Molecular characterization of inflammatory myofibroblastic tumors with frequent ALK and ROS1 gene fusions and rare novel RET rearrangement

Assessment of ALK Fusions in Uncommon Inflammatory Myofibroblastic Tumors With ALK IHC Positivity but FISH-Equivocal Findings by Targeted RNA Sequencing

CONTEXT.—

Fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) are common methods to detect ALK status in inflammatory myofibroblastic tumors (IMTs). However, equivocal ALK FISH signals and inconsistency between FISH and IHC are occasionally observed.

OBJECTIVE.—

To study the inconsistency between FISH and IHC, and clarify ALK status in IMT by targeted RNA sequencing (RNAseq).

DESIGN.—

In this study, 12 consultation cases preliminarily diagnosed as uncommon IMTs with ALK IHC positivity but FISH negativity, plus 3 ALK-positive and 3 ALK-negative IMTs, were re-analyzed by IHC, FISH, and RNAseq.

RESULTS.—

As a result, 1 case with FUS-TFCP2 fusion was detected by RNAseq, which was previously misdiagnosed as IMT. In the other 11 uncommon IMTs, 90.9% (10 of 11) showed equivocal ALK FISH signals, and all were confirmed to harbor ALK fusion by RNAseq, except for 1 failure, suggesting that a low threshold for ALK FISH might be proposed in IMT. Furthermore, RNAseq also identified IGFBP5-ALK in 1 case with ALK IHC positivity but typical FISH negativity, suggesting the possibility of false negatives for ALK FISH. For the typical IMTs, ALK fusion was identified by RNAseq in all 3 ALK-positive IMTs as expected, and additionally FN1-ROS1 fusions were identified in 2 of 3 ALK-negative IMTs.

CONCLUSIONS.—

These findings indicated that RNAseq can simultaneously detect multiple gene fusions and provide fusion forms and breakpoints, which is of great value for differential diagnosis, especially for those uncommon IMTs with equivocal FISH findings, or inconsistency between IHC and FISH.

Clinicopathologic and Genomic Characterization of Inflammatory Myofibroblastic Tumors of the Head and Neck: Highlighting a Novel Fusion and Potential Diagnostic Pitfall

Inflammatory myofibroblastic tumor (IMT) is a distinctive fibroblastic and myofibroblastic spindle cell neoplasm with an accompanying inflammatory cell infiltrate and frequent receptor tyrosine kinase activation at the molecular level. The tumor may recur and rarely metastasizes. IMT is rare in the head and neck region, and limited information is available about its clinicopathologic and molecular characteristics in these subsites. Therefore, we analyzed a cohort of head and neck IMTs through a multi-institutional approach. Fourteen cases were included in the provisional cohort, but 1 was excluded after molecular analysis prompted reclassification. Patients in the final cohort included 7 males and 6 females, with a mean age of 26.5 years. Tumors were located in the larynx (n=7), oral cavity (n=3), pharynx (n=2), and mastoid (n=1). Histologically, all tumors showed neoplastic spindle cells in storiform to fascicular patterns with associated chronic inflammation, but the morphologic spectrum was wide, as is characteristic of IMT in other sites. An underlying fusion gene event was identified in 92% (n=11/12) of cases and an additional case was ALK-positive by IHC but could not be evaluated molecularly. ALK represented the driver in all but 1 case. Rearrangement of ALK, fused with the TIMP3 gene (n=6) was most commonly detected, followed by 1 case each of the following fusion gene partnerships: TPM3-ALK, KIF5B-ALK, CARS-ALK, THBS1-ALK, and a novel alteration, SLC12A2-ROS1. The excluded case was reclassified as spindle cell rhabdomyosarcoma after detection of a FUS-TFCP2 rearrangement and retrospective immunohistochemical confirmation of rhabdomyoblastic differentiation, illustrating an important diagnostic pitfall. Two IMT patients received targeted therapy with crizotinib, with a demonstrated radiographic response. One tumor recurred but none metastasized. These results add to the growing body of evidence that kinase fusions can be identified in the majority of IMTs and that molecular analysis can lead to increased diagnostic accuracy and broadened therapeutic options for patients.

ALK rearrangements in infantile fibrosarcoma-like spindle cell tumours of soft tissue and kidney

AIMS

Recurrent alterations in receptor tyrosine kinase (RTK) and downstream effectors are described in infantile fibrosarcoma (IFS)/cellular congenital mesoblastic nephroma (cCMN) and a subset of spindle cell sarcomas, provisionally designated 'NTRK-rearranged' spindle cell neoplasms. These two groups of tumours demonstrate overlapping morphologies and harbour alterations in NTRK1/2/3, RET, MET, ABL1, ROS1, RAF1 and BRAF, although their relationship is not fully elucidated. We describe herein a cohort of paediatric tumours with clinicopathological features not typical for inflammatory myofibroblastic tumour, but rather with similarities to cCMN/IFS harbouring ALK fusions.

METHODS AND RESULTS

Clinicopathological features were assessed and partner agnostic targeted RNA sequencing on clinically validated platforms were performed. Tumours occurred in patients aged from 2 to 10 years (median age 2 years) with a 2:2 male to female ratio and an average size of 8.4 cm. Two tumours arose in soft tissues and two in the kidney. Morphological features included spindle to ovoid cells arranged in long fascicles or haphazardly within a myxoid to collagenised stroma; a subset of cases had either dilated, ectatic vessels or focal perivascular hyalinosis. By immunohistochemistry, all cases tested showed cytoplasmic expression of anaplastic lymphoma kinase (ALK) and one case demonstrated co-expression of CD34 and S100.

CONCLUSIONS

This series of ALK-rearranged IFS-like tumours expands the spectrum of targetable kinases altered in these tumours and reinforces the potential overlap between IFS/cCMN-like tumours and the provisional entity of 'NTRK-rearranged' spindle cell neoplasms.

NTRK-Rearranged soft tissue neoplasms: A review of evolving diagnostic entities and algorithmic detection methods

The spectrum of tumors with NTRK1/2/3 rearrangements has expanded with widespread use of next generation sequencing (NGS) technology. For many years it was known that a majority of infantile fibrosarcomas (IFS), and their counterpart in the kidney, cellular congenital mesoblastic nephroma, contain the recurrent ETV6-NTRK3 fusion. Sequencing RNA transcripts from IFS and their morphologically similar counterparts in older children and adults has shown rearrangements with other 5' partners combined with NTRK1, NTRK2, and NTRK3 can also occur. For those tumors occurring outside of the infant age group, this has resulted in a proposed new diagnostic entity of "NTRK-rearranged spindle cell neoplasm." The clinical behavior of NTRK rearranged soft tissue tumors varies, though most show localized disease with rare metastases. The pathology of NTRK rearranged tumors exists on a spectrum, with overlapping features of classic infantile fibrosarcoma, lipofibromatosis, and malignant peripheral nerve sheath tumor. In this tumor spectrum, clinical and pathologic predictive factors are largely still to be determined, with no clear association between histologic grade and severity of disease. Of critical importance is detection of the NTRK rearrangement in order to guide treatment in patients with unresectable and metastatic disease. While resection is the definitive treatment, these tumors do show response to targeted TRK kinase inhibitors. Multiple detection methods are available, including immunohistochemistry, FISH, and next generation sequencing, which each have their merits and potential pitfalls. We aim to review the clinical characteristics and histomorphology of mesenchymal tumors with NTRK rearrangements as well as discuss molecular detection methods and diagnostic algorithms specific for soft tissue tumors.

Inflammatory Myofibroblastic Tumor 12 Years After Treatment for Synovial Sarcoma: A Case Report

Inflammatory myofibroblastic tumors (IMTs) are mesenchymal neoplasms most seen in the abdominopelvic region, lung, and retroperitoneum; and less commonly seen in virtually any other site. We report a case of two lower limb masses consistent with diagnosis of IMTs. This is a 39-year-old woman with a history of right lower extremity popliteal fossa synovial sarcoma diagnosed 12 years prior and treated with chemotherapy, surgery, and radiation. She presented with two new - one anterior and one posterior - right thigh masses. Biopsies of the lesions demonstrated low-grade inflammatory spindle cell lesions at both sites. Wide resection was performed for both masses and further characterization of the surgical specimens was most consistent with IMT. At follow-up, the patient is well with no signs of recurrence 19 and 7 months postoperative to the resection of the anterior and posterior thigh masses, respectively. This case represents the first reported IMTs occurring as late as 12 years after primary cancer treatment, and the first occurring after synovial sarcoma.

Pancreatic Masses in Children and Young Adults: Multimodality Review with Pathologic Correlation

Masses and masslike lesions of the pancreas are uncommon in the pediatric population. However, owing to overlapping clinical and imaging features, it can be challenging to differentiate the various causes of pediatric pancreatic masses at initial patient presentation. Clinical data such as patient age, signs and symptoms at presentation, laboratory test results, and potential underlying cancer predisposition syndrome can be helpful when formulating a differential diagnosis. US may be the first imaging study to depict a pancreatic mass in a child, as this examination is frequently performed in children with nonspecific abdominal signs and symptoms because of its wide availability and relatively low cost and the lack of a need for sedation or anesthesia. CT or MRI is typically required for more thorough characterization of the mass and surgical planning. Complete characterization of pancreatic masses includes assessment of vascular involvement, local invasion, and extrapancreatic spread of tumor. The authors provide an up-to-date comprehensive review of the clinical manifestations, histopathologic features, and imaging findings of primary and secondary tumors of the pancreas in children and young adults. Advances in imaging, current prognostic information, and treatment paradigms also are highlighted. Finally, nontumorous masslike lesions of the pediatric pancreas, including vascular malformations, cystic disorders (eg, von Hippel-Lindau syndrome, cystic fibrosis), intrapancreatic accessory spleen, and autoimmune pancreatitis, are discussed. Online supplemental material is available for this article. ^©RSNA, 2021.

Comprehensive Molecular Analysis of Inflammatory Myofibroblastic Tumors Reveals Diverse Genomic Landscape and Potential Predictive Markers for Response to Crizotinib

PURPOSE

The European Organization for Research and Treatment of Cancer (EORTC) clinical phase II trial 90101 "CREATE" showed high antitumor activity of crizotinib, an inhibitor of anaplastic lymphoma kinase (ALK)/ROS1, in patients with advanced inflammatory myofibroblastic tumor (IMFT). However, recent findings suggested that other molecular targets in addition to ALK/ROS1 might also contribute to the sensitivity of this kinase inhibitor. We therefore performed an in-depth molecular characterization of archival IMFT tissue, collected from patients enrolled in this trial, with the aim to identify other molecular alterations that could play a role in the response to crizotinib.

EXPERIMENTAL DESIGN

Twenty-four archival IMFT samples were used for histopathological assessment and DNA/RNA evaluation to identify gene fusions, copy-number alterations (CNA), and mutations in the tumor tissue. Results were correlated with clinical parameters to assess a potential association between molecular findings and clinical outcomes.

RESULTS

We found 12 ALK fusions with 11 different partners in ALK-positive IMFT cases by Archer analysis whereas we did not identify any ROS1-rearranged tumor. One ALK-negative patient responding to crizotinib was found to have an ETV6-NTRK fusion in the tumor specimen. The CNA profile and mutational landscape of IMFT revealed extensive molecular heterogeneity. Loss of chromosome 19 (25% of cases) and PIK3CA mutations (9% of cases) were associated with shorter progression-free survival in patients receiving crizotinib.

CONCLUSIONS

We identified multiple genetic alterations in archival IMFT material and provide further insight into the molecular profile of this ultra-rare, heterogeneous malignancy, which may potentially translate into novel treatment approaches for this orphan disease.

Second Paediatric Strategy Forum for anaplastic lymphoma kinase (ALK) inhibition in paediatric malignancies: ACCELERATE in collaboration with the European Medicines Agency with the participation of the Food and Drug Administration

The first (2017) and sixth (2021) multistakeholder Paediatric Strategy Forums focused on anaplastic lymphoma kinase (ALK) inhibition in paediatric malignancies. ALK is an important oncogene and target in several paediatric tumours (anaplastic large cell lymphoma [ALCL], inflammatory myofibroblastic tumour [IMT], neuroblastoma and hemispheric gliomas in infants and young children) with unmet therapeutic needs. ALK tyrosine kinase inhibitors have been demonstrated to be active both in ALK fusion-kinase positive ALCL and IMT. ALK alterations differ, with fusions occurring in ALCL, IMT and gliomas, and activating mutations and amplification in neuroblastoma. While there are many ALK inhibitors in development, the number of children diagnosed with ALK driven malignancies is very small. The objectives of this ALK Forum were to (i) Describe current knowledge of ALK biology in childhood cancers; (ii) Provide an overview of the development of ALK inhibitors for children; (iii) Identify the unmet needs taking into account planned or current ongoing trials; (iv) Conclude how second/third-generation inhibitors could be evaluated and prioritised; (v) Identify lessons learnt from the experience with ALK inhibitors to accelerate the paediatric development of other anti-cancer targeted agents in the new regulatory environments. There has been progress over the last four years, with more trials of ALK inhibitors opened in paediatrics and more regulatory submissions. In January 2021, the US Food and Drug Administration approved crizotinib for the treatment of paediatric and young adult patients with relapsed or refractory ALCL and there are paediatric investigation plans (PIPs) for brigatinib and for crizotinib in ALCL and IMT. In ALCL, the current goal is to investigate the inclusion of ALK inhibitors in front-line therapy with the aim of decreasing toxicity with higher/similar efficacy compared to present first-line therapies. For IMT, the focus is to develop a joint prospective trial with one product in children, adolescents and adults, taking advantage of the common biology across the age spectrum. As approximately 50% of IMTs are ALK-positive, molecular analysis is required to identify patients to be treated with an ALK inhibitor. For neuroblastoma, crizotinib has not shown robust anti-tumour activity. A focused and sequential development of ALK inhibitors with very good central nervous system (CNS) penetration in CNS tumours with ALK fusions should be undertaken. The Forum reinforced the strong need for global academic collaboration, very early involvement of regulators with studies seeking possible registration and early academia-multicompany engagement. Innovations in study design and conduct and the use of 'real-world data' supporting development in these rare sub-groups of patients for whom randomised clinical trials are not feasible are important initiatives. A focused and sequenced development strategy, where one product is evaluated first with other products being assessed sequentially, is applicable for ALK inhibitors and other medicinal products in children.

Uterine mesenchymal tumors harboring ALK fusions and response to ALK-targeted therapy

Inflammatory myofibroblastic tumor (IMT) of the uterus is a rare but aggressive malignancy that is often misdiagnosed. Approximately 50% of uterine IMTs (UMT) harbor rearrangements involving the ALK gene on chromosome 2p23 with subsequent overexpression of the ALK protein. Molecular characterization and wider availability of immunohistochemistry (IHC) and next generation sequencing (NGS) have improved clinical recognition and accurate diagnosis of UMT. The discovery of ALK fusions as a genomic driver led to the FDA approval of ALK inhibitors in ALK-altered lung cancers, but there are limited data to date on the spectrum of ALK fusions or patterns of response and resistance to ALK inhibitors in ALK-altered UMT. In this report we describe the genomic and histopathological characteristics and the response to ALK-targeted therapy in four patients with UMT. In all four patients, clinical activity of ALK inhibition was observed, with durable responses lasting 12 months or more. Moreover, three patients derived benefit from a second-generation ALK inhibitor after progression of disease or intolerance to the first-generation inhibitor crizotinib. Our report advocates for consideration of expanding the current National Comprehensive Cancer Network (NCCN) guidelines to include later-generation ALK inhibitors for the treatment of ALK-rearranged UMTs.

First report of an adult female patient with endobronchial inflammatory myofibroblastic tumor in Taiwan: A case report

An inflammatory myofibroblastic tumor (IMT) of the respiratory system is an uncommon disease. In Taiwan, there is a lack of previous studies on tracheobronchial IMT. The tumor is characterized by overexpression of anaplastic lymphoma receptor tyrosine kinase (ALK)‐1. Surgical resection is the standard treatment of choice nowadays.

Molecular Alterations in Pediatric Fibroblastic/Myofibroblastic Tumors: An Appraisal of a Next Generation Sequencing Assay in a Retrospective Single Centre Study

BACKGROUND

Pediatric fibroblastic/myofibroblastic tumors (PFMTs) can be challenging to definitively classify. Large case series or diagnostic updates have not been recently published despite identification of molecular alterations that could improve diagnostic accuracy. Our review of the literature found that over two-thirds of the more than 30 types of PFMTs harbor recurrent molecular alterations. We performed an institutional review of PFMTs to highlight limitations of a predominantly morphological classification, and evaluated the utility of a next-generation sequencing assay to aid diagnosis.

METHODS

PFMTs identified over a period of 12 years were reviewed, categorized per the new WHO classification, and tested using the Oncomine Childhood Cancer Research Assay.

RESULTS

Eighty-seven specimens from 58 patients were reviewed; 50 were chosen for molecular analysis, 16 (32%) lacking definitive classification. We identified alterations, some novel, in 33% of assayed cases. Expected alterations were identified for most known diagnoses and mutations were identified in 6 of 16 tumors (38%) that were initially unclassified.

CONCLUSION

We confirmed a significant subset of PFMTs remain difficult to classify using current criteria, and that a combined DNA/RNA assay can identify alterations in many of these cases, improving diagnostic certainty and suggesting a clinical utility for challenging cases.

Mesenchymal Tumors of the Mediastinum: An Update on Diagnostic Approach

Mesenchymal tumors of the mediastinum are a heterogenous group of rare tumors with divergent lineages. Mediastinal mesenchymal tumors are diagnostically challenging due to their diversity and morphologic overlap with nonmesenchymal lesions arising in the mediastinum. Accurate histologic diagnosis is critical for appropriate patient management and prognostication. Many mediastinal mesenchymal tumors affect distinct age groups or occur at specific mediastinal compartments. Neurogenic tumors, liposarcoma, solitary fibrous tumor, and synovial sarcoma are common mesenchymal tumors in the mediastinum. Herein, we provide an update on the diagnostic approach to mediastinal mesenchymal tumors and a review of the histologic features and differential diagnosis of common benign and malignant mesenchymal tumors of the mediastinum.

Gastric mesenchymal tumor with smooth muscle differentiation and echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion

Gastric mesenchymal tumors are relatively rare, and their molecular pathogeneses are poorly understood, except for gastrointestinal stromal tumor, desmoid, and inflammatory myofibroblastic tumors. We report a case of a gastric mesenchymal tumor with prominent smooth muscle cell differentiation and an echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion. On gross section, the tumor was 26 mm at the largest diameter, well-circumscribed, and located in the submucosal and muscular layers of the stomach wall. Histologically, the tumor comprised intersecting fascicles of spindle cells, non-atypical nuclei, and highly eosinophilic cytoplasm. Myxoid changes were observed focally, but inflammatory infiltrates were only evident in limited areas. Immunochemical staining revealed that the tumor was positive for α-smooth muscle actin and desmin. Diffuse positive staining for h-caldesmon was observed throughout the tumor, which suggested smooth muscle cell differentiation. Intracytoplasmic staining for ALK protein was also observed, and fluorescence in situ hybridization using ALK break-apart probes showed split chromosomal signals. RNA-sequencing analysis identified EML4-ALK fusion transcripts. We concluded that the tumor was a gastric mesenchymal tumor with smooth muscle differentiation based on its distinct differential smooth muscle properties, such as highly eosinophilic cytoplasm and diffuse expression of h-caldesmon. Furthermore, activated ALK may underly the tumor's pathogenesis.

Cardiac fibroma: A clinicopathologic study of a series of 12 cases

BACKGROUND

Cardiac fibroma (CF) is a rare tumor that has not been widely reported. This study investigated the clinical findings, histologic features, and differential diagnosis of CF.

METHODS

A total of 12 CF cases were studied and reviewed using hematoxylin and eosin (H&E), special staining and immunohistochemical staining. The ALK gene was tested in 4 cases of cardiac fibroma with significant inflammatory cells. Clinicopathological data were retrospectively analyzed and followed up.

RESULTS

The cases occurred in six males and six females ranging in age from 0.5 to 55 years (median, 5 years). The tumors were grossly single and solid (1-17 cm; mean 5.6 cm). The clinical signs and symptoms depended largely on the location of the tumor. Microscopically, the CFs observed were composed of monomorphic spindle cells and abundant collagen. The spindle cells demonstrated little or no atypia. The histology of CFs in infants and young children showed some differences from those in adults. Infants and young children with fibromas exhibited cellular types with more inflammatory infiltration. All tumors expressed vimentin markers. Eleven of 12 cases (91.7%) were positive for SMA by immunohistochemistry. ALK immunostaining and ALK-FISH tests showed negative results. Follow-up information was available for all patients. The mean postoperative follow-up was at 3 years (range 2 months-8.8 years). All patients were alive with no evidence of disease.

CONCLUSIONS

Our study shows that CFs exhibit a wide morphological spectrum of soft tissue tumors with fibroblastic or myofibroblastic differentiation and/or components. Infants and younger pediatric patients with fibromas have tumors that are more hypercellular and more likely to be misdiagnosed with aggressive or malignant lesions than adults. Finally, the data indicate that CF exhibits benign behavior and that local resection is safe and effective.

MUC4 Expression in Angiomatoid Fibrous Histiocytoma

Angiomatoid fibrous histiocytoma (AFH) is a rarely metastasizing neoplasm that typically occurs in the deep dermis and subcutis of the extremities of young patients, characterized by a t(2;22) translocation involving EWSR1 and CREB1. Because of its distinctive histologic features, the diagnosis of AFH is generally straightforward, although the immunohistochemistry (IHC) findings are relatively nonspecific. We recently encountered a case of primary cranial AFH that showed strong MUC4 IHC expression, which has not yet been reported previously. Prompted by this surprising finding, we investigated MUC4 expression in a series of AFH to evaluate this potential diagnostic pitfall. The expression of ALK by IHC, recently discovered in AFH, was also assessed in this study. We also analyzed EWSR1 rearrangement by fluorescence in situ hybridization using a dual color break-apart probe to confirm the diagnosis. The results showed MUC4 expression in 22.2% of AFH cases (4/18 cases), demonstrating a variable intensity of cytoplasmic staining. Most notably, one of the positive cases showed strong and diffuse expression. ALK IHC expression was observed in 17 of 18 cases (94.4%), usually in a diffuse and strong cytoplasmic pattern. EWSR1 rearrangement was demonstrated by fluorescence in situ hybridization in 81.2% of cases (13 of 16), including all the MUC4-positive cases. Our results indicate that although the significance of MUC4 expression in AFH is unknown, it is important to be aware that a subset of AFH can express the protein by IHC, expanding a variety of MUC4-positive mesenchymal tumors.

Clinical Utility of Anchored Multiplex Solid Fusion Assay for Diagnosis of Bone and Soft Tissue Tumors

Sarcoma diagnosis has become increasingly complex, requiring a combination of morphology, immunohistochemistry, and molecular studies to derive specific diagnoses. We evaluated the role of anchored multiplex polymerase chain reaction-based gene fusion assay in sarcoma diagnostics. Between 2015 and 2018, bone and soft tissue sarcomas with fusion assay results were compared with the histologic diagnosis. Of 143 sarcomas tested for fusions, 43 (30%) had a detectable fusion. In review, they could be classified into 2 main categories: (1) 31 tumors with concordant morphologic and fusion data; and (2) 12 tumors where the fusion panel identified an unexpected rearrangement that played a significant role in classification. The overall concordance of the fusion assay results with morphology/immunohistochemistry or alternate confirmatory molecular studies was 83%. Collectively, anchored multiplex polymerase chain reaction-based solid fusion assay represents a robust means of detecting targeted fusions with known and novel partners. The predictive value of the panel is highest in tumors that show a monomorphic cell population, round cell tumors, as well as tumors rich in inflammatory cells. However, with an increased ability to discover fusions of uncertain significance, it remains essential to emphasize that the diagnosis of bone and soft tissue neoplasms requires the integration of morphology and immunohistochemical profile with these molecular methods, for accurate diagnosis and optimal clinical management of sarcomas.

Uterine inflammatory myofibroblastic tumor: First report of a ROS1 fusion

Inflammatory myofibroblastic tumor (IMT) of the uterus is an uncommon mesenchymal neoplasm that frequently harbors ALK rearrangements. In this report, we describe the first uterine IMT with a FN1-ROS1 fusion, which occurred in a 43-year-old woman who presented with menorrhagia. Morphologically, the well-circumscribed 3 cm tumor was comprised of compact and myxoid foci of relatively bland spindle cells admixed with scattered chronic inflammatory cells limited to the myxoid areas. ROS1 showed moderate cytoplasmic granular staining in < 30% of cells in the myxoid foci, while ALK was negative. RNA sequencing detected a FN1-ROS1 rearrangement that fused FN1 exon 37 to ROS1 exon 34. Although non-ALK-rearranged uterine IMTs are exceedingly rare, this example highlights the importance of performing ROS1 immunohistochemistry and/or molecular analysis in ALK-negative uterine neoplasms morphologically compatible with IMT.

Rapid Response to Lorlatinib in a Patient With TFG-ROS1 Fusion Positive Inflammatory Myofibroblastic Tumor of the Chest Wall Metastatic to the Brain and Refractory to First and Second Generation ROS1 Inhibitors

Most inflammatory myofibroblastic tumors (IMTs) harbor ALK fusions but oncogene fusions involving ROS1, RET, NTRK, and PDGFR also occur. The recognition that most IMTs harbor receptor tyrosine kinase fusions has provided a rationale for the use of tyrosine kinase inhibitors to target these oncogenic drivers in advanced IMTs. Crizotinib has been effective in ALK and ROS1-positive IMTs but resistance eventually develops. Here we report the successful use of lorlatinib in a patient with heavily pretreated ROS1-positive IMT of the chest wall with acquired crizotinib-resistance and metastasis to the brain.

Inflammatory myofibroblastic tumor: molecular landscape, targeted therapeutics, and remaining challenges

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal tumor of intermediate malignant potential that predominantly affects children, adolescents and young adults. IMT has a predilection for the lung, abdomen, pelvis, and retroperitoneum, however, can affect any part of the body. IMT is typically localized, and multifocal or metastatic disease is uncommon. Complete surgical resection is the treatment of choice when feasible. There is no established standard of care for unresectable and advanced IMT. Approximately half of IMTs harbor anaplastic lymphoma kinase (ALK) gene rearrangements, and fusions involving ROS1, PDGFRβ, RET and NTRK have also been described. Given the molecular landscape of IMT, management of these tumors has evolved to include tyrosine kinase inhibitors and novel targeted therapeutics. This review highlights the molecular characteristics, evolution of targeted therapies and the remaining challenges in the management of IMT.

Uterine Inflammatory Myofibroblastic Neoplasms With Aggressive Behavior, Including an Epithelioid Inflammatory Myofibroblastic Sarcoma: A Clinicopathologic Study of 9 Cases

The experience with uterine inflammatory myofibroblastic neoplasms with an unfavorable outcome is limited. We present the clinicopathologic features of 9 such cases, including 8 inflammatory myofibroblastic tumors (IMTs) and 1 epithelioid inflammatory myofibroblastic sarcoma (EIMS). Median patient age for the IMT group was 50.5 years; the patient with EIMS was 43 years old. Patients presented with abnormal uterine bleeding, presumed fibroids, pelvic pain, arthralgia and low-grade fever, as well as an incidental finding. Median tumor size for the IMTs was 8.5 cm. The borders were either infiltrative or well-circumscribed. Histologically, IMTs were purely fascicular or myxoid or showed predominance of one or the other pattern. Seven tumors were spindled, and 1 was both spindled and epithelioid. Tumors had variable nuclear atypia, ranging from grade 1 to 3. All tumors had an inflammatory infiltrate-predominantly lymphocytic, majority had necrosis (62.5%) and none had lymphovascular invasion. 7/8 (87.5%) tumors were positive for ALK-1 by immunohistochemistry (IHC). One tumor was negative for ALK-1 by IHC but was positive for ALK fusion by fluorescence in situ hybridization and had TNS1-ALK fusion by next-generation sequencing (NGS). Three other tumors with NGS testing showed one of the following ALK-fusion partners: FN1, DCTN1, and IGFBP5. The EIMS had infiltrative borders, myxoid and hyalinized patterns, epithelioid cells, and no lymphovascular invasion. This tumor was ALK-1 positive by IHC, had ALK rearrangement by fluorescence in situ hybridization and RANBP2-ALK fusion by NGS. Extrauterine disease at time of diagnosis was noted in 2/8 (25%) of IMTs, and in the single case of EIMS. Seven patients had surgery as primary treatment, 1 patient had neoadjuvant chemotherapy and 1 patient declined treatment. Patients with recurrence were treated with a combination of chemotherapy, targeted therapy, radiotherapy or hormonal therapy. Most patients (71.4%) recurred within 24 months (mos). Two thirds of patients were alive with disease at last follow up (mean 43.6 mos). The patient with EIMS was alive with disease at 22 mos. IMT referral cases were initially diagnosed as smooth muscle tumors in 87.5% of cases; while the EIMS was diagnosed as high-grade endometrial stromal sarcoma. Lack of consideration of IMT in the differential diagnosis of smooth muscle tumors with myxoid features can result in misdiagnosis and under-utilization of targeted therapy in these patients.

Therapeutic options in inoperable ROS1-rearranged inflammatory myofibroblastic tumor of the tongue in a child: a case report and literature review

Inflammatory myofibroblastic tumor (IMT) is a rare borderline malignancy, usually treated with surgery only. Exceedingly rare cases of inoperable, recurrent, or metastatic IMTs pose a therapeutic challenge. We report successful treatment of a 7-year-old girl with an inoperable anaplastic lymphoma kinase (ALK)-negative IMT of the tongue. The patient underwent various anti-inflammatory (steroids, nonsteroidal anti-inflammatory drugs, clarithromycin) and antiproliferative (chemotherapy) therapies to enable tumor regression and complete resection. Ultimately, next-generation sequencing of the tumor revealed a TFG-ROS-1 translocation, allowing for an off-label targeted therapy with crizotinib. Crizotinib treatment caused slight tumor regression but evident change of its structure, allowing for complete non-mutilating resection. Two histopathology examinations revealed complete disappearance of neoplastic cells following therapy. The patient remains disease-free 22 months after the delayed surgery. In children with inoperable ALK-negative IMTs, molecular testing must be performed to identify other targetable oncogenic fusions, including TFG-ROS1.

Inflammatory Myofibroblastic Tumor of the Upper Airways Harboring a New TRAF3-ALK Fusion Transcript

Inflammatory myofibroblastic tumor (IMT) is a rare disease that mainly involves the lung and the abdomen with an intermediate clinical course but a recurrence rate between 15–30%. Radical surgery represents the gold standard of treatment, while chemotherapy and radiotherapy are considered for unresectable lesions. The identification of ALK translocations in IMT opened the option for the use of target therapies. Indeed, the ALK inhibitors have changed the treatment approach for aggressive lesions, improving the prognosis. Intraluminal upper-way IMT is extremely rare and represents a medical challenge. We reported an endotracheal IMT case presenting a previously unknown TRAF3-ALK fusion transcript.

Outstanding Response in a Patient With ROS1-Rearranged Inflammatory Myofibroblastic Tumor of Soft Tissues Treated With Crizotinib: Case Report

Inflammatory myofibroblastic tumor (IMT) is a very rare subtype of sarcoma, which frequently harbor chromosomal rearrangements, including anaplastic lymphoma kinase (ALK) rearrangements (almost 50% of the IMTs) and other kinase fusions such as ROS1. ROS1 fusions are present in about 10% of IMT, almost half of the ALK-negative IMT patients. Apart from radical surgery for resectable tumors, there is no standard-of-care therapy for advanced IMTs. Nonetheless, the use of tyrosine kinase inhibitors has shown promising efficacy in IMT patients with targetable genomic alterations. We report the case of a 24-year-old patient with chemotherapy-refractory metastatic IMT harboring ROS1 kinase fusion, who experienced a significant clinical and pathological response to crizotinib. This clinical case highlights the need to assess all patients with unresectable IMTs for chromosomal abnormalities and gene mutations and address them to targeted agents as well as clinical trials.

Mesenchymal tumours of the gastrointestinal tract

Mesenchymal tumours represent a heterogenous group of neoplasms encopassing benign, intermediate malignancy, and malignant entities. Sarcomas account for approximately 1% of human malignancies. In consideration of their rarity as well as of intrinsic complexity, diagnostic accuracy represents a major challenge. Traditionally, mesenchymal tumours are regarded as lesions the occurrence of which is mostly limited to somatic soft tissues. However, the occurrence of soft tissue tumours at visceral sites represent a well recognized event, and the GI-tract ranks among the most frequently involved visceral location. There exist entities such as gastrointestinal stromal tumours (GIST) and malignant gastointestinal neuroectodermal tumors that exhibit exquisite tropism for the GI-tract. This review will focus also on other relevant clinico-pathologic entities in which occurrence at visceral location is not at all negligible.

Durable response to serial tyrosine kinase inhibitors (TKIs) in an adolescent with metastatic TFG-ROS1 fusion positive Inflammatory Myofibroblastic Tumor (IMT)

Here, we present the case of an adolescent with a rare metastatic Inflammatory myofibroblastic tumor (IMT) harboring a TFG-ROS1 fusion initially detected on tumor progression and retrospectively identified in the primary tumor after targeted RNA sequencing. The patient benefitted from sequential TKIs over a 5-year period with response to the third generation ALK/ROS inhibitor, lorlatinib leading to resection of the primary tumor. Detailed molecular analysis can identify targetable oncogenic kinase fusions that alters management in patients with unresectable disease and should be considered in all patients.

ALK-negative lung inflammatory myofibroblastic tumor in a young adult: A case report and literature review of molecular alterations

RATIONALE

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal tumor that is prevalent among children and adolescents. Surgery is the most important therapeutic approach for IMT and complete resection is recommended. Although 50% of IMTs show anaplastic lymphoma kinase (ALK) rearrangements, crizotinib has proven an effective therapeutic approach. However, the genetic landscape of this tumor is still not fully understood and treatment options are limited, especially in the majority of ALK-negative tumors.

PATIENT CONCERNS

We describe the clinical case of a healthy 18-year-old female in whom a pulmonary nodule was incidentally detected.

DIAGNOSES

Following a small increase in the size of the nodule, the patient underwent both 18FDG-PET/CT and 68Ga-PET/CT, resulting in a suspicion of bronchial hamartoma.

INTERVENTIONS

The patient underwent surgery and a salivary gland-like lung tumor was diagnosed.

OUTCOMES

After surgery, the patient was referred to our cancer center, where a review of the histology slides gave a final diagnosis of ALK-negative lung IMT. Given the histology, it was decided not to administer adjuvant therapy and the patient was placed in a 3-monthly follow-up program. The patient is still disease-free 2 years post-surgery.

LESSONS

Although there is no standard of care for the treatment of IMT, identifying genomic alterations could help to redefine the management of patients with negative-ALK disease. Our review of the literature on IMT and other kinase fusions revealed, in addition to ALK rearrangements, the potential association of ROS1, NTRK, RET, or PDGFR beta alterations with the tumor.

Case Report: Circulating Tumor Cells as a Response Biomarker in ALK-Positive Metastatic Inflammatory Myofibroblastic Tumor

Inflammatory myofibroblastic tumors (IMTs) are locally aggressive malignancies occurring at various sites. Surgery is the mainstay of treatment and prognosis is generally good. For children with unresectable or metastatic tumors, however, outcome is particularly severe, limited also by the lack of predictive biomarkers of therapy efficacy and disease progression. Blood represents a minimally invasive source of cancer biomarkers for real-time assessment of tumor growth, particularly when it involves the analysis of circulating tumor cells (CTC). As CTCs potentially represent disseminated disease, their detection in the blood correlates with the presence of metastatic lesions and may reflect tumor response to treatment. Herein, we present a case report of a 19-year-old boy with an ALK-positive IMT of the bladder, proximal osteolytic and multiple bilateral lung lesions, who received ALK inhibitor entrectinib postoperatively and underwent longitudinal CTC analysis during treatment. Antitumor activity of entrectinib was demonstrated and was accompanied by regression of lung lesions, elimination of CTCs from the blood and no development of relapses afterwards. Therapy continued without any clinical sign of progression and 24 months since the initiation of treatment the patient remains symptom-free and disease-free.

Curative, Organ-Sparing, Multimodal, Perioperative Treatment of a Young Patient with a Rectoanal Inflammatory Myofibroblastic Tumor

INTRODUCTION

We report the case of a young female patient with a technically resectable, nonmetastatic, rectoanal, anaplastic lymphoma kinase gene (ALK)-translocated inflammatory myofibroblastic tumor (IMFT).

CASE PRESENTATION

The patient was successfully treated preoperatively with the tyrosine kinase inhibitor (TKI) crizotinib, to downsize the primary tumor, followed by sphincter-sparing surgery, and adjuvant radiotherapy and crizotinib. She is now in follow-up with good sphincter function and with no evidence of active disease.

CONCLUSION

Pre- and postoperative treatment administration of crizotinib can be given with curative intent to patients with locally advanced, nonmetastatic IMFTs to avoid mutilating surgery.

Epstein-Barr Virus-Associated Smooth Muscle Tumors of Larynx: A Clinicopathologic Study and Comprehensive Literature Review of 12 Cases

Laryngeal mesenchymal neoplasms are rare, with smooth muscle tumors comprising a small subset. Specifically, Epstein-Barr virus (EBV)-associated smooth muscle tumors are exceptionally rare, lacking a comprehensive evaluation of their clinical and histologic features. Two patients (a 59 year old male and 51 year old female) had received renal transplants 156 and 240 months, respectively prior to onset of laryngeal symptoms. Supraglottic polypoid masses were identified and removed conservatively. Histologically, the tumors were hypercellular, showing alternating light and dark areas, the latter composed of primitive appearing round cells, while a more characteristic spindled tumor cell population was noted in the remaining areas. Cytoplasmic vacuoles were noted adjacent to the nucleus. There was no tumor necrosis or pleomorphism, but increased mitotic figures (11-12/2 mm²) were seen, without atypical forms. The tumor cells were strongly immunoreactive with smooth muscle actin and smooth muscle myosin heavy chain and with Epstein-Barr virus encoded RNA (EBER) by in situ hybridization. These patients were reviewed in the context of a thorough English literature review, which demonstrates a wide age range at presentation without a sex predilection, but with most patients from specific ethnic groups (Chinese, Thai, Pilipino). Three-quarters of patients are part of multifocal disease and the majority are post-renal transplantation patients. Conservative management seems to yield the best overall outcome for these indolent tumors. In conclusion, EBV-associated smooth muscle tumors should be considered in any immunocompromised patient with a head and neck smooth muscle tumor, especially when EBER is documented by in situ hybridization. Conservative management may be employed, even when multifocal tumors are documented.

Near-complete response to low-dose ceritinib in recurrent infantile inflammatory myofibroblastic tumour

Background

Infantile inflammatory myofibroblastic tumour (IMT) is rare and the majority are driven by anaplastic lymphoma kinase (ALK) rearrangements. Previous literature on the use of ALK inhibitors in paediatric IMTs is extremely limited with no published literature on the use in infants. Crizotinib and ceritinib are two ALK inhibitors which are available and have been used in IMTs; however, ceritinib is much more affordable in the low- and middle-income country (LMIC) setting than crizotinib.

Case

An 11-month-old child, who had undergone surgery for mesenteric IMT at the age of 3 months, had an unresectable recurrence with soft tissue deposits in the subdiaphragmatic location abutting the spleen and paravesical location. As surgery would have entailed splenectomy and partial cystectomy, she was treated with low-dose ceritinib (300 mg/m2/day) with which she had a near-complete response without any toxicity.

Discussion and conclusion

This is the first report of the use of ceritinib at a lower dose for infantile IMT having immense practical applications for the low- and middle-income setting.

Sustained complete response on crizotinib in primary lung inflammatory myofibroblastic tumor - Case report and literature review

Inflammatory myofibroblastic tumors (IMT) are rare soft tissue tumors of intermediate malignant potential occurring usually in children and adolescents. Treatment options for advanced diseases are limited. A 35-year-old lady presented to us with fever, cough and decreased appetite. On evaluation, she was diagnosed with left lung IMT. She underwent surgery and developed recurrence with pleural nodules after two years. Immunohistochemistry showed positivity for ALK (diffuse). Since recent evidence suggested that crizotinib is effective in advanced IMT with 50% response rates, she was treated with crizotinib 250mg BD with which she had a complete radiological response at three months. She has completed one year of treatment thus far and continues to be in complete remission. Treatment with ALK inhibitors like crizotinib has brought about a paradigm shift in the management of advanced ALK-positive IMT's with excellent clinical responses which are durable in a majority of cases.

JAK2 Rearrangements Are a Recurrent Alteration in CD30+ Systemic T-Cell Lymphomas With Anaplastic Morphology

Peripheral T-cell lymphoma (PTCL) comprises a heterogenous group of rare mature T-cell neoplasms. While some PTCL subtypes are well-characterized by histology, immunophenotype, and recurrent molecular alterations, others remain incompletely defined. In particular, the distinction between CD30+ PTCL, not otherwise specified and anaplastic lymphoma kinase (ALK)-negative anaplastic large cell lymphoma can be subject to disagreement. We describe a series of 6 JAK2 rearrangements occurring in a cohort of 97 CD30+ ALK- PTCL (6%), assembled after identifying an index case of a novel PABPC1-JAK2 fusion in a case of ALK- anaplastic large cell lymphoma with unusual classic Hodgkin lymphoma (CHL)-like features. Fusions were identified using a comprehensive next-generation sequencing based assay performed between 2013 and 2020. Five of 6 cases (83%) showed JAK2 rearrangements with 4 novel partners: TFG, PABPC1, ILF3, and MAP7, and 1 case demonstrated a previously described PCM1-JAK2 fusion. By morphology, all cases showed anaplastic large cells and multinucleated Reed-Sternberg-like cells within a polymorphous inflammatory background with frequent eosinophilia reminiscent of CHL. By immunohistochemistry, atypical large cells expressed CD30 with coexpression of at least 1 T-cell marker, aberrant loss of at least 1 T-cell marker and, in 4 of 5 cases stained (80%), unusual CD15 coexpression. These findings suggest that a subset of CD30+ ALK- systemic PTCL with anaplastic morphology carry JAK2 rearrangements, some of which appear to show CHL-like morphologic features. The presence of JAK2 rearrangements in cases of CD30+ PTCL augments current classification and may provide a therapeutic target via JAK2 inhibition.

The Most Common Mistake in Laryngeal Pathology and How to Avoid it

Upper aerodigestive tract (UADT) spindle cell squamous carcinoma (SCSC), also known as sarcomatoid carcinoma, is a high-grade subtype of conventional squamous cell carcinoma (SCC) that is histologically characterized by a combination of differentiated SCC in the form of intraepithelial dysplasia and/or invasive differentiated SCC, and the presence of an invasive (submucosal) undifferentiated malignant spindle-shaped and pleomorphic (epithelioid) cell component. Typically, SCSC presents as a superficial polypoid mass not infrequently with surface ulceration precluding identification of an intraepithelial dysplasia. Further, in many cases an invasive differentiated SCC is not identified. Adding to the complexity in such cases, is that immunohistochemical staining in a significant minority of cases is negative for epithelial-related markers but often the cells express mesenchymal-related markers. In such cases, differentiating SCSC from a reactive (benign) spindle cell proliferation or a mucosal-based sarcoma can be problematic, with treatment implications. Herein, we detail the clinical and pathologic features of laryngeal SCSC and discuss the rationale for diagnosing a carcinoma and avoiding a diagnosis of sarcoma. In our experience, such cases represent one of the more common mistakes made in laryngeal pathology. Yet, virtually all such lesions are SCSCs. The treatment and prognosis relies on the accuracy of this distinction.

[Diagnosis and therapy of tumors with NTRK gene fusion]

NTRK-Genfusionen sind seltene genetische Alterationen, die tumorentitätenübergreifend vorkommen können. Während sie in den meisten soliden Tumoren nur sehr niederfrequent vorkommen, lassen sie sich in bestimmten Tumoren wie dem infantilen Fibrosarkom, dem kongenitalen mesoblastischen Nephrom und dem sekretorischen Mamma- oder Speicheldrüsenkarzinom jedoch häufig nachweisen. NTRK-Genfusionen bzw. TRK-Fusionsproteine gelten als starke onkogene Treiber. Bei Nachweis von NTRK-Genfusionen können TRK-Inhibitoren unabhängig von der Tumorentität eingesetzt werden. Vertreter sind Entrectinib und Larotrectinib. Bislang ist nur Larotrectinib in der Europäischen Union zugelassen. Für beide wurden Wirksamkeit und Verträglichkeit in Phase-I- und Phase-II-Studien gezeigt. Die Seltenheit der TRK-Fusionstumoren stellt diagnostische und klinische Prozesse vor große Herausforderungen: Einerseits sollen alle Patienten mit TRK-Fusionstumoren identifiziert werden, andererseits sind epidemiologische und histologische Aspekte sowie Ressourcen zu berücksichtigen. Basierend auf diesen Punkten möchten wir einen Diagnosealgorithmus für TRK-Fusionstumoren vorschlagen, außerdem stellen wir aktuelle Daten zu den TRK-Inhibitoren vor.

Pseudosarcomatous myofibroblastic proliferations of the urinary bladder are neoplasms characterized by recurrent FN1-ALK fusions

Pseudosarcomatous myofibroblastic proliferation is a descriptive term that designates a group of clinically indolent genitourinary lesions that most commonly arise in the urinary bladder. Given that pseudosarcomatous myofibroblastic proliferation may show morphologic overlap with inflammatory myofibroblastic tumor, the relationship, if any, between the two entities has been unclear. Moreover, pseudosarcomatous myofibroblastic proliferations are known to be positive for ALK immunohistochemistry in a subset of cases, although an inconsistent association with ALK rearrangement (ranging from 0 to 60%) has been reported. The objectives of this study were to determine the frequency of ALK rearrangement and to identify fusion partners using fluorescence in situ hybridization (FISH) and targeted RNA sequencing studies in a contemporary series of 30 pseudosarcomatous myofibroblastic proliferations of the urinary bladder, as well as to investigate ROS1 status by immunohistochemistry. ALK immunohistochemistry was positive in 70% (21/30) of pseudosarcomatous myofibroblastic proliferations; ROS1 immunohistochemistry was consistently negative (0/28). ALK rearrangements were detected by FISH in 86% (18/21) of cases, correlating with ALK immunohistochemical positivity in all but 3 cases. Of eight cases confirmed to be ALK rearranged by FISH, targeted RNA-sequencing detected FN1-ALK fusions in seven (88%) cases, which involved exons 20-26 of FN1 (5') and exon 18-19 of ALK (3'). In conclusion, ALK rearrangements are frequent in pseudosarcomatous myofibroblastic proliferations, typically involving exon 19, and FN1 appears to be a consistent fusion partner. Given the significant clinicopathologic differences between inflammatory myofibroblastic tumor and pseudosarcomatous myofibroblastic proliferation, our findings provide further support for classification of pseudosarcomatous myofibroblastic proliferation as a distinct clinicopathologic entity, and propose the alternate terminology "pseudosarcomatous myofibroblastic neoplasm of the genitourinary tract."

An unusual case of a solitary cardiac myofibroma causing severe right ventricular outflow tract obstruction in an infant

Cardiac tumours are relatively uncommon, particularly in children. Myofibroma is an extremely rare variety of cardiac tumour, which nearly always arises in the context of infantile myofibromatosis. Herein, we present a case of a solitary cardiac myofibroma causing right ventricular outflow tract obstruction in a 2-month-old male infant.

A rare case of urachal inflammatory myofibroblastic tumor

Inflammatory myofibroblastic tumors (IMT) of the urachus is a rare neoplastic condition characterized by proliferation of spindle cell, likely derived from myofibroblasts or fibroblasts, with acute and chronic inflammatory infiltrate. Urachal IMT present with abdominal/pelvic pain and urinary symptoms. These often manifest as abdominal mass involving adjacent structures. We describe a case of young female with urachal IMT that was excised with a wide margin to ensure complete removal of all adjacent affected tissue using robotic-assisted laparoscopic approach. Immunohistochemical evidence of ALK and ALK gene rearrangement were confirmed in this tumor which are diagnostic of IMT.

Inflammatory Myofibroblastic Tumors in Children: A Clinical Retrospective Study on 19 Cases

Background: Inflammatory myofibroblastic tumor (IMFT) is a rare neoplasm mainly affecting children and young adults. We conducted a retrospective study to evaluate the clinical features and treatment alternatives of childhood inflammatory myofibroblastic tumors. Methods: A total of 19 patients who were pathologically diagnosed with IMT between December 2008 and October 2018 were included. Collected data were demographic information, main complaints, tumor characteristics, treatment, pathological results, immunohistochemical analysis, and prognosis. Results: The male/female ratio was 13:6. The mean age at disease onset was 44.9 ± 33.9 months (range 4 to 111 months). The mean tumor size was 6.5 ± 4.0 cm (range 1.2 to 17.0 cm). The most common site was the abdomen (13/19). The most commonly used detection tool was CT. Eleven patients (57.9%) had aggressive tumor growth, including eight receiving extensive resection and three receiving palliative resection due to high local invasiveness and postoperative chemotherapy. Eight cases whose tumors were completely enveloped received complete resection. Immunohistochemistry was performed for 17 patients and ALK positivity was found in 11 patients. Despite three children lost to follow-up, sixteen patients were followed up for 6 to 132 months (average 63.9 months, median 66 months). Of which, twelve children survived with no evidence of IMT, and four cases (21%) showed local recurrences (two of them died). No distant metastasis was detected. Conclusions: IMT is rare in children with various locations, mostly appearing in the abdomen. Whether the tumor could be completely removed, the location and the invasiveness of surrounding tissues might be highly prognosis-related.

ROS1-dependent cancers - biology, diagnostics and therapeutics

The proto-oncogene ROS1 encodes a receptor tyrosine kinase with an unknown physiological role in humans. Somatic chromosomal fusions involving ROS1 produce chimeric oncoproteins that drive a diverse range of cancers in adult and paediatric patients. ROS1-directed tyrosine kinase inhibitors (TKIs) are therapeutically active against these cancers, although only early-generation multikinase inhibitors have been granted regulatory approval, specifically for the treatment of ROS1 fusion-positive non-small-cell lung cancers; histology-agnostic approvals have yet to be granted. Intrinsic or extrinsic mechanisms of resistance to ROS1 TKIs can emerge in patients. Potential factors that influence resistance acquisition include the subcellular localization of the particular ROS1 oncoprotein and the TKI properties such as the preferential kinase conformation engaged and the spectrum of targets beyond ROS1. Importantly, the polyclonal nature of resistance remains underexplored. Higher-affinity next-generation ROS1 TKIs developed to have improved intracranial activity and to mitigate ROS1-intrinsic resistance mechanisms have demonstrated clinical efficacy in these regards, thus highlighting the utility of sequential ROS1 TKI therapy. Selective ROS1 inhibitors have yet to be developed, and thus the specific adverse effects of ROS1 inhibition cannot be deconvoluted from the toxicity profiles of the available multikinase inhibitors. Herein, we discuss the non-malignant and malignant biology of ROS1, the diagnostic challenges that ROS1 fusions present and the strategies to target ROS1 fusion proteins in both treatment-naive and acquired-resistance settings.

Inflammatory myofibroblastic tumour of the central airways: treatment and molecular analysis

Inflammatory myofibroblastic tumours (IMT) are a rare cause of endobronchial masses in adults. Surgery has been the mainstay of treatment of endobronchial IMTs, based on the potential for recurrence. Interventional pulmonology has emerged as a minimally invasive and lung function preserving modality in management of airway obstruction due to tumours. We present a series of three adult patients with IMT treated endobronchially with a short discussion on its potential role. We also discuss how molecular analysis of IMTs for mutations in genes such as ALK and ROS1 might provide insights into clinical behaviour and potential targetable therapy in advanced, unresectable and metastatic cases.

Spindle cell tumor with CD34 and S100 co-expression and distinctive stromal and perivascular hyalinization showing EML4-ALK fusion

Recently, a novel group of CD34+ and S100+ spindle cell tumors with distinctive stromal and perivascular hyalinization showing recurrent gene fusions involving RAF1, BRAF, NTRK1/2/3, and RET has been identified. ALK rearrangements have been rarely reported in this group of tumors. We report a 24-year-old woman with a 1.5-cm pink mass of the scalp. The tumor was made of spindle cells organized in fascicles or haphazardly arranged in a patternless architecture, with areas of stromal and perivascular hyalinization. The tumor cells diffusely expressed CD34 and S100, without SOX-10 expression. The tumor showed diffuse immunopositivity for ALK. RNA sequencing using next-generation sequencing (NGS) detected an EML4-ALK fusion. This case extends the spectrum of this newly described group of CD34+/S100+ spindle cell tumors at the molecular-genetic level. Dermatopathologists should be aware of this recent entity, as it may fall in the differential diagnosis of many other spindle cell tumors with CD34 expression. NGS-based techniques should be performed when facing spindle cell tumors with similar morphology and immunophenotype. Identification of kinase fusions is essential for the precise classification and better knowledge of these tumors, and for targeted therapy in rare aggressive cases.

Spitz Tumors With ROS1 Fusions: A Clinicopathological Study of 6 Cases, Including FISH for Chromosomal Copy Number Alterations and Mutation Analysis Using Next-Generation Sequencing

Spitz tumors represent a heterogeneous group of melanocytic neoplasms with a spectrum of biological behavior ranging from benign (Spitz nevus) to malignant (spitzoid melanoma). Prediction of the behavior of these lesions based on their histological presentation is not always possible. Recently, mutually exclusive activating kinase fusions, involving ALK, NTRK1, NTRK3, RET, MET, ROS1, and BRAF, have been found in a subset of spitzoid lesions. Some of these genetic alterations were associated with specific morphological features. Here, we report the histological presentation of 6 Spitz tumors with ROS1 fusion. The age of the patients ranged from 6 to 34 years, with strong female prevalence (5:1). All neoplasms were compound melanocytic proliferations with a predominant dermal growth but a conspicuous junctional component displaying atypical microscopic features qualifying them as atypical Spitz tumor. FIP1L1 and CAPRIN1 were identified as 2 novel 5'-fusion partners of ROS1 along with the known PWWP2A-ROS1 fusion. FISH for copy number changes of 9p21, 6p25, and 11q13 was negative in all but 1 neoplasm harboring isolated gain of 8q24. TERT-promoter hotspot mutation analysis was negative in all tumors. All patients are disease-free after a mean follow-up period of 30 months. It is concluded that ROS1-fused spitzoid neoplasms seem to have no distinctive histopathological features although consistent findings were spindled melanocytes arranged in confluent whorling nests, prominent transepidermal elimination of melanocytic nests, and myxoid/mucinous changes.