Congenital mesoblastic nephroma t(12;15) is associated with ETV6-NTRK3 gene fusion: cytogenetic and molecular relationship to congenital (infantile) fibrosarcoma

"Putting the cart before the horse": an update on promiscuous gene fusions in soft tissue tumors

The ever-increasing availability and affordability of molecular genetic testing has revolutionized our understanding of the pathogenesis and proper classification of soft tissue tumors but has also brought new challenges. As is known, many soft tissue tumors harbor gene fusion events, and while it was initially thought that individual entities would be defined by single, specific fusions, it quickly became clear that some entities could be caused by several different fusion events (e.g., EWSR1::FLI1, EWSR1::ERG, EWSR1:FEV and others in Ewing sarcoma). More recently, it has become apparent that these fusion events themselves are "promiscuous", appearing in more than one discrete entity (e.g., EWSR1::CREB1 in clear cell sarcoma, angiomatoid fibrous histiocytoma and others). This review article will briefly discuss the best known examples of genetic promiscuity, the EWSR1/FUS::ATF1/CREB1 and ETV6::NTRK3 fusions, and more comprehensively cover recently discovered and less well-known examples of genetic promiscuity, including EWSR1::WT1, MALAT1::GLI1, YAP1::TFE3 and fusions involving members of the FET and ETS gene families.

Application of RNA sequencing in urologic malignancies: Advances and challenges

RNA sequencing became a key tool in identifying the differences between cells and their functions, aiding in the recognition of the functional elements disrupted during the disease process. In urologic malignancies, many studies aiming to provide comprehensive molecular classifications through the assessment of RNA expression or fusion analysis have been published. The distinctive presence of these molecular alterations related to cancer development, growth, and survival and the discoveries of these breakthrough studies provide insight into the development of personalized management and aid in the identification of new therapeutic targets.

Pan-Cancer Molecular Biomarkers: Practical Considerations for the Surgical Pathologist

Traditional anatomic pathologic classification of cancer is based on tissue of origin and morphologic and immunohistochemical characterization of the malignant cells. With the technological improvements of massively parallel or next-generation sequencing, oncogenic drivers that are shared across different tumor types are increasingly being identified and used as pan-cancer biomarkers. This approach is reflected in the growing list of Food and Drug Administration-approved tumor-agnostic therapies, including pembrolizumab in the setting of microsatellite instability and high tumor mutational burden, larotrectinib and entrectinib for solid tumors with NTRK fusions, and combined dabrafenib-trametinib for BRAF V600E-mutated neoplasms. Several other biomarkers are currently under investigation, including fibroblast growth factor receptor (FGFR), RET, and ROS1 fusions; ERBB2 amplification; and mutations in the AKT1/2/3, NF1, RAS pathway and (mitogen-activated protein kinase (MAPK) pathway. As molecular assays are increasingly incorporated into routine tumor workup, the emergence of additional pan-cancer biomarkers is likely to be a matter more of "when" than "if." In this review, we first explore some of the conceptual and technical considerations at the intersection of surgical and molecular pathology, followed by a brief overview of both established and emerging molecular pan-cancer biomarkers and their diagnostic and clinical applications.

Mesenchymal Neoplasms of the Kidney and Perinephric Soft Tissue

Mesenchymal neoplasms of the kidney present challenges because they are uncommon, and because perinephric soft tissue biopsies are sometimes submitted as "kidney" masses, causing diagnostic confusion. Here, the author thoroughly reviews mesenchymal neoplasms of the kidney, including metanephric stromal tumor, classic and cellular congenital mesoblastic nephroma, anaplastic sarcoma and clear cell sarcoma of the kidney, malignant rhabdoid tumor, PEComa/angiomyolipoma, and anastomosing hemangioma. The author also discusses perinephric myxoid pseudotumor of fat, as well as diagnostic pitfalls presented by well-differentiated/dedifferentiated liposarcoma and sarcomatoid carcinoma.

Adjunctive diagnostic tool for histopathological classification of congenital mesoblastic nephroma based in molecular genetic findings

PURPOSE

Congenital mesoblastic nephromas (CMN) are histologically classified into classical, cellular, and mixed subtypes. Most cellular CMNs harbor ETV6-NTRK3 gene fusions, and classic and mixed CMNs harbor EGFR internal tandem duplications (EGFR-ITDs). Classic CMNs are considered benign, whereas recurrent or metastatic diseases occur in the cellular subtypes. Direct identification of mutations is desirable for an accurate diagnosis. However, molecular genetic analyses cannot be performed in a number of histopathology laboratories. This study aimed to investigate a surrogate marker for the accurate histological classification of CMN.

METHODS

Overall, 11 CMN cases diagnosed at our institute were included in this study. Reverse transcription-polymerase chain reaction was performed for the NTRK gene fusion and EGFR-ITDs in all cases. Comprehensive mRNA analysis was performed using the nCounter® Gene Expression Assay. Principal component analysis (PCA) was performed based on the gene expression levels. Immunohistochemical evaluation was conducted for the expression of p-Mek1/2, p-Erk1/2, and EGFR.

RESULTS

PCA revealed differences in mutation patterns between the EGFR-ITDs and NTRK fusion tumor groups. Gene ontology analysis of the highly expressed genes in the EGFR-ITDs tumor group revealed enrichment related to the mitogen-activated protein kinase (MAPK) signaling pathway. p-Mek1/2 and p-Erk1/2 immunoreactivity was significantly increased in the EGFR-ITDs tumor group (p = 0.018 and p = 0.017, respectively). EGFR immunoreactivity is not a useful marker for CMN with EGFR-ITD.

CONCLUSION

p-Mek1/2 and p-Erk1/2 immunoreactivity may be useful markers for EGFR-ITDs. Thus, MEK1/2 inhibitors possess the potential to be used as a targeted therapy for CMN with EGFR-ITDs.

Congenital Peribronchial Myofibroblastic Tumors Harbor a Recurrent EGFR Kinase Domain Duplication

Congenital peribronchial myofibroblastic tumor (CPMT) is a rare benign infantile pulmonary neoplasm that presents prenatally, or early in infancy, and exhibits distinctive histologic features characterized by the presence of cartilaginous islands intermixed with bland spindle cells, not uncommonly displaying prominent mitoses. Despite its benign nature, CPMT can lead to fetal demise, postnatal respiratory distress, or complications from perinatal surgical resection. Although the morphologic and clinical features of CPMT are well described, its molecular features and oncogenesis remain elusive. Following the detection of EGFR kinase domain duplication (KDD) of exons 18 to 25 in an index case, we identified 3 additional cases of morphologically classic and clinically well-characterized CPMTs from the archives and performed targeted RNA- and DNA-based profiling via next-generation sequencing for detection of rearrangements, sequence variants, and copy number variants on all cases. Two cases were detected prenatally, 1 patient presented at birth, and 1 at 8 weeks of life. All tumors were resected, with a follow-up period ranging from 0 days to 10 years. One patient died shortly after surgical resection, and the other 3 had no recurrences. In all cases, EGFR KDD was detected. In 2 out of 4 cases, gains of select whole chromosomes were noted. Our findings establish EGFR KDD as a recurrent oncogenic driver of CPMT. Notably, this alteration is also found in classical congenital mesoblastic nephromas, infantile kidney tumors with which CPMTs share striking morphologic and clinical similarities. This strongly suggests that CPMTs and classical congenital mesoblastic nephromas share common oncogenesis, and represent the same tumor in different locations. EGFR KDDs have also been reported in neonatal soft tissue tumors with infantile fibrosarcoma-like histology and cartilaginous differentiation, raising questions about their relationship. EGFR KDD emerges as a diagnostic marker, a potential therapeutic target, and a window into the oncogenesis of a distinct subset of infantile mesenchymal tumors.

Hallmark discoveries in the biology of non-Wilms tumour childhood kidney cancers

Approximately 20% of paediatric and adolescent/young adult patients with renal tumours are diagnosed with non-Wilms tumour, a broad heterogeneous group of tumours that includes clear-cell sarcoma of the kidney, congenital mesoblastic nephroma, malignant rhabdoid tumour of the kidney, renal-cell carcinoma, renal medullary carcinoma and other rare histologies. The differential diagnosis of these tumours dates back many decades, when these pathologies were identified initially through clinicopathological observation of entities with outcomes that diverged from Wilms tumour, corroborated with immunohistochemistry and molecular cytogenetics and, subsequently, through next-generation sequencing. These advances enabled near-definitive recognition of different tumours and risk stratification of patients. In parallel, the generation of new renal-tumour models of some of these pathologies including cell lines, organoids, xenografts and genetically engineered mouse models improved our understanding of the development of these tumours and have facilitated the identification of new therapeutic targets. Despite these many achievements, paediatric and adolescent/young adult patients continue to die from such rare cancers at higher rates than patients with Wilms tumour. Thus, international coordinated efforts are needed to answer unresolved questions and improve outcomes.

Update on cutaneous mesenchymal tumors in the 5th edition of WHO classification of skin tumors with an emphasis on new fusion-associated neoplasms

The section on mesenchymal tumors in the 5th edition of WHO classification of skin tumors has undergone several changes, the most important of which is the inclusion of newly identified tumor entities, which will be the main focus of this review article. These specifically include three novel cutaneous mesenchymal tumors with melanocytic differentiation, and rearrangements of the CRTC1::TRIM11, ACTIN::MITF, and MITF::CREM genes as well as EWSR1::SMAD3-rearranged fibroblastic tumors, superficial CD34-positive fibroblastic tumors, and NTRK-rearranged spindle cell neoplasms. Some of the other most important changes will be briefly mentioned as well.

A Novel Oncogenic and Drug-Sensitive KIF5B-NTRK1 Fusion in Lung Adenocarcinoma

We present a case of a lung adenocarcinoma patient harboring a novel kinesin family member 5B (KIF5B)-NTRK1 gene fusion that responds well to entrectinib. Moreover, KIF5B-NTRK1 gene chimera has been shown to be an oncogene, activating both the MAPK and PI3K/AKT signaling pathways. The biopsy sample was analyzed using various methods such as hematoxylin-eosin staining (HE), immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and next-generation sequencing (NGS) based on a 1267-gene panel. Additionally, human lung adenocarcinoma cell lines A549 and H1755 were used to obtain a stable expression of chimera gene products. The cell proliferation was confirmed using CCK8 and adhesion-dependent colony formation assay. Cell invasion was confirmed using the transwell invasion assay. The protein levels of the MAPK and PI3K/AKT signaling pathways were assessed using Western blotting. The patient, a 66-year-old Chinese male, was diagnosed with adenocarcinoma (stage IVB) located in the upper lobe of the left lung. NGS analysis identified a novel KIF5B-NTRK1 fusion gene, which was further confirmed by FISH and IHC analyses. As a first-line therapy, entrectinib was administered to the patient at a dose of 600 mg once daily, resulting in a partial response. The patient's progression-free survival (PFS) has now been more than 12 months, and no serious toxicities have been observed so far. Furthermore, stable KIF5B-NTRK1-expressing cells were generated and the experimental results demonstrate enhanced proliferation abilities, along with increased levels of proteins involved in the MAPK and PI3K/AKT signaling pathways. Our study reports a novel KIF5B-NTRK1 genetic rearrangement that supports favorable responses to entrectinib. Moreover, in vitro experiments showed that the fusion gene could exert oncogenic properties by activating the MAPK and PI3K/AKT signaling pathways. To summarize, our findings broaden the spectrum of NTRK gene fusions in the context of lung adenocarcinoma.

Pediatric Fibromatosis Lacks the Internal Tandem Duplication of EGFR Seen in Congenital Mesoblastic Nephroma

Classical and mixed congenital mesoblastic nephroma (CMN) are characterized by an internal tandem duplication (ITD) of the EGFR gene, in contrast to cellular CMN that usually harbors an ETV6::NTRK3 gene fusion. This same fusion occurs in infantile fibrosarcoma, and this tumor can be considered as the soft tissue equivalent of cellular CMN. A soft tissue equivalent of classic/mixed CMN remains undefined at the genetic level. Since classical CMN resembles fibromatosis of soft tissue histologically, we asked whether fibromatosis in children might show EGFR ITD. ITD was investigated using the polymerase chain reaction and primers for exons 18 and 25 of the EGFR gene. Seven of the eight cases of classical or mixed CMN were positive by this approach, but none of the five cellular CMNs. Of 11 cases of fibromatosis (six plantar, two digital, and three desmoid), none were positive for EGFR ITD. Within the limits of this small study, we conclude that pediatric fibromatosis is likely not characterized by EGFR ITD. There are isolated reports of pediatric soft tissue tumors that harbor EGFR ITD, but these have the appearance of infantile fibrosarcoma or mixed CMN rather than fibromatosis. We did not find any such cases, since all 14 cases of infantile fibrosarcoma in our study had an ETV6::NTRK3 fusion. The soft tissue tumors with EGFR ITD are not a morphologic match for the low-grade histology of classical CMN. Whether they have a similar favorable biology or behave more like fibrosarcoma with an ETV6::NTRK3 fusion or an alternative fusion involving other kinases remains to be determined.

Poor outcome in congenital mesoblastic nephroma with TPM3::NTRK1 fusion: a case report from multi-disciplinary treatment to molecular tumor board

Background

Congenital mesoblastic nephroma (CMN) is a rare renal tumor with good prognosis in children; however, cellular CMN is a special subtype with poor prognosis. The ETV6 fusion gene has been found in some cellular CMNs, whereas CMNs with TPM3::NTRK1 fusion gene have not been reported. This study aims to share the progression and treatment of a case of CMNs with TPM3::NTRK1 fusion gene, in order to provide experience for the diagnosis and treatment of such specific diseases.

Case Description

We report a case of CMN with TPM3::NTRK1 fusion gene and a 3-year course of disease that originated during the fetal period. The child experienced rapid tumor progression 22 months after birth, followed by tumor recurrence 3 months after complete resection of CMN. Although traditional chemotherapy could not prevent the tumor progression. The tropomyosin receptor kinase (TRK) inhibitor larotrectinib resulted in significant inhibitory effects on metastatic lesions in the lungs, liver, and peritoneum. However, the patient ultimately died as the tumor became resistant to larotrectinib.

Conclusions

CMN, is a rare pediatric renal tumor that warrant prompt surgical management. A watchful waiting approach may allow for aggressive growth of metastatic disease, as seen in this case of cellular CMN with TPM3::NTRK1 fusion gene, TRK inhibitors can play significant roles in the treatment of CMN with TPM3::NTRK1 fusion gene, but we still need to pay attention to the phenomenon of drug resistance to larotrectinib caused by site mutations of TRKA.

Back to the future! Selected bone and soft tissue neoplasms with shared genetic alterations but differing morphological and immunohistochemical phenotypes

Bone and soft tissue tumors (BST) are a highly heterogeneous group largely classified by their line of differentiation, based on their resemblance to their normal counterpart in adult tissue. Yet, rendering a specific diagnosis can be challenging, primarily due to their rarity and overlapping histopathologic features or clinical presentations. Over the past few decades, seemingly histogenetic-specific gene fusions/translocations and amplifications have been discovered, aiding in a more nuanced classification, leading to well-established objective diagnostic criteria and the development of specific surrogate ancillary tests targeting these genetic aberrations (e.g., immunohistochemistry). Ironically, the same research also has revealed that some specific tumor subtypes may be the result of differing and often multiple gene fusions/translocations, but, more interestingly, identical gene fusions may be present in more than one phenotypically and biologically distinct neoplasm, sometimes with entirely different clinical behavior. Prime examples include, EWSR1::ATF1 and, less commonly, EWSR1::CREB1 gene fusions present in both clear cell sarcoma, a malignant high-grade tumor with melanocytic differentiation, and angiomatoid fibrous histiocytoma, a mesenchymal neoplasm of intermediate malignancy with a generally indolent course. Similarly, MDM2 amplification, once deemed to be pathognomonic for atypical lipomatous tumor/well differentiated and dedifferentiated liposarcoma, has been documented in a range of additional distinct tumors, including low grade osteosarcomas (e.g. low grade central and surface parosteal) and high-grade intimal sarcomas, amongst others. Such findings reinforce the importance of careful attention to morphological and clinicoradiological features and correlation with molecular testing before rendering a specific diagnosis. Future classification systems in BST neoplasms cannot be solely based on molecular events and ideally will balance morphologic features with molecular analysis. Herein, we provide a narrative literature review of the more common BST neoplasms with shared genetic events but differing demographics, morphology, immunophenotype, and clinical behavior, re-emphasizing the importance of the hematoxylin and eosin slide and the "eye" of the practicing pathologist.

Comprehensive clinicopathological, molecular, and methylation analysis of mesenchymal tumors with NTRK and other kinase gene aberrations

Alterations in kinase genes such as NTRK1/2/3, RET, and BRAF underlie infantile fibrosarcoma (IFS), the emerging entity 'NTRK-rearranged spindle cell neoplasms' included in the latest WHO classification, and a growing set of tumors with overlapping clinical and pathological features. In this study, we conducted a comprehensive clinicopathological and molecular analysis of 22 cases of IFS and other kinase gene-altered spindle cell neoplasms affecting both pediatric and adult patients. Follow-up periods for 16 patients ranged in length from 10 to 130 months (mean 38 months). Six patients were treated with targeted therapy, achieving a partial or complete response in five cases. Overall, three cases recurred and one metastasized. Eight patients were free of disease, five were alive with disease, and two patients died. All cases showed previously reported morphological patterns. Based on the cellularity and level of atypia, cases were divided into three morphological grade groups. S100 protein and CD34 were at least focally positive in 12/22 and 14/22 cases, respectively. Novel PWWP2A::RET, NUMA1::RET, ITSN1::RAF1, and CAPZA2::MET fusions, which we report herein in mesenchymal tumors for the first time, were detected by RNA sequencing. Additionally, the first uterine case with BRAF and EGFR mutations and CD34 and S100 co-expression is described. DNA sequencing performed in 13 cases uncovered very rare additional genetic aberrations. The CNV profiles showed that high-grade tumors demonstrate a significantly higher percentage of copy number gains and losses across the genome compared with low- and intermediate-grade tumors. Unsupervised clustering of the tumors' methylation profiles revealed that in 8/9 cases, the methylation profiles clustered with the IFS methylation class, irrespective of their clinicopathological or molecular features. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

ETV6::NTRK3 Fusion-Positive Wild-Type Gastrointestinal Stromal Tumor (GIST) with Abundant Lymphoid Infiltration (TILs and Tertiary Lymphoid Structures): A Report on a New Case with Therapeutic Implications and a Literature Review

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, with proto-oncogene, receptor tyrosine kinase (c-kit), or PDGFRα mutations detected in around 85% of cases. GISTs without c-kit or platelet-derived growth factor receptor alpha (PDGFRα) mutations are considered wild-type (WT), and their diverse molecular alterations and biological behaviors remain uncertain. They are usually not sensitive to tyrosine kinase inhibitors (TKIs). Recently, some molecular alterations, including neurotrophic tyrosine receptor kinase (NTRK) fusions, have been reported in very few cases of WT GISTs. This novel finding opens the window for the use of tropomyosin receptor kinase (TRK) inhibitor therapy in these subtypes of GIST. Herein, we report a new case of NTRK-fused WT high-risk GIST in a female patient with a large pelvic mass (large dimension of 20 cm). The tumor was removed, and the histopathology displayed spindle-predominant morphology with focal epithelioid areas, myxoid stromal tissue, and notable lymphoid infiltration with tertiary lymphoid structures. Ten mitoses were quantified in 50 high-power fields without nuclear pleomorphism. DOG1 showed strong and diffuse positivity, and CD117 showed moderate positivity. Succinate dehydrogenase subunit B (SDHB) was retained, Pan-TRK was focal positive (nuclear pattern), and the proliferation index Ki-67 was 7%. Next-generation sequencing (NGS) detected an ETV6::NTRK3 fusion, and this finding was confirmed by fluorescence in situ hybridization (FISH), which showed NTRK3 rearrangement. In addition, an RB1 mutation was found by NGS. The follow-up CT scan revealed peritoneal nodules suggestive of peritoneal dissemination, and Entrectinib (a TRK inhibitor) was administered. After 3 months of follow-up, a new CT scan showed a complete response. Based on our results and the cases from the literature, GISTs with NTRK fusions are very uncommon so far; hence, further screening studies, including more WT GIST cases, may increase the possibility of finding additional cases. The present case may offer new insights into the potential introduction of TRK inhibitors as treatments for GISTs with NTRK fusions. Additionally, the presence of abundant lymphoid infiltration in the present case may prompt further research into immunotherapy as a possible additional therapeutic option.

Successful Crizotinib-targeted Therapy of Pediatric Unresectable ERC1::ALK Fusion Sarcoma

Anaplastic lymphoma kinase ( ALK )-fusion sarcomas are rare part of the emerging theoretically targetable tyrosine kinase RAS::MAPK pathway fusion myopericytic-ovoid sarcomas. We report our clinicopathologic and treatment experience with an ALK fusion sarcoma. A novel ELKS/RAB6-interacting/CAST family member 1 - unaligned ALK fusion infiltrative nonmetastatic low-grade sarcoma of the right hand of a 15-month-old male was treated with crizotinib, an ALK tyrosine kinase inhibitor as oral monotherapy, inducing complete radiographic and clinical resolution by 10 months and sustained response now over 12 months after elective discontinuation. Crizotinib can successfully be used to treat unresectable novel ALK fusion sarcomas.

The Diverse Roles of ETV6 Alterations in B-Lymphoblastic Leukemia and Other Hematopoietic Cancers

Genetic alterations of the repressive ETS family transcription factor gene ETV6 are recurrent in several categories of hematopoietic malignancy, including subsets of B-cell and T-cell acute lymphoblastic leukemias (B-ALL and T-ALL), myeloid neoplasms, and mature B-cell lymphomas. ETV6 is essential for adult hematopoietic stem cells (HSCs), contributes to specific functions of some mature immune cells, and plays a key role in thrombopoiesis as demonstrated by familial ETV6 mutations associated with thrombocytopenia and predisposition to hematopoietic cancers, particularly B-ALL. ETV6 appears to have a tumor suppressor role in several hematopoietic lineages, as demonstrated by recurrent somatic loss-of-function (LoF) and putative dominant-negative alterations in leukemias and lymphomas. ETV6 rearrangements contribute to recurrent fusion oncogenes such as the B-ALL-associated transcription factor (TF) fusions ETV6::RUNX1 and PAX5::ETV6, rare drivers such as ETV6::NCOA6, and a spectrum of tyrosine kinase gene fusions encoding hyperactive signaling proteins that self-associate via the ETV6 N-terminal pointed domain. Another subset of recurrent rearrangements involving the ETV6 gene locus appear to function primarily to drive overexpression of the partner gene. This review surveys what is known about the biochemical and genome regulatory properties of ETV6 as well as our current understanding of how alterations in these functions contribute to hematopoietic and nonhematopoietic cancers.

Phase separation underlies signaling activation of oncogenic NTRK fusions

NTRK (neurotrophic tyrosine receptor kinase) gene fusions that encode chimeric proteins exhibiting constitutive activity of tropomyosin receptor kinases (TRK), are oncogenic drivers in multiple cancer types. However, the underlying mechanisms in oncogenesis that involve various N-terminal fusion partners of NTRK fusions remain elusive. Here, we show that NTRK fusion proteins form liquid-like condensates driven by their N-terminal fusion partners. The kinase reactions are accelerated in these condensates where the complexes for downstream signaling activation are also concentrated. Our work demonstrates that the phase separation driven by NTRK fusions is not only critical for TRK activation, but the condensates formed through phase separation serve as organizational hubs for oncogenic signaling.

Report and follow-up on two new patients with congenital mesoblastic nephroma

BACKGROUND

Tumors are rare in neonatal age. Congenital mesoblastic nephroma (CMN) is a usually benign renal tumor observed at birth, or in the first months of life. It may also be identified prenatally and associated with polyhydramnios leading to preterm delivery. Effective treatment is surgical in most cases, consisting in total nephrectomy. In literature, very few studies report on the neonatal management of such a rare disease, and even less are those describing its uncommon complications.

CASES PRESENTATION

We report on two single-center newborns affected with CMN. The first patient is a preterm female baby, born at 30+ 1 weeks of gestation (WG) due to premature labor, with prenatal (25 WG) identification of an intra-abdominal fetal mass associated with polyhydramnios. Once obtained the clinical stability, weight gain, instrumental (computed tomography, CT, showing a 4.8 × 3.3 cm left renal neoformation) and histological/molecular characterization of the lesion (renal needle biopsy picture of classic CMN with ETV6-NTRK3 translocation), a left nephrectomy was performed at 5 weeks of chronological age. The following clinical course was complicated by intestinal obstruction due to bowel adherences formation, then by an enterocutaneous fistula, requiring multiple surgical approaches including transitory ileo- and colostomy, before the conclusive anastomoses intervention. The second patient is a 17-day-old male term baby, coming to our observation due to postnatal evidence of palpable left abdominal mass (soon defined through CT, showing a 7.5 × 6.5 cm neoformation in the left renal lodge), feeding difficulties and poor weight gain. An intravenous diuretic treatment was needed due to the developed hypertension and hypercalcemia, which regressed after the nephrectomy (histological diagnosis of cellular CMN with ETV6-NTRK3 fusion) performed at day 26. In neither case was chemotherapy added. Both patients have been included in multidisciplinary follow-up, they presently show regular growth and neuromotor development, normal renal function and no local/systemic recurrences or other gastrointestinal/urinary disorders.

CONCLUSIONS

The finding of a fetal abdominal mass should prompt suspicion of CMN, especially if it is associated with polyhydramnios; it should also alert obstetricians and neonatologists to the risk of preterm delivery. Although being a usually benign condition, CMN may be associated with neonatal systemic-metabolic or postoperative complications. High-level surgical expertise, careful neonatological intensive care and histopathological/cytogenetic-molecular definition are the cornerstones for the optimal management of patients. This should also include an individualized follow-up, oriented to the early detection of any possible recurrences or associated anomalies and to a better quality of life of children and their families.

Andrographis paniculata methanol extract suppresses the phosphorylation of ETV6‑NTRK3

ETS variant transcription factor 6 (ETV6)-neurotrophic receptor tyrosine kinase 3 (NTRK3) (EN) fusions are typically found in rare diseases, such as primary renal fibrosarcoma (only six cases have been reported), secretory carcinoma of the breast and salivary gland (1 case), and AML (4 cases). Few cases have been reported, and expression of the EN gene fusion requires additional clinical data and fundamental research to be supported. The aim of the present study was to determine the inhibitory effect of Andrographis paniculata methanol extract (MeAP) on EN-related cell lines, IMS-M2 and BaF3/EN, as well as evaluate the mechanism of action. Vero cells were used as control cells. Trypan blue staining and MTT were used to evaluate the inhibitory effect of MeAP on tested cells. Western blotting and immunoprecipitation were used to detect the activation of EN after MeAP treatment. The IC₅₀ values of MeAP were found to be 12.38±0.57 µg/ml (IMS-M2) and 13.06±0.49 µg/ml (BaF3/EN). MeAP was observed to inhibit cell proliferation in a time, dose, and cell density-dependent manner. The IC₅₀ value for MeAP in Vero cells was markedly higher, at 109.97±4.24 (µg/ml), indicating a much less sensitive effect. Furthermore, MeAP treatment inhibited EN phosphorylation and induced apoptosis in these cells. Collectively, the present study demonstrated that MeAP has an oncogenic effect on EN fusion-positive cell lines, in particular.

A challenging diagnosis of mammary analogue secretory carcinoma (MASC) on fine needle aspiration cytology and cell block: A cytopathologist's perspective

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland carcinoma that resembles the secretory carcinoma of the breast and is characterised by t(12;15) (q13;q25) translocation, which results in an ETV6-NTRK3 gene fusion product. On cytomorphology, it is characterised by papillary fragments, clusters, and singly dispersed tumour cells. These tumour cells are large and have abundant vacuolated cytoplasm. Acinic cell carcinoma of the salivary gland is the most common differential diagnosis of MASC. Other differentials include mucoepidermoid carcinoma, salivary duct carcinoma, pleomorphic adenoma, and oncocytic salivary gland neoplasms. Immunohistochemistry and morphology are critical in establishing the correct diagnosis. We present a case of a 46-year-old male patient diagnosed as MASC of the parotid gland on fine needle aspiration cytology and cell block.

NTRK Gene Fusions in Non-Small-Cell Lung Cancer: Real-World Screening Data of 1068 Unselected Patients

(1) Background: The main objectives of our study are (i) to determine the prevalence of NTRK (neurotrophic tyrosine kinase) fusions in a routine diagnostic setting in NSCLC (non-small cell lung cancer) and (ii) to investigate the feasibility of screening approaches including immunohistochemistry (IHC) as a first-line test accompanied by fluorescence in situ hybridization (FISH) and RNA-(ribonucleic acid-)based next-generation sequencing (RNA-NGS). (2) Methods: A total of 1068 unselected consecutive patients with NSCLC were screened in two scenarios, either with initial IHC followed by RNA-NGS (n = 973) or direct FISH testing (n = 95). (3) Results: One hundred and thirty-three patients (14.8%) were IHC positive; consecutive RNA-NGS testing revealed two patients (0.2%) with NTRK fusions (NTRK1-EPS15 (epidermal growth factor receptor pathway substrate 15) and NTRK1-SQSTM1 (sequestosome 1)). Positive RNA-NGS was confirmed by FISH, and NTRK-positive patients benefited from targeted treatment. All patients with direct FISH testing were negative. RNA-NGS- or FISH-positive results were mutually exclusive with alterations in EGFR (epidermal growth factor receptor), ALK (anaplastic lymphoma kinase), ROS1 (ROS proto-oncogene 1), BRAF (proto-oncogene B-Raf), RET (rearranged during transfection) or KRAS (kirsten rat sarcoma viral oncogene). Excluding patients with one of these alterations raised the prevalence of NTRK-fusion positivity among panTrk-(tropomyosin receptor kinase-) IHC positive samples to 30.5%. (4) Conclusions: NTRK fusion-positive lung cancers are exceedingly rare and account for less than 1% of patients in unselected all-comer populations. Both RNA-NGS and FISH are suitable to determine clinically relevant NTRK fusions in a real-world setting. We suggest including panTrk-IHC in a diagnostic workflow followed by RNA-NGS. Excluding patients with concurrent molecular alterations to EGFR/ALK/ROS1/BRAF/RET or KRAS might narrow the target population.

Japanese Society of Medical Oncology/Japan Society of Clinical Oncology/Japanese Society of Pediatric Hematology/Oncology-led clinical recommendations on the diagnosis and use of tropomyosin receptor kinase inhibitors in adult and pediatric patients with neurotrophic receptor tyrosine kinase fusion-positive advanced solid tumors

BACKGROUND

Clinical trials have reported the efficacy of tropomyosin receptor kinase (TRK) inhibitors against neurotrophic receptor tyrosine kinase (NTRK) fusion gene-positive advanced solid tumors. The accumulated evidence of tumor-agnostic agent has made since TRK inhibitors were approved and used in clinical practice. Therefore, we have revised the 'Japan Society of Clinical Oncology (JSCO)/Japanese Society of Medical Oncology (JSMO)-led clinical recommendations on the diagnosis and use of tropomyosin receptor kinase inhibitors in adult and pediatric patients with neurotrophic receptor tyrosine kinase fusion-positive advanced solid tumors, cooperated by the Japanese Society of Pediatric Hematology/Oncology (JSPHO)'.

METHODS

Clinical questions regarding medical care were formulated for patients with NTRK fusion-positive advanced solid tumors. Relevant publications were searched by PubMed and Cochrane Database. Critical publications and conference reports were added manually. Systematic reviews were performed for each clinical question for the purpose of developing clinical recommendations. The committee members identified by JSCO, JSMO, and JSPHO voted to determine the level of each recommendation considering the strength of evidence, expected risks and benefits to patients, and other related factors. Thereafter, a peer review by experts nominated from JSCO, JSMO, and JSPHO, and the public comments among all societies' members was done.

RESULTS

The current guideline describes 3 clinical questions and 14 recommendations for whom, when, and how NTRK fusion should be tested, and what is recommended for patients with NTRK fusion-positive advanced solid tumors.

CONCLUSION

The committee proposed 14 recommendations for performing NTRK testing properly to select patients who are likely to benefit from TRK inhibitors.

A Parotid Gland Mammary Analogue Secretory Carcinoma in a 4-Year-Old Boy: Case Report and Literature Review

Background: Mammary analogue secretory carcinoma (MASC) is characterized by similar histologic, immunohistochemical, and molecular features with breast secretory carcinoma. MASC usually occurs in adults. Case report: A 4-year-old boy presented with a right infra-auricular mass. Features of the tumor include solid, tubular, and papillary growth patterns, with homogenous eosinophilic secretions inside microcystic structures. Immunohistochemical stains showed strong, diffuse staining for CK7, S100, pan-TRK protein. P63 was positive in a peripheral pattern. Fluorescence in situ hybridization (FISH) analysis showed the characteristic ETV6-NTRK3 gene fusion. Conclusion: Typical histological, immunohistochemical, and molecular features are present in MASC occurring early in childhood.

Head and Neck Mesenchymal Tumors with Kinase Fusions: A Report of 15 Cases With Emphasis on Wide Anatomic Distribution and Diverse Histologic Appearance

Mesenchymal tumors harboring various kinase fusions were recently recognized as emerging entities mainly in the soft tissues. We herein investigate the clinicopathologic and molecular characteristics of head and neck mesenchymal tumors harboring kinase fusions. The study cohort included 15 patients with a median age of 13 years (ranging from congenital to 63 y). The kinase genes involved in descending order were NTRK1 (n=6), NTRK3 (n=5), BRAF (n=2), and 1 each with MET, and RET. The anatomic locations were broad involving all tissue planes, including skin (n=4), intraosseous (n=4), major salivary glands (n=2), sinonasal tract (n=2), soft tissue of face or neck (n=2), and oral cavity (n=1). The histologic spectrum ranged from benign to high grade, in descending order including tumors resembling malignant peripheral nerve sheath tumor (MPNST)-like, fibrosarcoma (infantile or adult-type), lipofibromatosis-like neural tumor (LPFNT), inflammatory myofibroblastic tumor-like, and a novel phenotype resembling myxoma. Perivascular hyalinization/stromal keloid-like collagen bands and staghorn vasculature were common features in MPNST-like and LPFNT-like tumors. Two tumors (1 each with NTRK1 or BRAF rearrangement) were classified as high grade. By immunohistochemistry, S100 and CD34 positivity was noted in 71% and 60%, frequently in MPNST-like and LPFNT-like phenotypes. Pan-TRK was a sensitive marker for NTRK-translocated tumors but was negative in tumor with other kinase fusions. One patient with a high-grade tumor developed distant metastasis. Molecular testing for various kinase fusions should be considered for S100+/CD34+ spindle cell neoplasms with perivascular hyalinization and staghorn vessels, as pan-TRK positivity is seen only in NTRK fusions.

GISTs with NTRK Gene Fusions: A Clinicopathological, Immunophenotypic, and Molecular Study

The most common mutations in gastrointestinal stromal tumors (GISTs) are KIT or PDGFRA mutations. Recently, neurotrophic tyrosine receptor kinase (NTRK) fusions have been reported in WT GISTs, which increased interest in introducing tropomyosin receptor kinase (TRK) inhibitors as treatments for GISTs with NTRK fusions. Hence, we aimed to screen NTRK fusions in WT GISTs; we used fluorescence in situ hybridization (FISH), next-generation sequencing (NGS), and immunohistochemistry (IHC) to screen NTRK fusions in 46 WT GISTs and evaluate each method. We further reviewed NTRK fusion-positive GISTs from the literature and performed clinical and pathological analyses; two GISTs with an ETV6-NTRK3 fusion (5%) were identified, while only one (50%) was positive for Pan-TRK expression. On the other hand, among the six GISTs with Pan-TRK-positive expression, only one (17%) harbored NTRK fusion. The literature review revealed the strong consistency between FISH and NGS and the limited value of Pan-TRK IHC in screening NTRK fusions in GISTs. In addition, the clinical and pathological analysis showed that GISTs with NTRK rearrangement occurred less frequently in the stomach, were more frequently larger in size, and the epithelioid type presented with a higher risk of recurrence. The NTRK3 fusion has been more common than the NTRK1 fusion in GISTs to date; our study identified two ETV6-NTRK3 fusions in 46 WT GISTs. Compared with FISH and IHC, NGS is preferred for screening WT GISTs, including NTRK rearrangements. However, since GISTs with NTRK fusions are rare, further studies including more samples and mechanistic investigations should be conducted in the future.

Congenital mesoblastic nephroma: review of current management and outcomes in a single centre

BACKGROUND

Congenital mesoblastic nephroma (CMN) is a rare tumour of the kidney with an overall excellent prognosis. Once considered a benign tumour, it is now recognized to carry a risk of recurrence and metastases with subsequent poor outcomes. The potential for genetic aberrations such as ETV6-NTRK3 fusion raises the potential for targeted treatments in certain patients. The optimum mode and frequency of surveillance is unclear. This study aims to assess this institution's experience with CMN and long-term outcomes.

METHODS

A single centre retrospective review was performed of all confirmed cases of CMN between October 2001 and January 2021.

RESULTS

Nine cases of CMN in patients under 12 months of age were identified. The histopathology, management and outcomes of these patients are discussed.

CONCLUSION

CMN overall has a very good prognosis, but a subgroup does exist that will have poor outcomes. It is difficult to accurately identify this group to target adjuvant therapy.

Treatment Patterns of Real-World Patients with TRK Fusion Cancer Treated by US Community Oncologists

BACKGROUND

Neurotrophic tyrosine receptor kinase (NTRK) gene fusions are present across various tumor types with an estimated overall prevalence of less than 1%. Tropomyosin receptor kinase inhibitors (TRKis) block the constitutively activated tyrosine receptor kinase (TRK) fusion protein produced in cancers with NTRK gene fusions (NTRK+) from downstream signaling. Many treatment guidelines now include TRKis as first-line (1L) or subsequent treatment options for TRK fusion cancer.

OBJECTIVE

This study aimed to assess treatment patterns subsequent to a finding of NTRK+ status among patients with TRK fusion cancer.

PATIENTS AND METHODS

This was a one-time, retrospective, multi-site patient chart abstraction by oncology practices in the USA from June to September 2020. US medical oncologists from the Oncology Provider Extended Network (OPEN) who had treated patients with NTRK+ advanced/metastatic solid tumors abstracted information into electronic case report forms (eCRFs) for adult patients with advanced/metastatic solid tumors and a NTRK+ tumor test result with a known fusion partner. Data abstracted into eCRFs by oncologists included demographic, clinical, and treatment characteristics of patients with advanced/metastatic TRK fusion solid tumors. Responses were summarized using descriptive statistics. Median treatment durations across the lines of therapy were estimated by Kaplan-Meier time to discontinuation.

RESULTS

A total of 19 medical oncologists abstracted data from 110 patient charts. Median patient age at advanced/metastatic diagnosis was 62 years. The majority of patients were male (58.2%) and White (79.1%). Solid tumor types reported in at least 10% of the study cohort were lung (24.5%), cholangiocarcinoma (13.6%), pancreatic (10.9%), and colorectal (10.0%). Results for patients with hepatobiliary cancers (i.e., cholangiocarcinoma, pancreatic cancer, hepatocellular carcinoma) and colorectal cancer, and appendiceal cancer are also included. Median duration of 1L TRKi therapy was 16.8 months across all solid tumor types, whereas median duration of 1L was 5.6 months among patients receiving non-TRKi therapies (p = 0.017). Among the solid tumor types represented by at least 10% of the study population, median duration of 1L TRKi therapy was only reached in patients with pancreatic cancer (3.3 months). Median duration of TRKi in the second-line (2L) setting was 7.9 months overall, relative to 5.3 months among patients receiving non-TRKi therapies (p = 0.003). Across lung, cholangiocarcinoma, pancreatic, and colorectal cancers, the median durations of 2L TRKi therapy were 14.1, 6.0, 6.1, and 4.1 months, respectively.

CONCLUSION AND RELEVANCE

Among patients with advanced/metastatic TRK fusion solid tumors, medical oncologists reported that approximately two-thirds initiated a TRKi during the study period. Treatment with a TRKi was longer in duration compared to non-TRKi treatment in 1L and 2L therapy. Additional research is needed to gain insight into the association between early TRKi therapy initiation and clinical outcomes in the real-world setting.

Update on prognostic and predictive biomarkers of breast cancer

Breast cancer represents a heterogeneous group of human cancer at both histological and molecular levels. Estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) are the most commonly used biomarkers in clinical practice for making treatment plans for breast cancer patients by oncologists. Recently, PD-L1 testing plays an important role for immunotherapy for triple-negative breast cancer. With the increased understanding of the molecular characterization of breast cancer and the emergence of novel targeted therapies, more potential biomarkers are needed for the development of more personalized treatments. In this review, we summarized several main prognostic and predictive biomarkers in breast cancer at genomic, transcriptomic and proteomic levels, including hormone receptors, HER2, Ki67, multiple gene expression assays, PD-L1 testing, mismatch repair deficiency/microsatellite instability, tumor mutational burden, PIK3CA, ESR1 andNTRK and briefly introduced the roles of digital imaging analysis in breast biomarker evaluation.

NTRK Fusions in 1113 Solid Tumors in a Single Institution

Most NTRK fusions occur at very low frequencies in various common cancers. Recent recommendations on NTRK testing recommend immunohistochemistry (IHC) as the initial test for tumor types with a low frequency of NTRK fusions. This study investigated the accuracy of an IHC assay to detect NTRK fusions and characterize the clinicopathological and molecular features of NTRK-rearranged tumors. This retrospective study was conducted on 1113 solid tumor samples known to harbor no oncogenic driver alterations, including 510 non-small cell lung cancers (NSCLC), 503 colorectal cancers (CRC), and 79 inflammatory myofibroblastic tumors (IMT). Additionally, 21 ALK expression-positive cases were included. TRK expression was evaluated using a pan-Trk IHC assay, and positive cases were validated using NGS. TRK expression was observed in three NSCLCs (0.6%), six CRCs (1.2%), and six IMTs (6%). NTRK fusions were finally detected in two NSCLCs (0.4%), six CRCs (1.2%), and one IMT (1%). In NSCLC and CRC, the majority of NTRK fusions were readily discernible due to diffuse moderate-to-strong cytoplasmic staining on pan-Trk IHC. In IMT, focal weak nuclear staining indicated the presence of NTRK fusion. Therefore, the utility of pan-Trk IHC should be assessed considering that the difference in performance depends on tumor type.

Primary Renal Sarcoma with SS18::POU5F1 Gene Fusion

We report the first case of a primary renal undifferentiated sarcoma harboring an SS18::POU5F1 gene fusion. The patient was a 38 year-old male diagnosed with a 5 cm renal tumor which invaded the adrenal gland and extended into the renal vein. Microscopically, the neoplasm had a predominantly undifferentiated round cell morphology, with areas of rhabdoid and spindle cell growth. Similar to the previously reported cases with this fusion, by immunohistochemistry the neoplasm expressed S100 protein and epithelial markers (diffuse EMA, focal cytokeratin), suggesting the possibility of a myoepithelial phenotype. This report documents another example of a fusion-positive undifferentiated soft tissue sarcoma occurring as a primary renal neoplasm, adding to the already broad list of such entities. It highlights the crucial role of molecular analysis in establishing a specific diagnosis given the overlapping morphology and immunophenotypes such entities may exhibit. This article is protected by copyright. All rights reserved.

Secretory Carcinoma of the Salivary Gland: A Rarity in Children

Originally described as mammary analog secretory carcinoma (SC), SC of the salivary gland is a rare malignancy with morphologic and molecular similarities to SC of the breast. We present 2 children with salivary gland SC with the classic ETV6-NTRK3 gene fusion, including 1 with lymph node metastases. Both patients underwent surgical resection and were in remission 24 months postsurgery. One patient was additionally found to have synchronous papillary thyroid carcinoma with a TFG-MET fusion. A review of published cases highlights the expanding molecular profile and confirms the favorable course of salivary gland SC after surgical resection.

Detection of NTRK Fusions and TRK Expression and Performance of pan-TRK Immunohistochemistry in Routine Diagnostics: Results from a Nationwide Community-Based Cohort

Gene fusions involving NTRK1, NTRK2, and NTRK3 are rare drivers of cancer that can be targeted with histology-agnostic inhibitors. This study aimed to determine the nationwide landscape of NTRK/TRK testing in the Netherlands and the usage of pan-TRK immunohistochemistry (IHC) as a preselection tool to detect NTRK fusions. All pathology reports in 2017–2020 containing the search term ‘TRK’ were retrieved from the Dutch Pathology Registry (PALGA). Patient characteristics, tumor histology, NTRK/TRK testing methods, and reported results were extracted. NTRK/TRK testing was reported for 7457 tumors. Absolute testing rates increased from 815 (2017) to 3380 (2020). Tumors were tested with DNA/RNA-based molecular assay(s) (48%), IHC (47%), or in combination (5%). A total of 69 fusions involving NTRK1 (n = 22), NTRK2 (n = 6) and NTRK3 (n = 41) were identified in tumors from adult (n = 51) and pediatric (n = 18) patients. In patients tested with both IHC and a molecular assay (n = 327, of which 29 NTRK fusion-positive), pan-TRK IHC had a sensitivity of 77% (95% confidence interval (CI), 56–91) and a specificity of 84% (95% CI, 78–88%). These results showed that pan-TRK IHC has a low sensitivity in current routine practice and warrants the introduction of quality guidelines regarding the implementation and interpretation of pan-TRK IHC.

NTRK Fusions Detection in Paediatric Sarcomas to Expand the Morphological Spectrum and Clinical Relevance of Selected Entities

Undifferentiated round cell sarcomas (URCS) of soft tissue and bone and tumours of uncertain differentiation (TUD) are commonly ascribed to a subset of neoplasms with low frequency of NTRK gene fusions. However, more recently NTRK-rearranged round and spindle cell tumours have been noted in case reports and in limited or heterogeneous cohorts. The aim of our study was to investigate the presence of NTRK gene fusions in a large retrospective cohort of paediatric URCS and TUD after a systematic review of the diagnosis, according to the recently updated WHO classification scheme. One-hundred and five patients with diagnosis of URCS or TUD, involving the bone or soft tissue, were retrospectively evaluated. After the case selection and the histopathological review of the case cohort, pan-Trk immunohistochemistry (IHC) testing was performed on formalin-fixed paraffin-embedded (FFPE) tissues. Tumour RNA was extracted from FFPE tissue and subjected to next-generation sequencing (NGS) library preparation, using a 10-gene NGS fusion panel, sequenced on an Illumina MiSeq. The NGS-positive cases were further confirmed by real-time PCR. On immunohistochemical screening, 12/105 (11.4%) cases were positive using the pan-Trk antibody, showing three different staining patterns with the cytoplasmic distribution being most common. Molecular analysis using NGS and confirmed by the real-rime PCR detected two positive cases for the ETV6-NTRK3 fusion. The histological pattern of the two positive cases, together with the demonstration of the NTRK rearrangement, leaded to re-classify these previously not otherwise specified sarcomas with uncertain differentiation into the emerging category of NTRK-rearranged neoplasms. In addition, we found the two NTRK fused neoplasms showing a clinical indolent course, in contrast with literature.

New Approaches with Precision Medicine in Adult Brain Tumors

Primary central nervous system (CNS) tumors represent a heterogenous group of tumors. The 2021 fifth edition of the WHO Classification of Tumors of the CNS emphasizes the advanced role of molecular diagnostics with routine implementation of molecular biomarkers in addition to histologic features in the classification of CNS tumors. Thus, novel diagnostic methods such as DNA methylome profiling are increasingly used to provide a more precise diagnostic work-up of CNS tumors. In addition to these diagnostic precision medicine advantages, molecular alterations are also addressed therapeutically with targeted therapies. Like in other tumor entities, precision medicine has therefore also arrived in the treatment of CNS malignancies as the application of targeted therapies has shown promising response rates. Nevertheless, large prospective studies are currently missing as most targeted therapies were evaluated in single arm, basket, or platform trials. In this review, we focus on the current evidence of precision medicine in the treatment of primary CNS tumors in adults. We outline the pathogenic background and prevalence of the most frequent targetable genetic alterations and summarize the existing evidence of precision medicine approaches for the treatment of primary CNS tumors.

Recent Advances on Immunohistochemistry and Molecular Biology for the Diagnosis of Adnexal Sweat Gland Tumors

Simple Summary

Cutaneous sweat gland tumors form an extremely diverse and heterogeneous group of neoplasms that show histological differentiation to the sweat apparatus. Due to their rarity, wide diagnostic range, and significant morphological overlap between entities, their accurate diagnosis remains challenging for pathologists. Until recently, little was known about the molecular pathogenesis of adnexal tumors. Recent findings have revealed a wide range of gene fusions and other oncogenic factors that can be used for diagnostic purposes and, for some, can be detected by immunohistochemistry. Among other organs containing exocrine glands, such as salivary glands, breasts, and bronchi, most of these biomarkers have been reported in homologous neoplasms that share morphological features with their cutaneous counterparts. This review aims to describe these recent molecular and immunohistochemical biomarkers in the field of sweat gland tumors.

Abstract

Cutaneous sweat gland tumors are a subset of adnexal neoplasms that derive or differentiate into the sweat apparatus. Their great diversity, rarity, and complex terminology make their pathological diagnosis challenging. Recent findings have revealed a wide spectrum of oncogenic drivers, several of which are of diagnostic interest for pathologists. Most of these molecular alterations are represented by gene fusions, which are shared with other homologous neoplasms occurring in organs containing exocrine glands, such as salivary and breast glands, which show similarities to the sweat apparatus. This review aims to provide a synthesis of the most recent immunohistochemical and molecular markers used for the diagnosis of sweat gland tumors and to highlight their relationship with similar tumors in other organs. It will cover adenoid cystic carcinoma (NFIB, MYB, and MYBL1 fusion), cutaneous mixed tumor (PLAG1 fusion), cylindroma and spiradenoma and their carcinomas thereof (NF-κB activation through CYLD inactivation or ALKP1 hotspot mutation), hidradenoma and hidradenocarcinoma (MAML2 fusion), myoepithelioma (EWSR1 and FUS fusion), poroma and porocarcinoma (YAP1, MAML2, and NUTM1 fusion), secretory carcinoma (ETV6, NTRK3 fusion), tubular adenoma and syringo-cystadenoma papilliferum (HRAS and BRAF activating mutations). Sweat gland tumors for which there are no known molecular abnormalities will also be briefly discussed, as well as potential future developments.

Rational drug design to explore the structure-activity relationship (SAR) of TRK inhibitors with 2,4-diaminopyrimidine scaffold

Tropomyosin receptor kinase (TRK) is an ideal target for treating cancers caused by the NTRK gene fusion. In this study, more than 60 2,4-diaminopyrimidine derivatives were prepared to understand the structure-activity relationship and confirm the rationality of the pharmacophore model reported previously. Among them, compound 19k was found to be a potent pan-TRK inhibitor that inhibits the proliferation of Km-12 cell lines. Additionally, compound 19k induced the apoptosis of Km-12 cells in a concentration-dependent manner. Western blot analysis revealed that compound 19k inhibited the phosphorylation of TRK to block downstream pathways. Compound 19k also possessed outstanding plasma stability and liver microsomal stability in vitro, with half-lives greater than 289.1 min and 145 min, respectively. Pharmacokinetic studies indicated that the oral bioavailability of compound 19k is 17.4%. These results demonstrate that compound 19k could serve as a novel lead compound for overcoming NTRK-fusion cancers.

Genitourinary Tract Tumors in Children: An Update

BACKGROUND

Genitourinary tract tumors in children are less common than in adults. Most of these tumors have different genetic backgrounds, clinical presentation, and oncologic behavior than their adult counterpart. As a result of low prevalence in children, some of the treatment approaches and recommendations are based on treatment experience in adult patients. However, thanks to scientific and technological development, survival rates have risen considerably.

OBJECTIVE

This paper presents a review of the principal features of the tumors involving the genitourinary tract in children and an update in genetic background, diagnosis, and treatment.

METHODS

A narrative review was performed on published literature about genitourinary tract tumors in pediatric patients. Papers presented in English and Spanish literature were reviewed. PubMed, Science Direct, and SciELO databases were used to collect information and present this article.

RESULTS

Kidney tumors are the most common type of genitourinary tumors in children. Among those, Wilms tumor represents the majority of cases and shows the successful work of clinical trial groups studying this tumor type. Other tumors involving the genitourinary tract in children include Rhabdomyosarcoma, Transitional cell carcinoma, Testicular, and Adrenal tumors.

CONCLUSION

Genitourinary tract tumors in children represent significant morbidity and economic burden, so awareness in early diagnosis represents improvement in treatment, clinical, and oncological outcomes.

The promise of TRK inhibitors in pediatric cancers with NTRK fusions

NTRK fusions are rare oncogenic drivers that occur across a range of pediatric cancers. These include infantile fibrosarcoma and secretory breast cancer in which such fusions are nearly pathognomonic, and a spectrum of more common pediatric cancers in which NTRK fusions occur at a lower frequency. Within the last 5 years, two TRK inhibitors, larotrectinib and entrectinib, have demonstrated histology-agnostic activity against NTRK fusion driven cancers and achieved FDA approval. Here the data supporting the use of these TRK inhibitors for the treatment of cancers harboring NTRK fusions is reviewed, with a particular focus on the pediatric experience. Mechanisms of acquired resistance to these first generation TRK inhibitors are discussed and investigational second generation TRK inhibitors that may overcome some of these mechanisms of resistance are highlighted.

Fusion-Positive Salivary Gland Carcinomas

Salivary gland tumors are a rare, heterogeneous group of neoplasms that pose significant diagnostic challenges for the histopathologist. Histopathological diagnosis relies primarily on morphological assessment, with ancillary special stains and immunohistochemistry. In recent years, new defining genomic alterations have been characterized in these tumors. In particular, they include gene fusions which have shown to be tightly tumor-type specific, and thus valuable for use in diagnostically challenging cases. These discoveries also help in refining tumor classification. Furthermore, such genetic alterations may have prognostic as well as potentially therapeutic implications in the era of personalized medicine. This review aims at providing a summary of the most recent updates in this field.

Cytopathological Findings of Secretory Carcinoma of the Salivary Gland and the Diagnostic Utility of Giemsa Staining

Secretory carcinoma is a salivary gland neoplasm first described as a mammary analogue secretory carcinoma by Skalova and redesignated as a secretory carcinoma in the 2017 World Health Organization Classification of Head and Neck Tumors. Secretory carcinoma diagnosis is reliant on specific cytological and histological findings and the detection of an ETV6-NTRK3 fusion gene. Here, we examined the clinical and cytopathological features of four cases of secretory carcinoma occurring in three males and a female, aged between 39 and 74 years. All four tumors involved the parotid gland, and were found to have the ETV6-NTRK3 fusion gene. Fine-needle aspiration-based cytology smears of all tumors displayed papillary and/or dendritic pattern clusters, some of which were associated with blood vessels. The neoplastic cells displayed enlarged nuclei with fine chromatin and small, distinct, single nucleoli. Furthermore, several neoplastic cells with a characteristic vacuolated cytoplasm were identified in each specimen. Giemsa staining revealed cytoplasmic vacuolation, intracytoplasmic metachromatic secretions and/or various sized metachromatic granules, and a background of metachromatic mucin in all four specimens. Given this, we conclude that these cytological findings, especially those of the Giemsa staining, might be helpful in the diagnosis of secretory carcinoma.

An unusual fusion gene EML4-ALK in a patient with congenital mesoblastic nephroma

Congenital mesoblastic nephroma (CMN), the most common renal tumor of infancy, is a mesenchymal neoplasm histologically classified into classic, cellular, or mixed types. Most cellular CMNs harbor a characteristic ETV6-NTRK3 fusion. Here, we report an unusual congenital mesoblastic nephroma presenting in a newborn boy with a novel EML4-ALK gene fusion revealed by Anchored Multiplex RNA Sequencing Assay. The EML4-ALK gene fusion expands the genetic spectrum implicated in the pathogenesis of congenital mesoblastic nephroma, with yet another example of kinase oncogenic activation through chromosomal rearrangement. The methylation profile of the tumor corresponds with infantile fibrosarcoma showing the biological similarity of these two entities.

Expanding the Spectrum of EWSR1-NFATC2-rearranged Benign Tumors: A Common Genomic Abnormality in Vascular Malformation/Hemangioma and Simple Bone Cyst

A simple bone cyst (SBC) is a cystic bone lesion predominantly affecting young males. The cyst is lined by a fibrous membrane and filled with serosanguinous fluid. EWSR1/FUS-NFATC2 rearrangements were recently identified in SBC. We here report exactly the same rearrangement in 3 lesions diagnosed as vascular malformations of 2 elderly patients. In total, through Archer FusionPlex, fluorescence in situ hybridization and/or reverse transcriptase-polymerase chain reaction the EWSR1-NFATC2 rearrangement was identified in 6 of 9 SBC, 3 of 12 benign vascular tumors, and none of 5 aneurysmal bone cyst lacking USP6 fusion. Using fluorescence in situ hybridization, it was apparent that amplification of the fusion, as seen in EWSR1-NFATC2 round cell sarcomas, was absent, and that in the vascular tumors the fusion was present both in the lining cells as well as in the surrounding spindle cells. Of note, not all of the spaces in the vascular malformations were lined by endothelial cells. Aggrecan was positive in all cases but was not specific. NKX2-2 and NKX3-1 staining were negative in all cases. Thus, even though the overlap between the 2 entities is limited to the presence of few thick-walled cysts lacking endothelial lining in the benign vascular malformations, the spectrum of benign tumors containing NFATC2 fusions should be expanded and contains not only SBC in the young, but also vascular malformation/hemangioma in elderly 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.

NTRK-rearranged papillary thyroid carcinoma demonstrates frequent subtle nuclear features and indeterminate cytologic diagnoses

BACKGROUND

The studies on the cytomorphologic features of NTRK-rearranged papillary thyroid carcinoma (PTC) are limited and some reported characteristics, such as frequent indeterminate diagnoses and presence of fibrotic fragments, are inconsistent in literature.

METHODS

NTRK gene rearrangements were detected in thyroidectomy specimens of PTC by either fluorescence in situ hybridization or next-generation sequencing. All the cytologic slides of NTRK-rearranged PTC were reviewed to evaluate the cytomorphologic features. The preoperative cytologic diagnoses of NTRK-rearranged PTC were compared with those of NTRK/BRAF wild-type and BRAF^V600E -positive PTC.

RESULTS

Fourteen PTC cases were identified to harbor NTRK gene rearrangements. Most of them showed a mixed architectural pattern of cell fragments (n = 13, 92.9%) and microfollicles (n = 9, 64.3%) with relatively rare papillary structures (n = 4, 28.6%). Nuclear grooving was frequently present (n = 11, 78.6%) but was mostly subtle and limited. Seven cases (50.0%) showed rounded nuclei without discernible nuclear elongation, and only 3 (21.4%) cases presented with nuclear pseudoinclusions. Among these cases, 7 (50.0%) were diagnosed as The Bethesda System for Reporting Thyroid Cytopathology (TBS) category III, 2 (14.3%) were diagnosed as TBS IV, and 5 (35.7%) were diagnosed as TBS V. The rate of TBS III-IV diagnoses for NTRK-rearranged PTCs was significantly higher (64.3%) than that for the 25 consecutive NTRK/BRAF wild-type PTCs (20.0%, P = .013) and the 70 consecutive BRAF^V600E -positive PTCs (7.1%, P < .001) as selected.

CONCLUSIONS

NTRK-rearranged PTC demonstrated intermediate nuclear features, such as subtle nuclear grooving, infrequent nuclear elongation, and rare pseudoinclusions, resulting in a significantly higher rate of TBS III-IV diagnoses compared to PTC with other molecular alterations.

[Multidisciplinary consensus on optimizing the detection of NTRK gene alterations in tumours]

The recent identification of rearrangements of neurotrophic tyrosine receptor kinase (NTRK) genes and the development of specific fusion protein inhibitors, such as larotrectinib and entrectinib, have revolutionized the diagnostic and clinical management of patients presenting with tumours with these alterations. Tumours that harbour NTRK fusions are found in both adults and children and are either rare tumours with common NTRK fusions that may be diagnostic, or more common tumours with rare NTRK fusions. To assess the currently available evidence, 3key Spanish medical societies (the Spanish Society of Medical Oncology (SEOM), the Spanish Society of Pathology (SEAP) and the Spanish Society of Paediatric Haematology and Oncology (SEHOP) have brought together a group of experts to develop a consensus document that includes guidelines on the diagnostic, clinical and therapeutic aspects of NTRK-fusion tumours. It also discusses the challenges related to the routine detection of these genetic alterations in a mostly public health care system.

Clinicopathologic and Molecular Characterization of Four Cases of Pediatric Salivary Secretory Carcinoma (SSC), One with ETV6-RET Fusion

Salivary gland secretory carcinoma (SSC) is a neoplasm with characteristic histologic features, similar to those of secretory carcinoma of the breast. Only a few pediatric SSC cases have been reported, all with ETV6-NTRK3 fusion. We present four new pediatric SSC examples, one with a novel ETV6-RET fusion. Four cases of SSC were diagnosed between 2010 and 2020: 2 boys, 7 and 9 year-old with parotid tumors (1.5 and 1.3 cm, respectively); and two 14 year-old girls: one with a submandibular tumor (2.1 cm), and one with a parotid lesion (1.2 cm). Histologically, all tumors were similar: well-circumscribed lesions composed by mid-size, monotonous cells with eosinophilic and sometimes vacuolated cytoplasm. The nuclei are oval to round with open chromatin and a single nucleolus. There are duct-like structures and microcysts with colloid-like material. Immunohistochemically, tumor cells are positive for S100, CK7, mammaglobin and GATA3. A classic ETV6-NTRK3 translocation was confirmed in the three parotid tumors; an ETV6-RET fusion was demonstrated in the submandibular lesion. All patients underwent complete surgical resection and are alive without tumor recurrence after a follow-up time ranging from one to 4 years. Pediatric SSC is extremely rare but their characteristic morphology and immunohphenotype facilitate their diagnosis. We describe the first pediatric case with the recently reported ETV6-RET fusion. Similar to adult cases, this tumor is morphologically undistinguishable from those carrying the classic ETV6-NTRK3 translocation. Thus, in pediatric cases with morphology suggestive of SSC and negative ETV6-NTRK3 by RT-PCR, other possible fusions should be investigated.

Novel fusion sarcomas including targetable NTRK and ALK

BACKGROUND

Challenging emerging entities with distinctive molecular signatures may benefit from algorithms for diagnostic work-up.

METHODS

Fusion sarcomas (2020-2021, during pandemic) were diagnosed by clinicoradiology, morphology, phenotype, and next-generation sequencing (NGS).

RESULTS

Six fusion sarcomas in two males and four females involved the chest-wall, neck, or extremities; ages ranged 2-73, median 18 years. Sizes ranged 5.3-25.0, median 9.1 cm. These include high grade 1) TPR-NTRK1 of proximal femur with a larger rounded soft tissue mass, previously considered osteosarcoma yet without convincing tumor matrix. A pathologic fracture necessitated emergency hemipelvectomy (NED) and 2) novel KANK1-NTRK2 sarcoma of bone and soft tissue with spindled pleomorphic to epithelioid features (AWD metastases). 3) Novel ERC1-ALK unaligned fusion, a low grade infiltrative deep soft tissue hand sarcoma with prominent-vascularity, myopericytoid/lipofibromatosis-like ovoid cells, and collagenized stroma, was successfully treated with ALK-inhibitor (Crizotinib), avoiding amputation. These NTRK and ALK tumors variably express S100 and CD34 and were negative for SOX10. 4) and 5) CIC-DUX4 round cell tumors (rapid metastases/demise), one with COVID superinfection, were previously treated as Ewing sarcoma. These demonstrated mild pleomorphism and necrosis, variable myxoid change and CD99 reactivity, and a distinctive dot-like-Golgi WT1 immunostaining pattern. 6) A chest wall/thoracic round cell sarcoma, focal CD34/ keratins/CK7, revealed nuclear-STAT6, STAT6-NAB2 by NGS, confirming malignant solitary fibrous tumor, intermediate-risk-stratification (AWD metastases).

CONCLUSIONS

Recent fusion sarcomas include new KANK1-NTRK2 and ERC1-ALK, the latter successfully treated by targeted-therapy. ALK/NTRK fusion partners TPR and KANK1 suggest unusual high-grade morphology/behavior. Clinicoradiologic, morphologic, and phenotypic algorithms can prompt molecular-targeted immunostains or NGS for final classification and promising inhibitor therapy.