscular/etiologia , Pirazóis/toxicidade , Piridinas/toxicidade , Quinase do Linfoma Anaplásico , Crizotinibe , Evolução Fatal , Feminino , Humanos , Lactente , Neoplasias de Tecido Muscular/complicações , Segunda Neoplasia Primária , Inibidores de Proteínas Quinases , Pirazóis/administração & dosagem , Piridinas/administração & dosagem , Receptores Proteína Tirosina Quinases/antagonistas & inibidoresRESUMO
The complications related to the retropubic placement of polypropylene mesh (TVT) for stress urinary incontinence have been extensively described in the literature. The occurrence of an inflammatory myofibroblastic tumor, however, has not been previously reported as a complication of placement of a mesh sling. We report such a case in a patient with neurofibromatosis who had undergone a TVT for stress urinary incontinence and present a brief review of the literature.
Assuntos
Neoplasias de Tecido Muscular/etiologia , Slings Suburetrais/efeitos adversos , Neoplasias da Bexiga Urinária/etiologia , Incontinência Urinária por Estresse/cirurgia , Feminino , Humanos , Pessoa de Meia-Idade , Neoplasias de Tecido Muscular/patologia , Neoplasias de Tecido Muscular/cirurgia , Neoplasias da Bexiga Urinária/patologia , Neoplasias da Bexiga Urinária/cirurgia , Incontinência Urinária por Estresse/patologiaAssuntos
Anti-Inflamatórios/uso terapêutico , Neoplasias Hepáticas/tratamento farmacológico , Neoplasias de Tecido Muscular/tratamento farmacológico , Esteroides/uso terapêutico , Humanos , Lactente , Inflamação/complicações , Inflamação/diagnóstico , Inflamação/tratamento farmacológico , Neoplasias Hepáticas/complicações , Neoplasias Hepáticas/etiologia , Neoplasias de Tecido Muscular/complicações , Neoplasias de Tecido Muscular/etiologia , Indução de Remissão/métodos , Carga Tumoral/efeitos dos fármacosRESUMO
Epstein-Barr virus associated smooth muscle cell tumors are commonly found in immunocompromised patients. These tumors occur most commonly in patients with AIDS and with greater incidence in children. The incidence of gallbladder tumors in these patients is rare, however. We report the case of a 10-year-old female patient who presented to our unit. She is HIV positive and on antiretroviral treatment. She required an emergency cholecystectomy to relieve external compression of the common bile duct where an empyematous gallbladder was found. Histopathology confirmed the presence of an Epstein-Barr virus-associated smooth muscle tumor. She is noted to have other asymptomatic lesions. Surgical intervention is reserved for symptomatic lesions and improves the immunocompromised state, although there is a propensity for local recurrence of the tumor.
Assuntos
Síndrome da Imunodeficiência Adquirida/complicações , Infecções por Vírus Epstein-Barr/complicações , Neoplasias da Vesícula Biliar/etiologia , Neoplasias Primárias Múltiplas/etiologia , Neoplasias de Tecido Muscular/etiologia , Dor Abdominal/etiologia , Síndrome da Imunodeficiência Adquirida/tratamento farmacológico , Ampola Hepatopancreática , Fármacos Anti-HIV/uso terapêutico , Criança , Colangiopancreatografia Retrógrada Endoscópica , Colangiopancreatografia por Ressonância Magnética , Colecistectomia , Neoplasias do Ducto Colédoco/etiologia , Emergências , Empiema/etiologia , Empiema/cirurgia , Feminino , Neoplasias da Vesícula Biliar/diagnóstico , Neoplasias da Vesícula Biliar/cirurgia , Herpesvirus Humano 4/patogenicidade , Humanos , Hospedeiro Imunocomprometido , Neoplasias de Tecido Muscular/diagnóstico , Neoplasias de Tecido Muscular/cirurgiaRESUMO
Inflammatory myofibroblastic tumor (IMT) occurs infrequently in the liver. It is controversial whether it represents a low grade mesenchymal neoplasm or a reactive inflammatory lesion. Local recurrence and metastasis are rare and some tumors are associated with infectious agents. We report on a case of a large and partially resected IMT with local recurrence and diaphragm and kidney infiltration detected on routine surveillance two years later. Histologically, the tumor showed spindle cells without atypia, mitosis or necrotic areas in a myxoid and collagenized background with inflammatory cells. In the liver portal tracts, granulomatous lesions with viable eggs of Schistosoma mansoni were identified. Immunohistochemistry demonstrated spindle cells which were smooth-muscle actin and vimentin positive. In conclusion, this case points out that these histological patterns do not predict the aggressive biological behavior of the lesion. A reason for the recurrence and the infiltration may be incomplete tumor resection. Further investigation is necessary in order to better clarify an infectious cause in some IMTs.
Assuntos
Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/etiologia , Neoplasias de Tecido Muscular/diagnóstico , Neoplasias de Tecido Muscular/etiologia , Esquistossomose/complicações , Esquistossomose/diagnóstico , Adulto , Animais , Feminino , Humanos , Fígado/parasitologia , Neoplasias Hepáticas/cirurgia , Recidiva Local de Neoplasia/diagnóstico , Neoplasias de Tecido Muscular/cirurgia , Reoperação , Schistosoma mansoni/isolamento & purificaçãoAssuntos
Eosinofilia/complicações , Esofagite/complicações , Neoplasias Gastrointestinais/patologia , Neoplasias Gastrointestinais/cirurgia , Neoplasias de Tecido Muscular/patologia , Neoplasias de Tecido Muscular/cirurgia , Dor Abdominal/etiologia , Adulto , Anemia/etiologia , Emergências , Endoscopia do Sistema Digestório , Feminino , Neoplasias Gastrointestinais/etiologia , Hematemese/etiologia , Humanos , Imuno-Histoquímica , Neoplasias de Tecido Muscular/etiologiaRESUMO
Inflammatory myofibroblastic tumor (IMT) is a rare tumor with a particular histological pattern of myofibroblasts and mixed inflammatory infiltrate. IMT has been rarely described in association with malignancy. This case report is of a 16-year-old male who had Hodgkin's disease (stage IVA) and who after chemotherapy and radiotherapy developed IMT, 16 months post completion of therapy. The IMT was in the lung in an area which was previously involved with HD and had undergone radiotherapy. PET imaging with F(18)FDG was used in the initial diagnosis and has been used in follow-up after full surgical resection of the lesion.
Assuntos
Fibrossarcoma/diagnóstico , Doença de Hodgkin/complicações , Neoplasias Pulmonares/diagnóstico , Neoplasias de Tecido Muscular/diagnóstico , Tomografia por Emissão de Pósitrons/métodos , Adolescente , Diagnóstico Diferencial , Fibrossarcoma/etiologia , Fibrossarcoma/cirurgia , Seguimentos , Doença de Hodgkin/diagnóstico , Humanos , Neoplasias Pulmonares/etiologia , Neoplasias Pulmonares/cirurgia , Masculino , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/cirurgia , Pneumonectomia , Tomografia Computadorizada por Raios XRESUMO
Vascular smooth muscle tumors are very rare. They can be benign or malign. Intravascular leiomyomatosis is a benign neoplasm that extends through the veins and caries significant morbidity. Angioleiomyoma is a benign neoplasm of the extremities that caries minimal morbidity. Vascular leiomyosarcomas are malign neoplasms derived from vascular smooth cells. They are usually localized to the inferior vena cava, but can also arise from the pulmonary arteries or veins or other peripheral vessels. This study reviews literature for epidemiology, clinical presentation, diagnosis and management of patients with vascular smooth muscle tumors.
Assuntos
Neoplasias de Tecido Muscular/diagnóstico , Neoplasias de Tecido Muscular/terapia , Neoplasias Vasculares/diagnóstico , Neoplasias Vasculares/terapia , Quimioterapia Adjuvante , Diagnóstico por Imagem , Humanos , Neoplasias de Tecido Muscular/epidemiologia , Neoplasias de Tecido Muscular/etiologia , Radioterapia Adjuvante , Neoplasias Vasculares/epidemiologia , Neoplasias Vasculares/etiologiaRESUMO
Inflammatory myofibroblastic tumor (IMT) is clinically and histologically characterized by inflammation. Some populations of IMT have anaplastic large cell lymphoma kinase (ALK) gene rearrangements. Infection with Epstein-Barr virus (EBV) and human herpesvirus-8 (HHV-8) in tumor cells of IMT has been reported; these reports, however, have been limited to ALK-negative IMT. The purpose of the present paper was to evaluate 21 cases of IMT for the presence of EBV and HHV-8. Immunohistochemically, 15 cases were ALK positive and six were negative. Of eight cases analyzed using reverse transcription-polymerase chain reaction, tropomyosin 3 (TPM3)-ALK, TPM4-ALK and clathrin heavy chain-ALK fusion genes were detected in one, two and two cases, respectively. All 21 IMT, irrespective of ALK expression, were negative for EBV by in situ hybridization for EBV-encoded RNA and immunohistochemical stain for latent membrane antigen-1. HHV-8 was also negative in all IMT by PCR for HHV-8 DNA sequence (KS330/233) and immunohistochemical stain for latent nuclear antigen. These results suggest that IMT may be a heterogeneous group in terms of pathogenesis, and EBV and HHV-8 do not play a major role in the pathogenesis of ALK-positive tumor.
Assuntos
Infecções por Vírus Epstein-Barr/complicações , Infecções por Herpesviridae/complicações , Herpesvirus Humano 4/patogenicidade , Herpesvirus Humano 8/patogenicidade , Neoplasias de Tecido Muscular/genética , Neoplasias de Tecido Muscular/virologia , Proteínas Tirosina Quinases/genética , Adolescente , Adulto , Idoso , Quinase do Linfoma Anaplásico , Antígenos Virais/genética , Antígenos Virais/metabolismo , Criança , Pré-Escolar , Cadeias Pesadas de Clatrina/genética , Cadeias Pesadas de Clatrina/metabolismo , Infecções por Vírus Epstein-Barr/genética , Infecções por Vírus Epstein-Barr/patologia , Feminino , Regulação Neoplásica da Expressão Gênica/genética , Regulação Viral da Expressão Gênica , Infecções por Herpesviridae/genética , Infecções por Herpesviridae/patologia , Herpesvirus Humano 4/genética , Herpesvirus Humano 8/genética , Humanos , Lactente , Masculino , Pessoa de Meia-Idade , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/patologia , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas de Fusão Oncogênica/genética , Proteínas Tirosina Quinases/metabolismo , Receptores Proteína Tirosina Quinases , Tropomiosina/genética , Tropomiosina/metabolismoAssuntos
Infecções por Vírus Epstein-Barr/etiologia , Herpesvirus Humano 4/patogenicidade , Transplante de Rim , Neoplasias Hepáticas/etiologia , Neoplasias de Tecido Muscular/etiologia , Adulto , Infecções por Vírus Epstein-Barr/terapia , Humanos , Neoplasias Hepáticas/terapia , Masculino , Neoplasias de Tecido Muscular/terapia , RNA Viral/análiseRESUMO
Recently some reports have suggested that gastrointestinal stromal tumors (GIST) might originate from the interstitial cells of Cajal or differentiate into them because they express c-kit and/or CD34 and indicated that the majority of previously diagnosed smooth muscle tumors (SMT) actually belong to GIST, but are not true SMT. We, therefore, detected c-kit, CD34, SMA, and S-100 in 106 Chinese cases of gastrointestinal tumors, which were histopathologically diagnosed as smooth muscle tumors originally, to demonstrate the immunophenotypes of these tumors. The results showed that 73 cases had immunoreaction with c-kit and/or CD34, of which 48 cases showed coexpression with either SMA or S-100 or with both. A correlation between the immunophenotypes and known histopathological parameters was also shown here based on follow-up data. We suggest that the concept of GIST should not be used as an umbrella to cover all gastrointestinal mesenchymal tumors, but be defined in a narrow term as differing from true smooth muscle tumors.
Assuntos
Sistema Digestório/patologia , Neoplasias Gastrointestinais/patologia , Músculo Liso/patologia , Neoplasias de Tecido Muscular/patologia , Células Estromais/patologia , Actinas/análise , Antígenos CD34/análise , Biomarcadores Tumorais/análise , Neoplasias Gastrointestinais/química , Neoplasias Gastrointestinais/etiologia , Humanos , Imuno-Histoquímica , Mitose , Músculo Liso/química , Músculo Liso/inervação , Neoplasias de Tecido Muscular/química , Neoplasias de Tecido Muscular/etiologia , Proteínas Proto-Oncogênicas c-kit/análise , Estudos Retrospectivos , Proteínas S100/análise , Células Estromais/químicaRESUMO
We reviewed the clinico-pathological features of a series of 13 cases of benign spindle stromal tumors (BSSTs) of the breast relating to a basic common theme consisting of a well-circumscribed proliferation of vimentin+/CD34+/BCL-2+/CD99+ spindly to oval-epithelioid cells, variably arranged in haphazard to short fascicular growth pattern, with interspersed thick or thin collagen bands. Morphological variations included atypical mono- or multi-nucleated cells in five cases and a mature lipomatous tumor component, varying from focal to prominent, in eight cases. Based on morphological and immunophenotypical features, a distinction was made between two main subtypes of these tumors--fibroblastic and myofibroblastic. The former subtype included two cases respectively represented by a typical solitary fibrous tumor (SFT) and a neoplasm labeled "spindle-cell lipoma (SCL)-like tumor", closely reminiscent of soft tissue SCL. Both tumors had cells with fibroblastic-like appearance, haphazardly arranged and immunoreactive for vimentin, CD34, BCL-2, and CD99. The latter subtype, comprised nine cases exhibiting evidence of myofibroblastic differentiation (desmin and alpha-smooth muscle actin) which were classified as myofibroblastomas (MFBs). The remaining two cases were defined as "mixed BSSTs", having typical features of diverse neoplasms, respectively represented by a case of MFB with focal SFT and pleomorphic/SCL-like areas, and SFT with focal MFB-like component. The common basic morpho-immunophenotypical features, the possibility that both fibroblastic and myofibroblastic tumors may contain an additional mature lipomatous component, and the existence of hybrid stages (mixed BSSTs) strongly support the view that such tumors belong to the same category of lesions. We postulate that the precursor of all these neoplasms is the vimentin+/CD34+ cells of the mammary stroma, the well-known inherent plasticity of which to differentiate toward several mesenchymal lines, provides the explanation for the phenotypic heterogeneity of these neoplasms. Accordingly, the encompassing term "benign spindle stromal tumors of the breast" is advocated for such tumors.
Assuntos
Neoplasias da Mama Masculina/patologia , Fibroma/patologia , Lipoma/patologia , Neoplasias de Tecido Muscular/patologia , Antígeno 12E7 , Idoso , Idoso de 80 Anos ou mais , Antígenos CD/análise , Antígenos CD34/análise , Biomarcadores Tumorais/análise , Neoplasias da Mama Masculina/química , Neoplasias da Mama Masculina/etiologia , Moléculas de Adesão Celular/análise , Feminino , Fibroma/química , Fibroma/etiologia , Humanos , Imuno-Histoquímica , Lipoma/química , Lipoma/etiologia , Masculino , Mamografia , Pessoa de Meia-Idade , Proteínas de Neoplasias/análise , Neoplasias de Tecido Muscular/química , Neoplasias de Tecido Muscular/etiologia , Proteínas Proto-Oncogênicas c-bcl-2/análise , Células Estromais/química , Células Estromais/patologia , Vimentina/análiseRESUMO
The AIDS epidemic continues unabated in Africa, Asia, and South America, and since patients survive longer, the number of chronically immunocompromised individuals is increasing in Europe and the United States. The number of children with HIV infection who will ultimately develop a malignancy is not known. Currently, tumors represent about 2% of the AIDS-defining events in children in the United States, but the incidence might be different in developing countries. The most common tumors in HIV-infected children are non-Hodgkin's lymphoma, smooth muscle tumors (leiomyosarcomas), and Kaposi's sarcoma (only in Africa). This article provides an overview of epidemiology and clinical and pathological presentations, as well as preliminary data regarding treatment options in children with HIV-associated malignancies.
Assuntos
Infecções por HIV/complicações , Transtornos Linfoproliferativos/etiologia , Neoplasias/etiologia , Antineoplásicos/uso terapêutico , Antivirais/uso terapêutico , Criança , Feminino , Doença de Hodgkin/tratamento farmacológico , Doença de Hodgkin/etiologia , Humanos , Hospedeiro Imunocomprometido , Linfoma não Hodgkin/diagnóstico , Linfoma não Hodgkin/tratamento farmacológico , Linfoma não Hodgkin/etiologia , Transtornos Linfoproliferativos/tratamento farmacológico , Masculino , Neoplasias/terapia , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/cirurgiaRESUMO
The purpose of this investigation was to study the incidence and size of smooth muscle tumors in several Japanese quail lines and to report recent correlated changes in mature BW and egg production. Laying females from lines selected solely (HW) or partly (HW-HP; HW-LP) for increased 4-wk BW or for decreased 4-wk BW (LW) and from the corresponding randombred control (R1) were used. Lines HW-HP and HW-LP were sublines of Line HW in which males were selected for increased 4-wk BW and females were selected for high or low level of total plasma phosphorus, respectively. Laying hens were examined for the presence of smooth muscle tumors after about 170 d of egg production (240 d of age). During Generations 19 through 26, mature BW was increasing in the HW line and decreasing in the LW line. Selection for either increased or decreased 4-wk BW resulted in decreased egg production, but the only significant change with generations was a decrease of 2.7 eggs per hen for a 120-d laying period in the LW line. Frequency and weight of the smooth muscle tumors were greater for females from the large-bodied lines than females from Line R1. No tumors were detected in LW females. Based on the linear regression of response on generations, tumor frequency was increasing in Line HW-LP but tumor weight was decreasing in this line. Tumor weight was increasing in the HW line. No other changes in tumor frequency or size were noted across generations. Weight of the tumors was not correlated with egg production. The presence of tumors did not seem to affect mortality during the laying period. The Japanese quail lines may serve as a useful animal model for the study of smooth muscle tumors in humans, chickens, and turkeys.
Assuntos
Doenças das Aves/etiologia , Coturnix , Neoplasias de Tecido Muscular/veterinária , Animais , Doenças das Aves/genética , Doenças das Aves/patologia , Peso Corporal/genética , Coturnix/anatomia & histologia , Coturnix/genética , Modelos Animais de Doenças , Feminino , Masculino , Neoplasias de Tecido Muscular/etiologia , Neoplasias de Tecido Muscular/patologiaRESUMO
The transplantation of cultured myoblasts into mature skeletal muscle is the basis for a new therapeutic approach to muscle and non-muscle diseases: myoblast-mediated gene therapy. The success of myoblast transplantation for correction of intrinsic muscle defects depends on the fusion of implanted cells with host myofibers. Previous studies in mice have been problematic because they have involved transplantation of established myogenic cell lines or primary muscle cultures. Both of these cell populations have disadvantages: myogenic cell lines are tumorigenic, and primary cultures contain a substantial percentage of non-myogenic cells which will not fuse to host fibers. Furthermore, for both cell populations, immune suppression of the host has been necessary for long-term retention of transplanted cells. To overcome these difficulties, we developed novel culture conditions that permit the purification of mouse myoblasts from primary cultures. Both enriched and clonal populations of primary myoblasts were characterized in assays of cell proliferation and differentiation. Primary myoblasts were dependent on added bFGF for growth and retained the ability to differentiate even after 30 population doublings. The fate of the pure myoblast populations after transplantation was monitored by labeling the cells with the marker enzyme beta-galactosidase (beta-gal) using retroviral mediated gene transfer. Within five days of transplantation into muscle of mature mice, primary myoblasts had fused with host muscle cells to form hybrid myofibers. To examine the immunobiology of primary myoblasts, we compared transplanted cells in syngeneic and allogeneic hosts. Even without immune suppression, the hybrid fibers persisted with continued beta-gal expression up to six months after myoblast transplantation in syngeneic hosts. In allogeneic hosts, the implanted cells were completely eliminated within three weeks. To assess tumorigenicity, primary myoblasts and myoblasts from the C2 myogenic cell line were transplanted into immunodeficient mice. Only C2 myoblasts formed tumors. The ease of isolation, growth, and transfection of primary mouse myoblasts under the conditions described here expand the opportunities to study muscle cell growth and differentiation using myoblasts from normal as well as mutant strains of mice. The properties of these cells after transplantation--the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity--suggest that studies of cell-mediated gene therapy using primary myoblasts can now be broadly applied to mouse models of human muscle and non-muscle diseases.