Kinase expression in angiomatoid fibrous histiocytoma: panTRK is commonly expressed in the absence of NTRK rearrangement.

Angiomatoid fibrous histiocytoma (AFH) is a soft tissue tumour of intermediate (rarely metastasising) malignant potential, which harbours EWSR1/FUS gene fusions. These tumours can express anaplastic lymphoma kinase (ALK) in the absence of gene rearrangement or copy number alteration and can also coexpresses Pan-TRK immunohistochemistry (IHC). All EWSR1/FUS-rearranged AFH were retrieved from the files of three institutions and Pan-TRK (EPR17341), ALK and BRAF V600E IHC were performed. Fourteen AFH cases were identified, which included three cases of intracranial mesenchymal tumours with FET-CREB fusions. PanTRK and ALK positive immunostaining was identified in 9 (64.2%) and 12 (85.7%) cases, respectively. No NTRK or ALK translocations or increased copy number/amplification were identified in all eight cases which had fluorescence in situ hybridisation and/or next generation sequencing for NTRK1-3 and ALK available for assessment. None of the cases expressed BRAF-V600E.Although our study is limited, our report is the first to document PanTRK expression in AFH in the absence of identifiable NTRK1-3 gene alterations.

Zoledronic Acid Add-on Therapy for Standard-Risk Ewing Sarcoma Patients in the Ewing 2008R1 Trial.

PURPOSE: The phase III, open-label, prospective, multicenter, randomized Ewing 2008R1 trial (EudraCT2008-003658-13) was conducted in 12 countries to evaluate the effect of zoledronic acid (ZOL) maintenance therapy compared with no add-on regarding event-free survival (EFS, primary endpoint) and overall survival (OS) in standard-risk Ewing sarcoma (EWS). PATIENTS AND METHODS: Eligible patients had localized EWS with either good histologic response to induction chemotherapy and/or small tumors (<200 mL). Patients received six cycles of VIDE induction and eight cycles of VAI (male) or eight cycles of VAC (female) consolidation. ZOL treatment started parallel to the sixth consolidation cycle. Randomization was stratified by tumor site (pelvis/other). The two-sided adaptive inverse-normal four-stage design (planned sample size 448 patients, significance level 5%, power 80%) was changed after the first interim analysis using the Müller-Schäfer method. RESULTS: Between April 2010 and November 2018, 284 patients were randomized (142 ZOL/142 no add-on). With a median follow-up of 3.9 years, EFS was not significantly different between ZOL and no add-on group in the adaptive design (HR, 0.74; 95% CI, 0.43-1.28, P = 0.27, intention-to-treat). Three-year EFS rates were 84.0% (95% CI, 77.7%-90.8%) for ZOL vs. 81.7% (95% CI, 75.2%-88.8%) for no add-on. Results were similar in the per-protocol collective. OS was not different between groups. The 3-year OS was 92.8% (95% CI, 88.4%-97.5%) for ZOL and 94.6% (95% CI, 90.9%-98.6%) for no add-on. Noticeable more renal, neurologic, and gastrointestinal toxicities were observed for ZOL (P < 0.05). Severe renal toxicities occurred more often in the ZOL arm (P = 0.003). CONCLUSIONS: In patients with standard-risk localized EWS, there is no additional benefit from maintenance treatment with ZOL.

Increased Bone Formation and Accelerated Bone Mass Accrual in a Man Presenting with Diffuse Osteosclerosis/High Bone Mass Phenotype and Adenocarcinoma of Unknown Primary.

A 71-year-old man was referred for evaluation of incidental generalized osteosclerosis. He was found to have a high bone mass (HBM) with an elevated lumbar spine bone mineral density (BMD) Z-score of +5.3. Over an 18-month period, his lumbar spine BMD measured by dual energy X-ray absorptiometry (DXA) had increased by +64% from 1.09 to 1.79 g/cm2 and femoral neck by +21% from 0.83 to 1.01 g/cm2. Biochemical markers of bone turnover were markedly increased (serum propeptide of type 1 collagen and urine telopeptides greater than 10-times normal). The high bone formation and increased skeletal calcium acquisition resulted in profound hypocalcemia (low serum calcium 1.88 mmol/L) and hypocalciuria (low urinary calcium <0.2 mmol/day). Positron emission tomography (PET) with 2-deoxy-2-[fluorine-18] fluoro-D-glucose (FDG) confirmed diffuse osteosclerosis without focal areas of abnormal FDG uptake in the skeleton or elsewhere to suggest either an underlying primary malignancy or metastatic disease. Bone biopsy showed markedly sclerotic woven and lamellar bone. The marrow space was devoid of typical bone cells and adipocytes and instead was filled by fibromyxoid stroma, infiltrated by small clusters of tumor cells. Bone histomorphometry and micro-computed tomography demonstrated an elevated trabecular bone volume and trabecular plate thickness. The bone disorder in this case is unique and raises the possibility of a new yet undefined novel anabolic paracrine factor (or factors) secreted by an adenocarcinoma of unknown primary that resulted in dramatic increases in BMD, HBM, and radiological osteosclerosis. The differential diagnosis and potential mechanisms responsible for the HBM are discussed. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Improving sarcoma classification by using RNA hybridisation capture sequencing in sarcomas of uncertain histogenesis of young individuals.

Our aim was to utilise a 241-gene RNA hybridisation capture sequencing (CaptureSeq) gene panel to identify unexpected fusions in undifferentiated, unclassified or partly classified sarcomas of young individuals (<40 years). The purpose was to determine the utility and yield of a large, targeted fusion panel as a tool for classifying tumours that do not fit typical diagnostic entities at the time of the original diagnosis. RNA hybridisation capture sequencing was performed on 21 archival resection specimens. Successful sequencing was obtained in 12 of 21 samples (57%), two of which (16.6%) harboured translocations. A novel NEAT1::GLI1 fusion, not previously reported in the literature, presented in a young patient with a tumour in the retroperitoneum, which displayed low grade epithelioid cells. The second case, a localised lung metastasis in a young male, demonstrated a EWSR1::NFATC2 translocation. No targeted fusions were identified in the remaining 83.4% (n=10) of cases. Forty-three per cent of the samples failed sequencing as a result of RNA degradation. RNA-based sequencing is an important tool, which helps to redefine the classification of unclassified or partly classified sarcomas of young adults by identifying pathogenic gene fusions in up to 16.6% of the cases. Unfortunately, 43% of the samples underwent significant RNA degradation, falling below the sequencing threshold. As CaptureSeq is not yet available in routine pathology practice, increasing awareness of the yield, failure rate and possible aetiological factors for RNA degradation is fundamental to maximise laboratory procedures to improve RNA integrity, allowing the potential identification of significant gene alterations in solid tumours.

Immunohistochemistry for FOSB and FOS is a Useful Ancillary Tool in the Diagnosis of Epithelioid Hemangioma but There are Pitfalls in Interpretation Including Expression in Other Vascular Lesions.

Introduction. Epithelioid hemangioma is a benign vascular neoplasm associated with FOS and/or FOSB protein overexpression detected by immunohistochemistry (IHC). Methods. The aim of our study was to determine the co-expression or independent IHC expression of FOS and FOSB in a cohort of epithelioid hemangiomas. We also included two cohorts of other vascular lesions: papillary endothelial hyperplasia and lobular capillary hemangioma / pyogenic granuloma. Results. We identified 50 cases of epithelioid hemangioma, 84% of which were cutaneous and the remaining involved other anatomic locations. Over two thirds of all cases expressed FOSB (68%; 34/50) while FOS immunoreactivity was identified in 46% of all cases. Co-expression of FOSB and FOS occurred in 37% of cases while 76% of all cases stained for at least one of the antibodies. Fifty-eight percent (n = 14/24) and 33% (8/24) of all cases of papillary endothelial hyperplasia expressed FOS and FOSB, respectively. Thirty-two per cent of lobular capillary hemangiomas (n = 8/25) were positive for either FOS or FOSB. Conclusion. In summary, we present the largest cohort of epithelioid hemangiomas assessed with both FOS and FOSB and demonstrated that the use of both antibodies increases the detection rate of these proliferations by 10%. Nonetheless, the use of thresholds may not be appropriate, as only a subset of lesional endothelial cells label with FOS/FOSB. Over half of all cases of papillary endothelial hyperplasia and a third of lobular capillary hemangiomas also displayed immunoreactivity with FOS and/or FOSB.

High-Dose Treosulfan and Melphalan as Consolidation Therapy Versus Standard Therapy for High-Risk (Metastatic) Ewing Sarcoma.

PURPOSE: Ewing 2008R3 was conducted in 12 countries and evaluated the effect of treosulfan and melphalan high-dose chemotherapy (TreoMel-HDT) followed by reinfusion of autologous hematopoietic stem cells on event-free survival (EFS) and overall survival in high-risk Ewing sarcoma (EWS). METHODS: Phase III, open-label, prospective, multicenter, randomized controlled clinical trial. Eligible patients had disseminated EWS with metastases to bone and/or other sites, excluding patients with only pulmonary metastases. Patients received six cycles of vincristine, ifosfamide, doxorubicin, and etoposide induction and eight cycles of vincristine, actinomycin D, and cyclophosphamide consolidation therapy. Patients were randomly assigned to receive additional TreoMel-HDT or no further treatment (control). The random assignment was stratified by number of bone metastases (1, 2-5, and > 5). The one-sided adaptive-inverse-normal-4-stage-design was changed after the first interim analysis via Müller-Schäfer method. RESULTS: Between 2009 and 2018, 109 patients were randomly assigned, and 55 received TreoMel-HDT. With a median follow-up of 3.3 years, there was no significant difference in EFS between TreoMel-HDT and control in the adaptive design (hazard ratio [HR] 0.85; 95% CI, 0.55 to 1.32, intention-to-treat). Three-year EFS was 20.9% (95% CI, 11.5 to 37.9) in TreoMel-HDT and 19.2% (95% CI, 10.8 to 34.4) in control patients. The results were similar in the per-protocol collective. Males treated with TreoMel-HDT had better EFS compared with controls: median 1.0 years (95% CI, 0.8 to 2.2) versus 0.6 years (95% CI, 0.5 to 0.9); P = .035; HR 0.52 (0.28 to 0.97). Patients age < 14 years benefited from TreoMel-HDT with a 3-years EFS of 39.3% (95% CI, 20.4 to 75.8%) versus 9% (95% CI, 2.4 to 34); P = .016; HR 0.40 (0.19 to 0.87). These effects were similar in the per-protocol collective. This observation is supported by comparable results from the nonrandomized trial EE99R3. CONCLUSION: In patients with very high-risk EWS, additional TreoMel-HDT was of no benefit for the entire cohort of patients. TreoMel-HDT may be of benefit for children age < 14 years.

Revisiting the Case of Sarah Newbury's Death from Mollities Ossium.

Multiple myeloma and its precursor and variant types represent some of the most common hematologic malignancies in adults. These plasma cell dyscrasias are well-known in modern medicine. There are well-established clinical, laboratory, and pathologic criteria for diagnosis and staging. There is debate about the diagnosis of some of the earliest cases of myeloma described in the literature. We present a critical review of one such case.

Systemic treatments and outcomes in CIC-rearranged Sarcoma: A national multi-centre clinicopathological series and literature review.

CIC-rearranged sarcoma is a recently established, ultra-rare, molecularly defined sarcoma subtype. We aimed to further characterise clinical features of CIC-rearranged sarcomas and explore clinical management including systemic treatments and outcomes. METHODS: A multi-centre retrospective cohort study of patients diagnosed between 2014-2019. RESULTS: Eighteen patients were identified. The median age was 27 years (range 13-56), 10 patients were male (56%), 11 patients (61%) had localised disease and 7 patients had advanced (metastatic or unresectable) disease at diagnosis. Of 11 patients with localised disease at diagnosis, median overall survival (OS) was 40.6 months and the 1-, 2- and 5-year OS estimates were 82%, 64% and 34% respectively. Nine patients (82%) underwent surgery (all had R0 resections), 8 (73%) patients received radiotherapy to the primary site (median dose 57Gy in 28 fractions), and 8 (73%) patients received chemotherapy (predominantly Ewing-based regimens). Metastases developed in 55% with a median time to recurrence of 10.5 months. In patients with advanced disease at diagnosis, median OS was 12.6 months (95% CI 5.1-20.1), 1-year OS was 57%. Median progression-free survival was 5.8 months (95% CI 4.5-7.2). Durable systemic therapy responses occurred infrequently with a median duration of systemic treatment response of 2.1 months. One durable complete response of metastatic disease to VDC/IE chemotherapy was seen. Responses to pazopanib (n = 1) and pembrolizumab (n = 1) were not seen. CONCLUSION: In this series, CIC-rearranged sarcomas affected young adults and had a high incidence of presenting with, or developing, metastatic disease. The prognosis overall was poor. In advanced disease, durable systemic therapy responses were infrequent.

Lessons learnt from MDM2 fluorescence in-situ hybridisation analysis of 439 mature lipomatous lesions with an emphasis on atypical lipomatous tumour/well-differentiated liposarcoma lacking cytological atypia.

AIMS: Amplification of the murine double minute-2 (MDM2) gene, which is usually detected with fluorescence in-situ hybridisation (FISH), is the key driving event for atypical lipomatous tumours (ALTs)/well-differentiated liposarcomas (WDLs). We sought to determine the concordance between the histopathological findings and MDM2 FISH in the diagnosis of ALT/WDL, and to identify the histological features of MDM2-amplified tumours lacking classic atypia. METHODS AND RESULTS: We performed a retrospective analysis of all mature lipomatous lesions subjected to MDM2 FISH analysis at our institution. MDM2 FISH analysis was performed on 439 mature lipomatous lesions: 364 (82.9%) were negative and 75 (17%) were positive. In 17 of 75 (22.6%) ALTs/WDLs, cytological atypia was not identified on initial histological assessment, thus favouring lipoma. On review, these cases shared common histological features, consisting of a very low number of relatively small stromal cells within the tumour lobules, with mildly coarse chromatin and oval nuclei, admixed with unremarkable adipocytes in a tumour background devoid of fibroconnective septa, areas of fibrosis, or blood vessels. These cells matched the cells in which FISH showed MDM2 amplification. In contrast, 13 cases (3.5%) regarded as suspicious for ALT/WDL on the basis of histology lacked MDM2 amplification and were reclassified following the FISH findings. CONCLUSIONS: We conclude that a subset of lipoma-like ALTs/WDLs are not associated with any of the features typically described in ALT/WDL. Our study also showed that tumours >100 mm are more likely to be ALT/WDL; however, a history of recurrence or concerning clinical/radiological features was not significantly associated with classification as ALT/WDL.

Chromosome 8 Polysomy Accounting for MYC Over-Expression in Angiosarcoma Arising as Somatic-Type Malignancy in Metastatic Teratoma. Case Report.

MYC over-expression by immunohistochemistry (IHC) is utilised in routine pathology practice as a surrogate marker for MYC amplification, which plays a key oncogenic role in post-irradiation and chronic lymphedema-associated angiosarcoma. We present the case of a 32-year old male, who presented with high-grade angiosarcoma arising in a background of metastatic testicular teratoma. IHC for MYC showed strong nuclear expression in the angiosarcoma cells prompting the consideration of post-irradiation-induced angiosarcoma but our patient did not undergo radiotherapy. Fluorescence in-situ hybridization (FISH) excluded MYC amplification and instead showed Chromosome 8 polysomy, which accounted for the strong MYC IHC expression present, not previously described in the context of germ cell tumours. The occurrence of MYC over-expression due to polysomy illustrates a novel clinical scenario (angiosarcoma arising as somatic malignancy) where strong MYC IHC expression can be found in the absence of underlying amplification or prior radiotherapy exposure.

NKX3.1 immunohistochemistry is highly specific for the diagnosis of mesenchymal chondrosarcomas: experience in the Australian population.

Mesenchymal chondrosarcoma (MC) is a rare sarcoma that typically arises in adolescents and young adults and characteristically harbours a HEY1-NCOA2 gene fusion. A recent study has shown that NKX3.1 immunohistochemistry (IHC) is highly specific and sensitive in MCs. NKX3.1 is a nuclear marker expressed in prostatic tissue and is widely used in most laboratories to determine prostatic origin of metastatic tumours. In the current study we investigated whether this stain can be used in the diagnostic workup of MC, as it may assist in triaging cases for further molecular testing, by assessing its expression in a cohort of MCs and in a wide spectrum of sarcoma types. Furthermore, we aimed to elucidate if expression of NKX3.1 by MCs is related to androgen receptor (AR) expression. We identified NKX3.1 positive nuclear staining in 9 of 12 individual patients of MC (n=20 of 25 samples when taking into account separate episodes). Four of the five negative specimens had been previously subjected to acid-based decalcification. NKX3.1 was negative in 536 samples from 16 non-MC sarcomas derived from largely tissue microarrays (TMAs). Overall, we identified 80% sensitivity and 100% specificity for NKX3.1 IHC in MCs. The sensitivity increased to 95.2% when acid-based decalcified specimens were excluded from the analysis. No correlation between NKX3.1 expression and AR IHC was identified. In summary, our findings indicate that NKX3.1 nuclear positivity is highly sensitive and specific for MC, provided that ethylenediaminetetraacetic acid (EDTA)-based rather than acid-based decalcification is used for sample processing. NKX3.1 IHC in the right clinical and histopathological setting can potentially be sufficient for the diagnosis of MC, reserving molecular confirmation only for equivocal cases.

Genome wide methylation profiling of selected matched soft tissue sarcomas identifies methylation changes in metastatic and recurrent disease.

In this study we used the Illumina Infinium Methylation array to investigate in a cohort of matched archival human tissue samples (n = 32) from 14 individuals with soft tissue sarcomas if genome-wide methylation changes occur during metastatic and recurrent (Met/Rec) disease. A range of sarcoma types were selected for this study: leiomyosarcoma (LMS), myxofibrosarcoma (MFS), rhabdomyosarcoma (RMS) and synovial sarcoma (SS). We identified differential methylation in all Met/Rec matched samples, demonstrating that epigenomic differences develop during the clonal evolution of sarcomas. Differentially methylated regions and genes were detected, not been previously implicated in sarcoma progression, including at PTPRN2 and DAXX in LMS, WT1-AS and TNXB in SS, VENTX and NTRK3 in pleomorphic RMS and MEST and the C14MC / miR-379/miR-656 in MFS. Our overall findings indicate the presence of objective epigenetic differences across primary and Met/Rec human tissue samples not previously reported.

DNA damage-inducible transcript 3 immunohistochemistry is highly sensitive for the diagnosis of myxoid liposarcoma but care is required in interpreting the significance of focal expression.

AIMS: Myxoid liposarcoma (MLPS) is characterised by DNA damage-inducible transcript 3 (DDIT3) gene rearrangements, confirmation of which is commonly used diagnostically. Recently, DDIT3 immunohistochemistry (IHC) has been reported to be highly sensitive and, when strict criteria are employed, specific for the diagnosis of MLPS. The aim of this study was to independently investigate DDIT3 IHC as a diagnostic marker for MLPS. METHODS AND RESULTS: DDIT3 IHC was performed on 52 MLPS and on 152 mimics on whole sections, and on 515 non-MLPS sarcomas in tissue microarray format. Only one MLPS (which had undergone acid-based decalcification) was completely negative. With inclusion of this case if any nuclear expression is considered to indicate positivity, the overall sensitivity of DDIT3 is 98% (51 of 52 cases) and the specificity is 94% (633 of 667 non-MLPS cases are negative). If a cut-off of >10% of neoplastic cells is required for positivity, then the sensitivity remains 98% (51/52) and the specificity is 98.5% (657 of 667 non-MLPS cases are negative). If a cut-off of >50% of cells is required for positivity, then the sensitivity is 96% (50 of 52 cases) but the specificity improves to 100%. CONCLUSIONS: Diffuse nuclear DDIT3 expression occurs in the overwhelming majority of MLPSs, and can be used to confirm the diagnosis in most cases without the need for molecular testing. A complete absence of expression argues strongly against MLPS, and almost completely excludes this diagnosis, particularly if there is consideration of technical factors such as decalcification. The significance of focal DDIT3 expression should be interpreted in the morphological and clinical context, although most tumours showing only focal expression are not MLPS.

PD-1 blockade using pembrolizumab in adolescent and young adult patients with advanced bone and soft tissue sarcoma.

BACKGROUND: Sarcomas represent 10%-15% of cancers in adolescent and young adult (AYA) patients, and survival for those with metastatic disease or relapse is poor. Immunotherapy with checkpoint inhibition has improved outcomes in multiple tumor types, but data in advanced sarcomas, particularly within the AYA population, are limited. AIM: We aim to evaluate response and toxicity for AYA patients with sarcoma treated with pembrolizumab. METHODS AND RESULTS: We retrospectively reviewed AYA patients with advanced bone and soft tissue sarcoma who received self-funded pembrolizumab between May 2015 and January 2019. Eighteen patients were identified. One patient with Ewing sarcoma had a sustained complete response to therapy. Two patients with alveolar soft part sarcoma received a clinical benefit from pembrolizumab: one had a radiological partial response with an excellent clinical response and one patient achieved stable disease. Four patients died of disease prior to first scheduled assessment and thus were not evaluable. The remaining eleven patients had progressive disease. CONCLUSION: The role of immunotherapy in AYA sarcoma warrants further investigation. Biomarkers of response need to be further evaluated in order to guide patient selection.

Glossary of terms for musculoskeletal radiology.

Members of the International Skeletal Society compiled a glossary of terms for musculoskeletal radiology. The authors also represent national radiology or pathology societies in Asia, Australia, Europe, and the USA. We provide brief descriptions of musculoskeletal structures, disease processes, and syndromes and address their imaging features. Given the abundance of musculoskeletal disorders and derangements, we chose to omit most terms relating to neoplasm, spine, intervention, and pediatrics. Consensus agreement was obtained from 19 musculoskeletal radiology societies worldwide.

Prevalence of PD-L1 expression in matched recurrent and/or metastatic sarcoma samples and in a range of selected sarcomas subtypes.

We assessed the frequency of programmed death-ligand 1 (PD-L1) expression by immunohistochemistry (IHC) in a cohort of 522 sarcomas from 457 patients, incuding a subset of 46 patients with 63 matched samples from local recurrence or metastases with primary tumours and/or metachronous metastases. We also investigated the correlation of PD-L1 with the presence and degree of tumour-infiltrating lymphocytes (TILs) in a subset of cases. IHC was performed using the PD-L1 SP263 companion kit (VENTANA) on tissue microarrays from an archival cohort. Evaluation of PD-L1 and TILs was performed on full sections for a subset of 23 cases. Fisher's exact and Mann Whitney test were used to establish significance (P <0.05). PD-L1 positive expression (≥1%) was identified in 31% of undifferentiated pleomorphic sarcomas, 29% of angiosarcomas, 26% of rhabdomyosarcomas, 18% of myxofibrosarcomas, 11% of leiomyosarcomas and 10% of dedifferentiated liposarcomas. Negative expression was present in all atypical lipomatous tumous/well-differentiated lipoasarcomas, myxoid liposarcomas, synovial sarcomas, pleomorphic liposarcomas, and Ewing sarcomas. PD-L1 IHC was concordant in 81% (38 of 47) of matched/paired samples. PD-L1 IHC was discordant in 19% (9 of 47 matched/paired samples), displaying differences in the proportion of cells expressing PD-L1 amongst paired samples with the percentage of PD-L1-positive cells increasing in the metastatic/recurrent site compared to the primary in 6 of 9 cases (67%). Significant correlation between PD-L1 expression and the degree of TILs was exclusively identified in the general cohort of leiomyosarcomas, but not in other sarcoma subtypes or in metastatic/recurrent samples. We conclude that the prevalence of PD-L1 expression in selected sarcomas is variable and likely to be clone dependent. Importantly, we demonstrated that PD-L1 can objectively increase in a small proportion of metastases/recurrent sarcomas, offering the potential of treatment benefit to immune checkpoint inhibitors in this metastatic setting.

NTRK-rearranged mesenchymal tumours: diagnostic challenges, morphological patterns and proposed testing algorithm.

Oncogenic fusions involving neurotrophic receptor tyrosine kinase (NTRK) genes are being increasingly identified in a range of mesenchymal tumours unrelated to infantile fibrosarcoma or cellular congenital mesoblastic nephroma, where the canonical ETV6-NTRK3 fusion was first described more than two decades ago. Recognition of these NTRK-rearranged tumours poses a diagnostic challenge to surgical pathologists due to their non-specific clinical and pathological features. However, their recognition is of heightened importance, particularly in locally advanced and metastatic sarcomas, due to the recent availability of selective and highly effective targeted therapy. Herein, we present an Australian multi-institutional series of six of these rare NTRK-rearranged mesenchymal neoplasms to share the local experience and diagnostic challenges as well as to highlight key morphological patterns and immunoprofiles that provide the most helpful clues in routine practice. We also propose a diagnostic algorithm for the detection of these fusions, drawing attention to the limitations of ancillary studies including immunohistochemistry against tropomyosin receptor kinase (TRK) protein, fluorescence in situ hybridisation (FISH) and next generation sequencing.