Surgical resection and targeted therapy in a pediatric NTRK-rearranged low-grade spindle cell sarcoma: a case report.

Neurotrophic tropomyosin receptor kinase (NTRK) gene fusion has been identified as an oncogenic driver of various solid tumors, and it is rare in non-smalll cell lung cancer (NSCLC) with a frequency of approximately less than 1%. Next-generation sequencing (NGS) is of priority for detecting NTRK fusions, especially RNA-based NGS. Currently, the tropomyosin receptor kinase (TRK) inhibitors have shown promising efficacy and well tolerance in patients with NTRK fusion-positive solid tumors, regardless of tumor histology. The first-generation TRK inhibitors (larotrectinib and entrectinib) are recommended as the first-line treatment for locally advanced or metastatic NSCLC patients with positive NTRK fusion. However, TRK inhibitor resistance can eventually occur due to on-target or off-target mechanisms. Further studies are under investigation to overcome resistance and improve survival. Interestingly, NTRK fusion might be the mechanism of resistance to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKI) in NSCLC patients with EGFR mutation. Regarding immunotherapy, the efficacy of immune checkpoint inhibitors in NSCLC patients harboring NTRK fusion has yet to be well described. In this review, we elucidate the function of NTRK genes, summarize the diagnostic techniques for NTRK fusions, and present clinical data for TRK inhibitors; we also discuss potential mechanisms of resistance to TRK inhibitors.

Spotlight on the treatment of infantile fibrosarcoma in the era of neurotrophic tropomyosin receptor kinase inhibitors: International consensus and remaining controversies

Neurotrophic tropomyosin receptor kinase (NTRK)-rearranged spindle cell tumors are often resistant to chemotherapy and radiotherapy. Fortunately, they are sensitive to targeted therapy of tropomyosin receptor kinase (TRK) inhibitors. However, the data on larotrectinib in Chinese children with NTRK-rearranged spindle cell tumor are still scarce. We reported 4 children with TRK fusion-positive solid tumors received larotrectinib in different clinical scenarios, including second-line treatment after progressive disease (patient #1), relapse after resection (patients #2 and #3), and metastatic disease (patient #4) and all of them benefited from the treatment. The patients harbored different TRK fusion genes (patient #1: TP53-NTRK1; #2: TPM3-NTRK1; #3: TPM3-NTRK1, DCST1-NTRK1, ZBTB7B-NTRK1, and NTRK1-DCST2; #4: LMNA-NTRK1). Our study provides new insights into the biology and management of NTRK-rearranged spindle cell tumors, contributing to the expanding evidence supporting the use of TRK inhibitors in these tumors. Further studies are needed to validate our findings and to explore the potential of second-generation TRK inhibitors in overcoming resistance.

Precision medicine aims to identify the genetic landscapes of each patient's cancer to maximize effectiveness and minimize toxicity to normal cells. Due to the efficacy of tropomyosin receptor kinase (TRK) inhibitor therapy, it is currently clinically recommended to identify patients with neurotrophic tropomyosin receptor kinase (NTRK) fusion-driven cancer. In this article we aim to provide perceptions to enhance best clinical practices about NTRK gene fusion testing and monitoring parameters for the approved TRK inhibitors as well as its comparative effectiveness based on previously published articles and guidelines. Identification of NTRK gene fusion may be attained using different methods based on histology and molecular findings. The possible methods for detection are immunohistochemistry, fluorescence in situ hybridization, reverse transcriptase polymerase chain reaction and next generation sequencing. FDA approved two TRK inhibitors Larotrectinib and Entrectinib. Based on management guidelines, oncologists have one opportunity to decide which TRK inhibitor to choose for patients. There is no direct comparison in clinical trials and Larotrectinib versus Entrectinib comparative efficacy still unclear. In addition, cross-trial comparisons are susceptible to potential biases. Indirect comparative efficacy of Larotrectinib (Vitrakvi) versus Entrectinib (Rozlytrek) was conducted by Jesus Garcia-Foncillas and colleagues. The matching-adjusted indirect comparison (MAIC) to compare the 2 agents was utilized. They assumed this model would aid to balance baseline characteristics and facilitate cross-trial comparisons. The published findings propose favorable efficacy for Larotrectinib in regard to OS and PFS and comparable ORR and safety profiles compared to Entrectinib in treating TRK fusion positive cancer. In conclusion, further research should re-assess the comparative effectiveness of both TRK inhibitors as long-term survival data mature and increased number of patients are treated. Furthermore, data with longer follow up times will further enlighten this comparison.

e15537 Background: Inhibitors of tropomyosin receptor kinase (TRK) have shown promising activity against neurotrophic TRK ( NTRK) fusion-driven cancers, regardless of tumor histotype or cell of origin. NTRK gene fusions are observed in less than 1% of colorectal cancers (CRCs). CRCs harboring wild-type BRAF and KRAS and MisMatch Repair deficiency (dMMR)/MicroSatellite Instability (MSI) due to MLH1 hypermethylation have been associated with NTRK fusions in small cohorts of non-metastatic tumors. We aimed at evaluating the incidence of NTRK fusions among dMMR/MSI metastatic CRCs (mCRC) for which there is a need for innovative therapies, as well as the associated clinical characteristics of these patients (pts) carrying NTRK fusion-positive tumors. Methods: Tumor samples of dMMR/MSI mCRC pts, paired primary and metastasis or primary alone, were obtained from a French multicenter retrospective cohort and from a single-center cohort of patients treated by immune checkpoint inhibitors (ICI) (Saint-Antoine Hospital, Paris). Clinico-pathological data including KRAS and BRAFV600E status, MMR proteins and MLH1 methylation status were available for all pts. All samples were screened for TRK expression by immunohistochemistry (IHC) using a pan-TRK antibody (clone EPR17341, Abcam; positivity: 1% of labeled tumor cells)) and for NTRK1 and NTRK3 gene rearrangements, by fluorescent in situ hybridation (FISH). A threshold of 15% nuclei positive for a break apart signal was considered positive for gene rearrangement. Results: A total of 158 pts with dMMR/MSI mCRCs (paired samples: n=39; primary only: n=119) were screened. Tumor samples of 10 patients (6.3%) harbored NTRK fusion genes by FISH ( NTRK1=8; NTRK3=2). Only four of these 10 patients had TRK immunoreactivity. One patient showed a discordance between metastasis harboring NTRK1 fusion (+) and primary tumor being negative. Eight tumors were sporadic with MLH1 hypermethylation. The remaining 2 cases were related to a MMR gene germline mutation (Lynch syndrome) with concurrent loss of MSH2 and MSH6 expression and isolated loss of MSH6 respectively. One Lynch-related tumor was KRAS mutated, one sporadic MLH1-negative tumor was BRAF V600E mutated. Four patients out of 91 treated by ICI had tumors with NTRK fusions. Three have shown radiological response according to iRECIST criteria (two complete responses, one partial response with 25 to 54 months of follow up) and one had primary resistance to ICI. Conclusions: Frequency of NTRK1/3 fusions is 6.3% in our dMMR/MSI mCRCs population. These fusions are not restricted to sporadic cases. The diagnostic accuracy of pan-TRK IHC is low. Optimal testing algorithms for theragnostics remain to be defined in this setting.

There is sparse published information on computed tomographic (CT) characteristics of canine gastrointestinal tumors. The purposes of this multi-center, retrospective, descriptive study were to describe the CT features of histologically-confirmed canine gastrointestinal spindle cell, epithelial, and round cell tumorsand, when available, describe the corresponding ultrasound findings. The inclusion criteria were as follows: availability of pre-and post-contrast CT study, and a histopathological diagnosis of the lesions. Recorded parameters were tumor size, location, gastrointestinal wall layers involvement, lesion's growth and enhancement patterns, tumor margination, presence of stenosis, mineralization, ulcerations, lymphadenopathy, or other lesions in the abdomen/thorax. When available, ultrasound images were evaluated. Forty-one dogs met the inclusion criteria and had the following histological diagnoses: 21/41 (51%) spindle cells (7 leiomyomas, 14 leiomyosarcomas/gastrointestinal stromal tumors (GISTs)), 13/41 (32%) epithelial (adenocarcinoma), and 7/41 (17%) round cell (lymphoma) tumors. The growth pattern was concentric, eccentric, and mixed in epithelial, spindle cell, and round cell tumors, respectively. Spindle cell tumors had the largest main volume and involved the outer gastrointestinal layer with an unaffected inner layer. Leiomyosarcomas/GISTs showed irregular margins compared to leiomyomas. Only lymphomas showed multifocal gastrointestinal involvement. Nine carcinomas and six spindle cell tumors caused partial stenosis with secondary sub-obstruction. Mineralizations were more frequent in spindle cell tumors (10/21) and absent in lymphomas. Lymphadenomegaly was widespread in lymphomas, regional in leiomyosarcomas-GISTs and adenocarcinomas, and absent in leiomyomas. The reported CT features may be useful in prioritizing the differential diagnosis between spindle cell, epithelial, and round cell tumors, similar to those reported on ultrasound.

Neurotrophic tropomyosin receptor kinase (NTRK) gene fusions are rare in high-grade gliomas. The FDA approved the use of selective TRK inhibitors in 2018 for TRK fusion-positive cancers. However, clinical evidence in gliomas remain limited due to the rarity of these mutations. We present the clinical course of two adult patients with high grade glioma who were successfully treated with TRK inhibitors. Both patients presented with seizures and were found to have high grade glioma of the temporal lobe. NTRK2 fusion was detected via next-generation sequencing (NGS) testing. They underwent standard of care treatment including surgical resection and concurrent chemoradiation. TRK inhibitor therapy was added to conventional adjuvant chemotherapy in the adjuvant setting. Patients were evaluated monthly for clinical response and side effect profile, and magnetic resonance imaging of the brain was obtained every other month to ensure response. At the time of disease progression, these patients underwent surgical resection with NGS testing repeated on recurrent disease. Follow up NGS showed loss of NTRK2 fusion, suggesting successful treatment of the targeted NTRK fusion. This case series shows potential benefit of integrating TRK inhibitors with standard chemotherapy in NTRK fusion-positive high-grade gliomas. The evolution in NGS findings highlight the heterogeneous and evolving nature of tumor microenvironment and support obtaining serial molecular testing, when possible, to guide treatment planning. Further prospective studies are needed to validate these findings, evaluate long-term outcomes, and better understand the resistance mechanism in this patient population.

Background Fusions involving the neurotrophic tropomyosin receptor kinase (NTRK) gene family NTRK1, NTRK2, and NTRK3 lead to the expression of chimeric rearrangements in the TRK tyrosine kinase proteins (TRKA, TRKB, and TRKC, respectively) with constitutively active kinase function. NTRK fusions act as oncogenic drivers, and are potential therapeutic targets across a broad range of tumor types including breast cancer. Entrectinib is a CNS-active, oral, potent inhibitor of TRKA/B/C, ALK and ROS1 designed to cross the blood-brain-barrier. Here we present integrated efficacy data from three trials of entrectinib in NTRK fusion-positive solid tumors focusing on a small cohort of patients with breast cancer, and safety data from the integrated safety population. Methods Patients with locally advanced/metastatic NTRK fusion-positive tumors (with or without baseline CNS disease) confirmed by nucleic acid-based methods were enrolled in three global phase 1/2 entrectinib trials at >150 sites in 15 countries (ALKA-372-001 [EudraCT 2012-000148-88], STARTRK-1 [NCT02097810], STARTRK-2 [NCT02568267]). Disease burden was assessed per blinded independent central review (BICR) using RECIST v1.1 after cycle 1 (4 weeks) then every 8 weeks thereafter. The primary endpoints were objective response rate (ORR) and duration of response (DOR) by BICR. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and safety. Results The total efficacy-evaluable population comprised 54 adult patients with advanced/metastatic NTRK fusion-positive tumors; within this population 10 different tumor types and >19 histopathologies were identified. In the overall integrated analysis population, responses to treatment with entrectinib occurred in all tumor types and included 4 complete responses (7.4%). The ORR by BICR was 57.4% (95% CI 43.2-70.8), and median (95% CI) DOR, PFS, and OS were 10.4 (7.1-not estimable [NE]), 11.2 (8.0-14.9), and 20.9 (14.9-NE) months, respectively. In the cohort of 6 patients with NTRK fusion-positive breast cancer, the median age was 63 years (range 36-67 years). Three patients reported prior systemic therapies (6, 4 and 1 prior therapies). The majority of patients had an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1 (66.7%). Two patients had investigator-assessed CNS metastases at baseline; 1 patient (16.7%) had previously received radiotherapy in the brain 2-6 months prior to treatment with entrectinib. ORR by BICR was 83.3% (95% CI 35.9-99.6); 2 were complete responses, 3 were partial responses, and 1 patient had missing/unevaluable data. Median (95% CI) DOR, PFS, and OS were: 12.9 (4.2- NE), 10.1 (5.1-NE), and NE (5.1-NE) months, respectively. The integrated safety population comprised 355 patients who received ≥1 dose of entrectinib, of which 60.5% of patients had grade 1 or 2 treatment-related adverse events (TRAEs), 27.6% had grade 3, 3.4% had grade 4, and there were no grade 5 TRAEs. The most frequently reported TRAEs were dysgeusia (41.4%), fatigue (27.9%), dizziness (25.4%) and constipation (23.7%). TRAEs led to dose reductions in 27.3%, interruptions in 25.4% and discontinuations in 3.9% of patients. Conclusion In this integrated analysis of global multicenter clinical trials, entrectinib was well tolerated and induced clinically meaningful, durable responses in patients with NTRK fusion-positive breast cancer. Study Sponsor: Ignyta, Inc., a wholly owned subsidiary of F. Hoffmann-La Roche Ltd. Citation Format: Collin Blakely, Christophe Le Tourneau, Janice Lu, Saiama N. Waqar, Xinhui Huang, Bann-mo Day, Brian Simmons, Minal Barve. Entrectinib in NTRK fusion-positive breast cancer: Integrated analysis of patients enrolled in STARTRK-2, STARTRK-1 and ALKA-372-001 [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-10-11.

Low-grade fibromyxoid sarcomas are uncommon deep-seated soft tissue neoplasms that exhibit a deceptively benign appearance microscopically. The finding of a linear or whorled array of spindled cells with few or no mitoses in a characteristic myxoid stroma can pose diagnostic dilemmas. Recurrences are common, and late metastases have been recorded. A closely related tumor, the so-called hyalinizing spindle cell tumor with giant collagen rosettes (HSCTGR), has also been described, with both the neoplasms having a similar cytogenetic abnormality and clinical behavior. Because of the similarities, both lesions are considered to be a single entity within the spectrum of low-grade sarcomas. Two cases of HSCTGR occuring in the lower limb are described in this report.

Aberrant activation of tropomyosin receptor kinases (TRKs) is a well-defined oncogenic driver for neurotrophic tropomyosin receptor kinase (NTRK)-fusion cancers, and acquired resistant mutations have emerged with clinical use of the first-generation TRK inhibitors. Here we present BPI-28592, a novel second-generation TRK inhibitor with efficacy against TRK fusion-positive cancers, including those with resistant mutations. Docking simulations indicated no steric hindrance between BPI-28592 and TRK mutants, suggesting its potential to overcome drug resistance. Biochemical assays showed strong inhibition and high selectivity against TRKA, TRKB, and TRKC. The inhibitor significantly reduced cell proliferation and blocked TRK signaling. In vivo studies demonstrated effective tumor suppression in xenograft models harboring TRK fusions with or without resistant mutations. Clinically, BPI-28592 achieved a complete response in a patient with malignant melanoma carrying an AP3S2-NTRK3 fusion (Clinicaltrials. gov identifier: NCT05302843).

Spindle cell thymomas are the most common spindle cell neoplasms of the anterior mediastinum. These tumors belong to the group of thymic epithelial neoplasms and are known for their wide histomorphologic spectrum. This histological heterogeneity is the reason why unequivocal diagnosis can be challenging, especially when dealing with small biopsy material. Conversely, less conventional patterns of the tumor may also pose significant diagnostic problems in resected material and the differential diagnosis often includes other spindle cell neoplasms that are known to arise in the mediastinal cavity. These can be of variable origin and may share overlapping pathological features with spindle cell thymoma. Since spindle cell thymomas are tumors that primarily affect the adult population and predominantly arise from the thymic gland in the anterior mediastinum, this review will focus on the differential diagnosis with other spindle cell neoplasms that share similar demographic characteristics and, for the most part, originate from the anterior mediastinal compartment. These include other epithelial spindle cell tumors of thymic origin (sarcomatoid thymic carcinoma and spindle cell carcinoid tumor), mesenchymal neoplasms [solitary fibrous tumor (SFT), synovial sarcoma, and dedifferentiated liposarcoma] and various other tumors with spindle cell morphology, that may occasionally involve the anterior mediastinum. The clinical, pathological, immunohistochemical and molecular hallmarks of these lesions will be discussed and useful tips for the differential diagnosis with spindle cell thymoma will be provided.

Uterine sarcomas.

Cutaneous epithelioid and spindle cell neoplasms occasionally pose a significant diagnostic challenge on purely histologic grounds. Given the substantial clinicopathologic overlap between these lesions, especially in small biopsies, the use of immunohistochemical studies are essential. We evaluated the utility of a battery of immunohistochemical markers, including podoplanin (D2-40), CD10, p63, and wide-spectrum cytokeratin, for distinguishing cutaneous epithelioid and spindle cell tumors. A total of 81 cases, including 42 atypical fibroxanthoma (AFX), 13 spindle cell melanoma, 10 sarcomatoid carcinoma, 9 leiomyosarcoma (LMS), and 7 leiomyoma, formed the basis of our study. Immunohistochemical results were as follows-AFX: CD10 (35 of 42), p63 (1 of 42), CK (1 of 42), and podoplanin (19 of 42); spindle cell melanoma: CD10 (7 of 13), p63 (0 of 13), CK (0 of 13), and podoplanin (2 of 13); sarcomatoid carcinoma: CD10 (5 of 10), p63 (7 of 10), CK (4 of 10), and podoplanin (7 of 10); LMS: CD10 (4 of 9), p63 (0 of 9), CK (2 of 9), and podoplanin (1 of 9); and leiomyoma: CD10 (0 of 7), p63 (0 of 7), CK (0 of 7), and podoplanin (1 of 7). Our findings showed that the combination of certain immunohistochemical markers may be a useful adjunct in the evaluation of epithelioid and spindle cell tumors of the skin. In this study, we found that a combination of wide-spectrum cytokeratin and p63 are most helpful in the distinction of sarcomatoid carcinomas from other tumors; however, there remains a substantial minority of cases of sarcomatoid carcinoma that will consistently demonstrate negative staining for these markers. We also found that CD10 and podoplanin (D2-40) have limited diagnostic utility in epithelioid and spindle cell tumors of the skin; however, a strong and diffuse pattern of staining will favor the diagnosis of AFX. Caution should also be observed in the diagnosis of spindle cell malignant melanoma because some cases may express CD10, p63, and podoplanin while being nonreactive to S100 protein. Awareness of the limitations of the use of these stains and familiarity with their staining patterns in spindle and epithelioid cell tumors of the skin are extremely important because the prognostic and therapeutic implications for such neoplasms may be quite different.

A subset of low-grade fibrosarcomas is composed of CD34-positive spindle cells. These include dermatofibrosarcoma, its morphologic variants, and its associated fibrosarcoma, solitary fibrous tumor, hemangiopericytoma and their malignant counterparts, and some cases of myxoinflammatory fibroblastic sarcoma. Dermatofibrosarcoma and related lesions are characterized by a t(17;22)(q22;q13) rearrangement resulting in fusion of the genes COL1A (17q21-22) and PDGFB1 (22q13). Solitary fibrous tumor displays varying cellularity and fibrosis and a peripheral hemangiopericytomatous pattern; most tumors formerly called hemangiopericytoma are now subsumed into the category of solitary fibrous tumor, although a few strictly defined examples are recognized; however, these are probably not composed of pericytes. Myofibroblastic malignancies are best identified by electron microscopy, with which varying degrees of differentiation, including the presence of fibronexus junctions, can be identified. Low-grade sarcomas showing myofibroblastic differentiation include myofibrosarcomas and inflammatory myofibroblastic tumors. Myofibrosarcomas are spindle cell neoplasms that occur in children or adults in the head and neck, trunk, and extremities as infiltrative neoplasms and that display a fascicular or fasciitis-like pattern with focal nuclear atypia and variable expression of myoid antigens. These sarcomas are prone to recurrence and a small number metastasize. Inflammatory myofibroblastic tumor (synonymous with inflammatory fibrosarcoma) is a neoplasm arising predominantly in childhood, and frequently in intraabdominal locations. It has spindle cells in fascicular, fasciitis-like and sclerosing patterns, with heavy chronic inflammation including abundant plasma cells. Many IMT have clonal chromosomal abnormalities involving 2p22-24, and fusion of the ALK gene with tropomyosin 3 (TPM3-ALK) or tropomyosin 4 (TPM4-ALK) is found in a subset.

Background NTRK gene fusions have been identified in various tumors; some requiring aggressive therapy and sometimes new TRK inhibitors (TRKi). We aimed to describe a national, unselected, retrospective, multicenter cohort. Research design and methods Patients were identified through the French sarcoma diagnostic laboratory at Institut Curie through samples analyzed by RT-qPCR or whole-transcriptome sequencing. Results From 2001 to 2019, 65 NTRK fusion tumors were identified within 2120 analyses (3.1%): 58 by RNA sequencing (including 20 after RT-qPCR analysis) and 7 exclusively by RT-qPCR. Of the 61 patients identified, 37 patients had infantile soft tissue or kidney fibrosarcomas (IFS), 15 other mesenchymal (Other-MT) and nine central nervous system (CNS) tumors. They encompassed 14 different tumor types with variable behaviors. Overall, 53 patients had surgery (3 mutilating), 38 chemotherapy (20 alkylating agents/anthracycline), 11 radiotherapy, two ‘observation strategy’ and 13 received TRKi. After a median follow-up of 61.0 months [range, 2.5–226.0], 10 patients died. Five-year overall survival is, respectively, 91.9% [95%CI, 83.5–100.0], 61.1% [95%CI, 34.2–100.0] and 64.8% [95%CI, 39.3–100.0] for IFS, Other-MT, and CNS groups. Conclusions NTRK-fusion positive tumors are rare but detection is improved through RNA sequencing. TRKi could be considered at diagnosis for CNS NTRK-fusion positive tumors, some IFS, and Other-MT. Trial Registration Not adapted.