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PubMed2026

Low-Grade Myofibroblastic Sarcoma Represents an Epigenetically Distinct Myofibroblastic Tumor With USP6 Upregulation and Stable Genome.

Low-grade myofibroblastic sarcoma (LGMS) is a rare, indolent mesenchymal neoplasm exhibiting myofibroblastic differentiation, with a propensity for local recurrence. The molecular basis of LGMS and its precise relationship with other histological mimics have remained largely undefined. To address this gap, we conducted the first comprehensive multiomics analysis of 6 LGMS cases, integrating whole-exome sequencing, RNA sequencing, and Illumina Methylation EPICv2 array profiling with comparative analysis against public sarcoma methylation cohorts and related fibroblastic tumors. Clinically, patients (median age 35.5 years) presented with small tumors (median size 1.45 cm), predominantly located in the head and neck, displaying classic histological features of diffusely infiltrative spindle cell fascicles with patchy mononuclear inflammation. Two of the 5 patients with follow-up developed local recurrence, and none metastasized (median follow-up duration 92.5 months). Genomically, all LGMS exhibited a low tumor mutational burden (median 2.31 mut/Mb) and a minimal fraction of genome altered, with TP53 and TSC2 deletions and NTRK1 and ERBB3 amplifications found in a subset of cases. No pathogenic fusions were detected. Transcriptomic profiling revealed a distinct signature featuring prominent USP6 overexpression and upregulation of inflammatory and immune-related genes, including CD274 (PD-L1), and enrichment of inflammatory and interferon-gamma response signatures. Epigenetically, LGMS formed a unique methylation cluster closest to inflammatory myofibroblastic tumor, with numerous differentially methylated regions and higher immune infiltration, particularly monocytes, compared with other fibroblastic tumors. These findings establish LGMS as a genomically stable, epigenetically distinct myofibroblastic sarcoma driven by USP6 overexpression and an inflammation-enriched transcriptome. They support its recognition as a standalone entity, facilitate integration into methylation-based sarcoma classifiers for improved diagnostic precision, and nominate USP6-associated pathways and immune checkpoint blockade as promising therapeutic strategies for recurrent or unresectable disease.

Humans↗

PubMed1979

Inhibition of myofibroblasts by skin grafts.

The myofibroblast population was studied by electron microscopy in rat wounds healing by (1) contraction of granulation tissue, (2) by coverage with split-skin grafts, and (3) by coverage with full-thickness skin grafts. In all 3 types of wounds, myofibroblasts appeared early and reached a peak number at two weeks after wounding. At this time, 40 to 50 percent of the wound fibroblasts had myofibroblast characteristics. The granulating wounds contracted rapidly and completely, and had long persistence of myofibroblasts. Split-skin grafted wounds contracted less and had a more rapid decrease in myofibroblasts. The wounds covered with full thickness skin grafts had a minimum of contraction with a very rapid decrease in the number of myofibroblasts until by 4 weeks no myofibroblasts were present. Full-thickness skin grafts thus appeared to influence contracting wounds not by preventing the formation of myofibroblasts, but by speeding up completion of their life cycle.

Animals↗

PubMed2026

TFPI-high myofibroblast states and a meta-program-related five-gene prognostic signature in breast cancer.

Intratumoral heterogeneity and tumor-microenvironment interactions limit prognostic stratification in breast cancer, but the prognostic relevance and cellular context of recurrent transcriptional meta-programs remain unclear. We aimed to derive a meta-program-related prognostic signature and characterize its component transcripts at single-cell resolution. Six paired institutional tumors and adjacent non-tumor tissues served as a proof-of-concept comparison. Univariable Cox screening and least absolute shrinkage and selection operator Cox regression were used to derive a five-gene score from a prespecified meta-program-related candidate set in The Cancer Genome Atlas Breast Invasive Carcinoma (TCGA-BRCA) training cohort; the score was tested internally and assessed in GSE20685 using fixed coefficients and cohort-specific median cutoffs. GSE161529 single-cell transcriptomic data were used to map signature transcripts across 136,526 quality-controlled cells, while donor-aware pseudobulk analysis compared upper- and lower-quartile TFPI expression states in annotated myofibroblasts. The score comprised TCN1, FOXJ1, PIGR, SLAIN1, and TFPI and was associated with overall survival in the training, testing, and external cohorts, with concordance indices of 0.782, 0.756, and 0.721, respectively. TFPI transcripts were detected across endothelial, fibroblast, and myofibroblast compartments. TFPI-high myofibroblasts showed transcriptional enrichment of extracellular matrix and collagen fibril organization, transforming growth factor beta signaling, epithelial-mesenchymal transition, and myogenesis, together with lower oxidative phosphorylation and fatty acid metabolism programs. In bulk TCGA-BRCA tissue, TFPI expression correlated positively with stromal (r = 0.48), immune (r = 0.25), and composite microenvironment scores (r = 0.40; all p < 0.001). These findings identify a hypothesis-generating five-gene bulk-tissue prognostic signature and an expression-associated TFPI-high myofibroblast state but do not establish a discrete lineage, the cellular source of bulk TFPI, a TFPI-dependent mechanism, or clinical utility. Independent prospective cohorts, spatial and protein-level validation, and functional perturbation studies are required.

Journal Article↗

PubMed1979

Myofibroblasts in human breast tumors: an ultrastructural study.

Myofibroblasts were observed in the stroma of breast tumors in all cases examined by electron microscopy; 1 intraductal papillomatosis, 1 papillary carcinoma and 7 infiltrating duct carcinomas. The tubule- or duct-like structure in the tumor tissue were frequently surrounded by myofibroblasts which corresponded to delimiting fibroblasts in the normal breast tissue. In infiltrating duct carcinomas without tubule-like structures, myofibroblasts occurred dispersely in the stroma and they might correspond to fibroblasts in normal connective tissue. A possible role of these myofibroblasts as mesenchymal cells activated in a tumorous condition was discussed.

Breast Neoplasms↗

PubMed1977

Myofibroblasts and related cells in malignant fibrous and fibrohistiocytic tumors.

Myofibroblasts were detected by electron microscopy in five of five cases of fibrosarcoma and in five of six cases of malignant fibrous histiocytoma. In some areas myofibroblasts constituted up to 75 per cent of the tumor cells. Most myofibroblasts contained only sheaves of myofilaments along the margins of the cells, but some cells contained larger bundles of myofilaments and very closely resembled smooth muscle cells. An additional related type of cell was seen in several cases; it was large and possessed abundant eosinophilic cytoplasm, resembling a rhabdomyoblast at the light microscopic level. By electron microscopy this type of cell was seen to contain plentiful rough endoplasmic reticulum and large aggregates of fine filaments with rare dense bodies. These findings suggest that fibrosarcomas and malignant fibrous histiocytomas contain cells showing a spectrum of differentiation from fibrocytic to myogenic and that at the ultrastructural level the distinction between fibroblast and smooth muscle tumors may be blurred.

Adolescent↗

PubMed2026

Obese adipocytes induce fibroblast-to-myofibroblast transition through TGF-β1 signaling: implications in asthma pathogenesis.

Obesity, a key risk factor for severe asthma, is associated with worsening symptoms and poor responses to conventional therapies. Recent studies have highlighted the presence of adipocytes within airway walls, which correlates positively with body mass index (BMI). However, the role of adipocytes in asthma pathogenesis remains largely unknown. This study aims to explore their potential contribution to airway fibrosis, a progressive form of the disease, through fibroblast-to-myofibroblast transition (FMT). In vitro coculture models were developed to investigate the interactions between adipocytes (derived from patients with and without obesity) and fibroblasts (from patients with and without asthma) on FMT. Proteomic and multiplex analyses were used to identify potential mediators of adipocyte-induced FMT. Our data revealed a significant increase in fibrogenic markers, such as alpha-smooth muscle actin and vimentin, in fibroblasts cocultured with obese (Ob) adipocytes. Notably, this transition was more pronounced in asthmatic fibroblasts compared with healthy fibroblasts. Proteomic profiling of cocultured Ob-adipocytes and asthmatic fibroblasts identified several significantly upregulated proteins linked to the regulation of the transforming growth factor-beta (TGF-β) signaling pathway, including inhibin A, latent TGF-β binding protein 1, thrombospondin 1, and follistatin. The role of TGF-β was further substantiated by multiplex assays, which demonstrated a significant increase in TGF-β and leptin production by Ob-adipocytes following coculture. These findings suggest that Ob-adipocytes may promote FMT in fibroblasts, especially asthmatic fibroblasts, by activating the TGF-β signaling pathway. This highlights a potential mechanism by which obesity exacerbates asthma severity and fibrosis, providing new avenues for therapeutic intervention.NEW & NOTEWORTHY Adipocytes have been found in the airway wall of patients with obesity. This study is the first to show that adipocytes derived from patients with obesity can induce features of airway remodeling that is seen in patients with asthma such as fibroblast-to-myofibroblast transition via the TGF-beta signaling pathway in an indirect mode of cellular communication. This highlights a potential mechanism by which obesity exacerbates asthma severity and fibrosis, providing new avenues for therapeutic intervention.

Humans↗

PubMed2026

Pediatric intracranial inflammatory myofibroblastic tumor harboring DCTN1::ALK fusion: a case report with radiologic-pathologic-molecular correlation.

Central nervous system inflammatory myofibroblastic tumors are rare; pediatric DCTN1::ALK fusion cases are exceptionally uncommon. Here, we present an eight-year-old boy who presented with headache, vomiting, and a rapidly enlarging right frontal scalp mass. An MRI showed a dural, extra-axial lesion with mass effect. Histology confirmed IMT, and ALK immunohistochemistry was positive; next-generation sequencing (NGS) identified DCTN1 (exon 1-27)-ALK (exon 20-29) fusion, and FISH confirmed ALK rearrangement (33/100 nuclei). Genomic metrics showed tumor mutational burden (TMB) of 0.94/Mb, microsatellite stability, and CNV burden of 2.1%. He underwent near total resection followed by alectinib; to our knowledge, this is the first reported young pediatric (<10 years old) CNS IMT with this fusion.

Humans↗

PubMed2026

Loss of Methylthioadenosine Phosphorylase (MTAP) Expression: A Potentially Useful Tool for Distinguishing Sarcomatoid Urothelial Carcinoma From Inflammatory Myofibroblastic Tumor.

Inflammatory myofibroblastic tumor (IMT) and sarcomatoid urothelial carcinoma (SarUC) can have striking histologic overlap but have significantly different prognoses and clinical management paradigms. Loss of methylthioadenosine phosphorylase (MTAP) protein expression by immunohistochemistry (IHC) serves as a useful surrogate for homozygous 9p21 deletion, a recurrent genomic alteration in urothelial carcinoma (UC). We analyzed MTAP expression by IHC in 65 SarUCs and 27 urinary tract IMTs to evaluate its utility in navigating this challenging differential diagnosis. Overall, MTAP loss was significantly more frequent in SarUC (55%) compared with IMT (4%) (P < .0001). Among 46 biphasic SarUCs with independently evaluable epithelial and mesenchymal components, divergent expression patterns were frequent. The most common pattern was retention of MTAP staining in both epithelial and mesenchymal components (19/46; 41% of cases), followed by selective retention of MTAP in the epithelial component and loss in the mesenchymal component (16/46; 35% of cases). MTAP loss was observed in both the epithelial and mesenchymal components in 11 out of 46 (24%) SarUC cases. None of the 46 biphasic SarUC cases showed selective MTAP loss in the epithelial component but retention in the mesenchymal component. MTAP IHC was also particularly valuable in assessing clonal relationships in 2 challenging biphasic cases in which the differential diagnosis included a collision between a noninvasive low-grade papillary UC and an IMT versus a subtle IMT-like SarUC arising in association with an overlying noninvasive low-grade papillary UC. Next-generation sequencing on a subset of cases (n = 11) was useful for confirming 9p deletion in cases with MTAP loss by IHC, and for demonstrating molecular hallmarks of urothelial neoplasia thereby providing additional diagnostic support for morphologically challenging SarUC cases with IMT-like morphology. Therefore, MTAP IHC can be useful in evaluating spindle cell lesions of the urinary tract, as loss is significantly more common in SarUC than in IMT, and enriched in the mesenchymal component of biphasic SarUC. However, MTAP loss can be seen in both entities, and the diagnosis of IMT-like spindle cell tumors in the urinary tract requires careful integration of morphologic, immunohistochemical, and molecular data.

Humans↗

PubMed2026

A systematic literature review on low-grade myofibroblastic sarcoma of the trunk.

BACKGROUND: Low-grade myofibroblastic sarcoma (LGMS) is a rare malignant mesenchymal tumor, with primary trunk involvement being particularly uncommon. Due to its rarity, associated diagnostic challenges, and variability in management, a comprehensive evaluation of the available evidence is required. This study aims to systematically review the clinical characteristics, treatment strategies, and outcomes of truncal LGMS. METHODS: A systematic literature search was conducted using PubMed, Web of Science, and Embase for articles published from January 1998 to January 2026. The review included full-text articles involving patients with a pathologically confirmed diagnosis of truncal LGMS. The collected data included patient demographics, tumor features, treatment modalities, recurrence, and follow-up status. RESULTS: Of the 404 studies initially identified, 30 studies involving 59 patients with pathologically confirmed truncal LGMS met the inclusion criteria. Outcome analyses of therapeutic management and clinical course included 45 patients with complete follow-up data, including 42 surgically treated patients and 3 non-surgically managed patients. The final evidence base consisted solely of retrospective studies and case reports. No prospective studies or randomized controlled trials were identified. Consequently, a descriptive statistical analysis was conducted instead of a meta-analysis. CONCLUSION: Current evidence indicates that wide excision with negative margins may be a reasonable primary treatment option for truncal LGMS, with case-based reports showing numerically lower recurrence after wide excision, although the evidence is limited and potentially confounded by multiple factors. Radiotherapy or chemotherapy may be considered only on a highly individualized basis for selected unresectable, recurrent, metastatic, anatomically constrained, or margin-positive cases. Given the very limited sample size and heterogeneous treatment indications across published cases, treatment efficacy cannot be reliably estimated from the available data. Prolonged long-term regular follow-up is recommended for all patients, considering the risk of late recurrence.

Humans↗

PubMed1979

Ultrastructural evidence of myofibroblasts in pseudomalignant myositis ossificans.

Seven cases of pseudomalignant ossifying myositis with a typical clinical symptomatology have been reported. None of the cases had experienced an injury. All the lesions were intramuscular and all of them showed a zonal arrangement. Electron microscopy in three cases allowed the demonstration of cells showing morphological features of myofibroblasts and monocytic cells of the macrophage type. These previously unreported features together with the zonal pattern of the lesions indicate their reparative nature.

Adolescent↗

PubMed1979

A myofibroblastic tumor. Infantile digital fibroma (recurrent digital fibrous tumor of childhood).

Infantile digital fibromas are distinctive tumors both clinically and morphologically. A unique light microscopic features in the presence of intracytoplasmic, spherical, eosinophilic inclusion bodies. Previous electron microscopic studies have shown these bodies to consist of fibrils; bundles of fibrils have also been described in the cytoplasm. We have examined one such tumor, confirmed earlier findings, and established that the component cells are typical myofibroblasts. The latter are a variety of fibroblasts first described in granulation tissue; they are endowed with contractile properties and are characterized ultrastructurally by bundles of fibrils containing "dense bodies" such as are found in smooth muscle cells. Since our case is identical to those previously described, we propose that this tumor be called infantile digital myofibroblastoma.

Basement Membrane↗

PubMed1979

Fibrin gel investment associated with line 1 and line 10 solid tumor growth, angiogenesis, and fibroplasia in guinea pigs. Role of cellular immunity, myofibroblasts, microvascular damage, and infarction in line 1 tumor regression.

Line 1 and line 10 tumors became invested in a fibrin-gel cocoon within hours after transplantation to the subcutaneous spaces of unsensitized syngeneic inbred Sewall Wright strain 2 guinea pigs. The fibrin gel comprised more than 80% of the line 1 tumor mass and, after day 3, became organized and was subsequently replaced by fibrous connective tissue, which gave the tumor the appearance of a scirrhous carcinoma. A cellular infiltrate of lymphocytes and basophils developed at the periphery of line 1 tumors after day 8, and tumors regressed by day 13. The fibrin gel investing the highly malignant line 10 tumors accounted for less than 10% of the tumor mass and persisted without fibrous organization as a tumor grew progressively and invaded adjacent tissues. These data provide new and potentially important insights into the biology of solid tumor growth and the mechanisms of immunologic tumor rejection. Envelopment of tumors in a fibrin gel created an anatomic barrier separating the tumors from the host. Neovascularization mimicking that about line 1 and line 10 tumors was induced by sc fibrin implants; these data suggest that activation of the clotting and/or fibrinolytic systems by tumor cells may itself provide sufficient stimulus for induction of tumor angiogenesis without requiring a separate tumor angiogenesis factor. The scirrhous pattern of growth characteristic of line 1 tumors apparently was achieved by organization of an abundant fibrin gel. Line 1 tumor regression did not for the most part involve direct contacts between tumor cells and any type of inflammatory cell, including macrophages; rather, tumor destruction was effected by ischemic necrosis secondary to widespread microvascular injury. The mechanisms of such injury are uncertain, but tumor rejection was correlated with evidence of developing cellular immunity and anatomic associations between lymphocytes and myofibroblasts. Further experiments will be necessary before these findings can be generalized to other tumor systems.

Animals↗

PubMed1977

[The myofibroblast. Recent advances (author's transl)].

The myofibroblast morphology is analyzed from the literature. The absence of the specific structural characters previously used for identification is emphasized and the physiological properties are analyzed. The different conditions which influence the appearance of this cell under normal and pathological conditions are reviewed and shown to be associated specially with inflammatory processes. As a conclusion, the evolution of the cell is described to the perspective of mesenchymal dynamics.

Fibroblasts↗

PubMed1979