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Lymphangiomyomatosis is a member of the PEComa family, and usually involves the pulmonary parenchyma of middle-aged females. Infrequently, it may involve abdominal and retroperitoneal lymph nodes, and rarely it has been described to be associated with fallopian tube-type ciliated epithelium co-existing in one neoplasm. To increase our understanding of this unusual tumor, we describe the morphology and genetics of one case and review the literature. We present the case of a 50-year-old female found to have 12.5 and 7.7 cm cystic retroperitoneal masses, describe its unique pathological features and review the literature on the previously reported cases. Based on its unique morphological, immunohistochemical, and molecular features we propose the term adenoPEComa to represent this entity. This case represents a rare example of adenoPEComa with lymphangiomyomatosis of the lymph nodes. It is the first example that has undergone next-generation sequencing revealing a mutation in TSC2 making it a confirmed member of the PEComa family of tumors.

Supplementary Data from Systemic Chemotherapies Retain Antitumor Activity in Desmoid Tumors Independent of Specific Mutations in CTNNB1 or APC: A Multi-institutional Retrospective Study

Purpose:Determine whether specific CTNNB1 or APC mutations in patients with desmoid tumor were associated with differences in clinical responses to systemic treatments.Experimental Design:We established a multi-institutional dataset of previously treated patients with desmoid tumor across four U.S. sarcoma centers, including demographic and clinicopathologic characteristics, treatment regimens, and clinical and radiographic responses. CTNNB1 or APC mutation status was determined from prior pathology records, or archival tissue was requested and analyzed by Sanger sequencing and/or next-generation sequencing. Evaluable patients with mutation results were analyzed to determine clinical progression-free survival (cPFS), RECIST 1.1 PFS (rPFS), time to next treatment (TTNT), and overall survival (OS). Kaplan–Meier analysis and Cox proportional hazards regression were performed to identify differences in cPFS, rPFS, TTNT, and OS by mutation subtype, desmoid tumor location, and treatment regimen.Results:A total of 259 evaluable patients were analyzed for at least one of the survival outcomes, with 177 patients having mutation data. First- and second-line cPFS, rPFS, and TTNT were not significantly affected by mutation subtype; however, APC-mutant desmoid tumors demonstrated nonstatistically significant inferior outcomes. Extremity/trunk desmoid tumor location and treatment with doxorubicin-based, methotrexate/vinca alkaloids and sorafenib regimens were associated with better clinical outcomes compared with surgery or “other” therapies, including estrogen-receptor blockade and imatinib. OS was significantly worse with APC or CTNNB1 negative/other mutations.Conclusions:Mutation subtype did not affect responses to specific systemic therapies. APC mutations and nonextremity desmoid tumor locations remain prognostic for worse outcomes, and earlier initiation of systemic therapy for these higher-risk desmoid tumors should be prospectively evaluated.See related commentary by Greene and Van Tine, p. 3911

Supplementary Figure from Systemic Chemotherapies Retain Antitumor Activity in Desmoid Tumors Independent of Specific Mutations in CTNNB1 or APC: A Multi-institutional Retrospective Study

Does racial discrimination persist in global mobility rights? While many states explicitly discriminated based on race far into the twentieth century, contemporary migration policymaking is now putatively objective. The rise of white supremacist violence against all varieties of migrants, politician statements, and public support for restrictive policies calls this supposed color blindness into question. However, existing work is not discerning because most policies appear objective. In this article, I use new data on bilateral visa waiver policies from 1973 to 2013 to show that racial difference predicts whether a country receives a visa waiver, even after accounting for its economic, political, and security context. This conditional racial discrimination has worsened since 9/11. In so doing, I provide evidence of systematic racial discrimination in international visa policymaking. The results have important implications for the study of racial inequality in the international system.

Purpose: Determine whether specific CTNNB1 or APC mutations in patients with desmoid tumor were associated with differences in clinical responses to systemic treatments. Experimental Design: We established a multi-institutional dataset of previously treated patients with desmoid tumor across four U.S. sarcoma centers, including demographic and clinicopathologic characteristics, treatment regimens, and clinical and radiographic responses. CTNNB1 or APC mutation status was determined from prior pathology records, or archival tissue was requested and analyzed by Sanger sequencing and/or next-generation sequencing. Evaluable patients with mutation results were analyzed to determine clinical progression-free survival (cPFS), RECIST 1.1 PFS (rPFS), time to next treatment (TTNT), and overall survival (OS). Kaplan–Meier analysis and Cox proportional hazards regression were performed to identify differences in cPFS, rPFS, TTNT, and OS by mutation subtype, desmoid tumor location, and treatment regimen. Results: A total of 259 evaluable patients were analyzed for at least one of the survival outcomes, with 177 patients having mutation data. First- and second-line cPFS, rPFS, and TTNT were not significantly affected by mutation subtype; however, APC-mutant desmoid tumors demonstrated nonstatistically significant inferior outcomes. Extremity/trunk desmoid tumor location and treatment with doxorubicin-based, methotrexate/vinca alkaloids and sorafenib regimens were associated with better clinical outcomes compared with surgery or “other” therapies, including estrogen-receptor blockade and imatinib. OS was significantly worse with APC or CTNNB1 negative/other mutations. Conclusions: Mutation subtype did not affect responses to specific systemic therapies. APC mutations and nonextremity desmoid tumor locations remain prognostic for worse outcomes, and earlier initiation of systemic therapy for these higher-risk desmoid tumors should be prospectively evaluated. See related commentary by Greene and Van Tine, p. 3911

Primary malignant bone tumors are uncommon and their accurate classification requires careful correlation of clinical, radiological, and pathologic findings. It is a heterogeneous group of tumors with a wide spectrum of morphology and their biological potential can be of low- or high-grade, depending on their risk for developing metastases. Over the past several decades, the classification of bone sarcomas has remained largely constant. However, some of the tumors have been reclassified and several new entities have emerged. In this review, we will focus on pleomorphic fibrosarcoma/UPS and dedifferentiated bone tumors, discuss their key diagnostic features, differential diagnosis, and their relation to prognosis.

A focal adenomatoid-microcystic pattern is not uncommon in peritoneal mesothelioma, but tumors composed almost exclusively of this pattern are distinctly rare and have not been well characterized. A small subset of mesotheliomas (mostly in children and young adults) are characterized by gene fusions including EWSR1/FUS::ATF1, EWSR1::YY1, and NTRK and ALK rearrangements, and often have epithelioid morphology. Herein, we describe five peritoneal mesothelial neoplasms (identified via molecular screening of seven histologically similar tumors) that are pure adenomatoid/microcystic in morphology and unified by the presence of an NR4A3 fusion. Patients were three males and two females aged 31-70 years (median, 40 years). Three presented with multifocal/diffuse and two with a localized disease. The size of the individual lesions ranged from 1.5 to 8 cm (median, 4.7). The unifocal lesions originated in the small bowel mesentery and the mesosigmoid. Treatment included surgery, either alone (three) or combined with hyperthermic intraperitoneal chemotherapy (two), and neoadjuvant or adjuvant chemotherapy (one case each). At the last follow-up (6-13 months), all five patients were alive and disease-free. All tumors were morphologically similar, characterized by extensive sieve-like microcystic growth with bland-looking flattened cells lining variably sized microcystic spaces and lacked a conventional epithelioid or sarcomatoid component. Immunohistochemistry confirmed mesothelial differentiation, but most cases showed limited expression of D2-40 and calretinin. Targeted RNA sequencing revealed an NR4A3 fusion (fusion partners were EWSR1 in three cases and CITED2 and NIPBL in one case each). The nosology and behavior of this morphomolecularly defined novel peritoneal mesothelial neoplasm of uncertain biological potential and its distinction from adenomatoid variants of conventional mesothelioma merit further delineation as more cases become recognized.

In the last decade, new tumor entities have been described, including

An “unplanned excision” refers to soft tissue sarcomas excised without planning imaging studies and a diagnostic biopsy, resulting in the presence of residual disease and usually necessitating a re-excision procedure. We aimed to assess the impact of previous unplanned excisions on the intra-operative pathologic assessment at the time of re-excision, in terms of need to perform repeat assessments and the accuracy to predict margin status of the final pathologic specimen. Data was collected for all patients with extremity soft tissue sarcoma who had undergone wide local excision limb salvage surgery or amputation between 2012 and 2017. Intra-operative pathologic assessment with frozen sections was performed in all cases and was classified as negative, negative but close (

Salivary gland neoplasms are uncommon, and most exhibit epithelial differentiation. Mesenchymal neoplasms of the salivary gland are rare, and the incidence ranges from 1.9% to 5%. The aim of this study is to identify the types and clinical-pathological features of mesenchymal salivary neoplasm and review their differential diagnosis. A retrospective search for mesenchymal neoplasms of salivary glands from our institution's pathology archives from the 2004–2021 period and consultation files of one of the authors (AER) was performed. The clinical data were obtained from available medical records, and the histological slides and ancillary studies were retrieved and reviewed. We identified a total of 68 cases that form the study cohort. Thirty-five patients were male, and thirty-three patients were female, with a mean age of 48 years (range, 7 months–79 years), and the male to female ratio was 1:.94. Sixty-three (92.6%) of sixty-eight tumors were benign and included: 38 (56%) lipomas, 9 (13%) hemangiomas, 7 (10.3%) schwannomas, 3 (4.4%) neurofibromas, 3 (4.4%) lymphangioma, 2 (3%) solitary fibrous tumors, 1 (1.5%) myofibroma. Five of sixty-eight (7.4%) were malignant and included: 3 (4.4%) Adamantinoma-like Ewing sarcomas, 1 (1.5%) malignant peripheral nerve sheath tumor (MPNST), and 1 (1.5%) malignant solitary fibrous tumor. The involved sites included: parotid (55), submandibular gland (5), parapharyngeal space (5), buccal mucosa minor salivary gland (2), and sublingual gland (1). Sixty-seven patients underwent surgical resection. One patient with lymphangioma manifested a recurrence/persistence a week post-surgery. One patient with a parotid hemangioma developed post-operative numbness, and another patient developed chronic postauricular pain after surgery. Two patients with MPNST and one patient with adamantinoma-like Ewing sarcoma underwent neoadjuvant chemoradiation and were disease-free after treatment. The remaining 37 patients with available follow-up ranging from 7 days to 96 months (mean, 18 months) had a favorable outcome and were disease-free after treatment. Mesenchymal neoplasms of salivary gland are rare; most are benign and demonstrate adipocytic, endothelial, and schwannian differentiation; awareness of their development is important for adequate diagnosis. The mainstay of treatment is surgical excision, with the extent determined by tumor type. Adjuvant therapy is reserved for high-grade sarcomas and may be given in a neoadjuvant or adjuvant setting.

Rhabdomyosarcoma (RMS) encompasses a heterogeneous group of tumors with striated muscle differentiation. RMSs are classified as alveolar, embryonal, spindle cell /sclerosing and pleomorphic types and molecular analysis of these tumors has identified aberrations that are useful in their further subclassification. Spindle cell rhabdomyosarcoma (SpRMS) is uncommon and has been described with VGLL2 fusions, EWSR1/FUS-TFCP2 rearrangements, and myoD1 mutations - the mutations are associated with significantly different prognoses. Also, the NCOA2-MEIS1 fusion gene was recently described in two primary intraosseous RMS that contained spindle cell components. Herein, we report three cases of SpRMS harboring different novel fusion genes, one possessing EP300-VGLL3, a second with NCOA2-MEIS1 and CAV1-MET, and the third case had HMGA2-NEGR1 and multiple amplified genes. This article is protected by copyright. All rights reserved.

Aims Simple bone cysts are benign intramedullary tumours primarily involving the long bones in skeletally immature individuals. Several mechanisms have been proposed for their pathogenesis. Although the diagnosis is typically straightforward, the interpretation can be problematic, because of superimposed fracture causing them to resemble aneurysmal bone cysts and other tumours. EWSR1-NFATC2 or FUS-NFATC2 fusions, which are characteristic of a subset of aggressive round cell sarcomas, have been recently detected in simple bone cysts. The aim of this study was to examine the clinicopathological and molecular features in a series of simple bone cysts. Methods and results Using RNA-based next-generation sequencing and/or fluorescence in-situ hybridisation, we investigated the presence of EWSR1 or FUS rearrangements in nine simple bone cysts. The patients were five females and four males, aged 3-23 years (median, 14 years); the tumours ranged from 19 mm to 160 mm (median, 46 mm) in size, and involved the femur (n = 3), humerus (n = 2), fibula (n = 2), tibia (n = 1), and iliac wing (n =1). We identified three cases with EWSR1-NFATC2 fusion (showing identical breakpoints to those in EWSR1-NFATC2 sarcomas) and one additional case with FUS rearrangement. Unlike in EWSR1-NFATC2 sarcomas, immunohistochemical expression of NKX3.1 and NKX2.2 was absent in two simple bone cysts tested. Conclusions More than 40% of simple bone cysts harbour genetic alterations confirming that they are neoplastic, investigation of EWSR1 and/or FUS rearrangement may help to distinguish simple bone cysts from mimics, and NFATC2 rearrangement is not pathognomonic of malignancy.

Primary sarcomas of the larynx are rare and are associated with diagnostic and treatment challenges. Studies of these tumors are limited, and most examples have been reported as small series. To further increase our understanding of laryngeal sarcomas, we reviewed our experience of an adult cohort. A retrospective search for laryngeal sarcomas from our pathology archives and consultation files of one of the authors was performed. We studied 27 primary laryngeal sarcomas that included 25 males, and 2 females, with a mean age of 60 years (range 33–85). The cases included conventional chondrosarcoma (16), well-differentiated liposarcoma (2), clear cell chondrosarcoma (1), leiomyosarcoma (2), high grade myxofibrosarcoma (2), high grade myofibroblastic sarcoma (1), low-grade myofibroblastic sarcoma (1), malignant granular cell tumor (1), and Kaposi sarcoma (1). Data on treatment and follow-up was available in 17 and 16 cases, respectively. 12 patients underwent partial laryngeal resection; five had total laryngectomy, and the patient with Kaposi sarcoma received combined highly active antiretroviral therapy and chemotherapy. Three patients developed local recurrence, and two patients developed metastases. The remaining patients with follow up had a favorable outcome and were disease-free after treatment. The important differential diagnosis of spindle cell sarcoma is sarcomatoid squamous cell carcinoma, and their distinction often requires extensive sampling of the mucosal surface and immunohistochemical analysis. The mainstay of treatment for laryngeal sarcomas is surgical removal, with the extent dictated by tumor type and grade. Adjuvant therapy is reserved for high-grade sarcomas and may be given in a neoadjuvant or adjuvant setting.

Inflammatory myofibroblastic tumors (IMT) are spindle cell neoplasms with myofibroblastic differentiation and inflammatory infiltration that are typically benign in presentation but can present aggressively in rare circumstances. We herein report the case of a 17-year-old Jamaican female with metastatic IMT who initially presented to the emergency department in her hometown of Kingston, Jamaica with severe chest tightness. Due to severe hemoptysis in the emergency department, the patient underwent emergent right upper and middle lobectomy after initial radiological work-up showing a mixed density mass within the right upper lobe. Initial pathology done by a general pathologist interpreted immunohistochemical findings to be suggestive of histiocytic sarcoma. However, follow-up analysis by a sarcoma-specialized pathologist at our institution resulted in an interpretation of inflammatory myofibroblastic tumor. While typical treatment consists of surgical removal and chemotherapy, the aggressive presentation of this patient’s disease necessitated combinations of targeted therapies such as ALK inhibitors with immunotherapy

Objectives Epithelioid sarcoma (ES) rarely arises in the nerve. To increase our understanding of this unusual tumor originating in the nerve, we describe the features of three cases and review the literature. Methods Clinical data, imaging, pathology, treatment, and follow-up are detailed. A systematic literature review was conducted. Results Two patients were male and one female; the median age was 24 years. The patients had neurologic symptoms, and the tumors arose in large nerves and ranged from 2.4 to 5.8 cm. The tumors were avid on positron emission tomography–computed tomography and showed increased signal intensity on T2-weighted magnetic resonance imaging. Centered in the nerve, the tumors grew with an infiltrative pattern and encased the nerve fascicles. All were treated with wide resection, and adjuvant treatment included combinations of chemotherapy and radiation. One recurred, and the limb was amputated. Metastases were documented to lymph nodes, lung, pleura, and skin. One patient died of disease after 54 months. Literature review including our cases showed that tumors stained with pancytokeratin (9/9), EMA (4/4), and CD34 (7/7); there was loss of INI1 in all six cases tested. Conclusions ES rarely arises in the peripheral nerve, and its infiltrative nature often requires morbid surgery. The differential includes a variety of benign and malignant epithelioid neoplasms.

Background Pseudocarcinomatous squamous hyperplasia (PSH) within the bone is uncommon and closely mimics well-differentiated squamous cell carcinoma (SCC). It arises from cutaneous or mucosal surfaces and grows directly into the bone. This study analyzes a large series of PSH and discusses the clinicopathologic features that facilitate its distinction from SCC. Design Cases were identified from the surgical pathology files between 1985 and 2020. Results The 31 cases included 21 males, 9 females, 1 unknown sex; who were 20 to 87 years old (average: 59 y). Sites included mandible-17, maxilla-5, toes-4, and 1 case from finger, femur, tibia, ischium, and unknown. Fourteen patients had a history of SCC, 13 treated with resection and chemoradiation and developed infected osteoradionecrosis, 4-medication-related osteonecrosis, 3-peripheral vascular disease, and diabetes mellitus, 3-trauma, 3-osteomyelitis, 3-unknown, and 1-hematologic malignancy. All cases exhibited severe osteomyelitis and nests of reactive keratinizing squamous epithelium that matured towards the bone surface, lacked significant atypia, or mitotic activity but permeated the medullary cavity. Patients with previous SCC developed PSH after 2 months to 8 years (average: 4 y). Nineteen of 30 patients had follow-up (2 to 48 mo, average: 17 mo); 6 patients experienced repeated debridements over 2 months to 1 year; no patient developed SCC. Conclusions PSH involving bone is infrequent, complicates severe osteomyelitis, and is often therapy related. The clinical findings are usually not concerning for malignancy, however, the histologic findings are an important diagnostic pitfall because they mimic SCC.

Giant cell tumor of bone is a locally aggressive, rarely metastasizing neoplasm. Evidence suggests that the neoplastic cells may be osteoblastic in differentiation. Standard treatment is surgical removal, but medical therapy with denosumab, an inhibitor of receptor activator of nuclear factor-κβ ligand, has become a component of patient management in select cases. Denosumab-treated giant cell tumor of bone (DT-GCTB) shows drastic morphologic changes including the presence of abundant bone. To further determine the relationship of the neoplastic cells to osteoblast phenotype, we performed a morphologic and immunohistochemical study on a series of DT-GCTB. Cases of DT-GCTB were retrieved from surgical pathology files, available slides were reviewed, and immunohistochemistry for H3.3 G34W, SATB2, and p63 was performed. The cohort included 31 tumors from 30 patients (2:3 male:female), ages 15 to 73 years (median=36 y). The morphology of post-denosumab-treated tumors ranged from tumors composed of an abundant bone matrix with few spindle cells to spindle cell-predominant tumors. Five had focal residual classic CGTB, and 2 manifested mild nuclear atypia. The majority expressed all markers: 86.2% for H3.3 G34W, 96.7% for SATB2, and 100% for p63. All markers stained the various tumor components including spindle cells and the cells on the surface of and within the treated tumor bone matrix. Most markers were also positive in reactive-appearing woven bone adjacent to tumor: 84.6% for H3.3 G34W, 100% for SATB2, and 68% for p63. These findings suggest that denosumab treatment of giant cell tumor of bone results in osteoblastic differentiation with bone production.

Summary The distinction between lipoma and atypical lipomatous tumor can be challenging in some cases. While detection of MDM2 gene amplification via fluorescence in situ hybridization (FISH) has been well established as a diagnostic tool to distinguish atypical lipomatous tumor and well-differentiated liposarcoma from benign mimics, MDM2 RNA in situ hybridization (RNA-ISH) has recently been proposed as an alternative diagnostic assay. During clinical workup for lipomatous tumors using MDM2 RNA-ISH, we noticed several dysplastic lipomas that were positive for MDM2 RNA-ISH but negative for MDM2 amplification by FISH. In this study, we examined a series of 11 dysplastic lipomas, all confirmed to be negative for MDM2 amplification by FISH. Positive MDM2 RNA-ISH was noted in 10 (91%) dysplastic lipomas. Single-nucleotide polymorphism array on one dysplastic lipoma identified the presence of homozygous deletion of 13q, including the RB1 gene locus with no evidence of MDM2 copy number gain. Our findings on the discordance between MDM2 FISH and MDM2 RNA-ISH highlight the potential utility and pitfalls of using MDM2 RNA-ISH in the distinction of atypical lipomatous tumor and related liposarcomas from dysplastic lipoma.

This article assesses the water use impacts of the Conservation Reserve Enhancement Program in the Upper Arkansas River basin in Kansas, a water rights retirement program aimed at reducing depletion of the High Plains Aquifer. First, I use a fixed effects model with matched samples of farmers to determine the effect of the program on the water use of individuals who retire acreage. I find that every acre authorized for irrigation that is retired in the program represents about 1.28 acre‐feet of water that would have been used each year. Further, I do not find evidence that farmers increase their water use in an effort to satisfy program eligibility requirements. Second, I estimate a probit regression to determine which factors most influence the probability that a farmer retires a water right. Using the results of the probit regression, I then simulate enrollment decisions outside of the policy region to assess how features of the program impact its cost effectiveness and how the policy design could be improved. I find that programs that base incentives on past levels of water extraction lead to more water use reductions per dollar paid.

Summary Primary gastrointestinal liposarcoma is rare, and information regarding this entity is largely based on single case studies. We report on 8 patients with primary liposarcoma of the gastrointestinal tract and review the pertinent literature. The cohort includes 6 men and 2 women who ranged in age from 51 to 81 years (median 68.5). Two tumors arose in the stomach, 4 in the small intestine, and 2 in the large intestine. Tumors ranged in size from 2.5 to 14.5 cm (median 7 cm), originated in the submucosa or muscularis propria of the intestinal wall, and frequently protruded into the bowel lumen, resulting in mucosal ulceration and luminal obstruction. Six tumors were dedifferentiated liposarcomas, and 2 were well-differentiated liposarcoma. Surgical excision was performed on all tumors except for 1 case of dedifferentiated liposarcoma. On follow-up, 1 patient with dedifferentiated liposarcoma developed a lytic sacral lesion suspicious for metastasis 4 months after resection of the primary, and another underwent marginal resection and presented with recurrence 4 years later, had tumor re-resection, and was considered disease-free at 6 weeks postsurgery. A third patient with dedifferentiated liposarcoma was alive with unknown disease status at 17 months following surgery, and another patient with dedifferentiated liposarcoma was alive without evidence of disease at 30 months following surgery. No follow-up information on the remaining patients is available. Overall, liposarcomas of the intestinal tract are most frequently high-grade dedifferentiated tumors that are biologically aggressive and require surgical excision with widely negative margins to help reduce the risk of local recurrence and dissemination. Important in the differential diagnosis is malignant gastrointestinal stromal tumor. Care must be taken not to misdiagnose one entity for the other because the correct diagnosis carries important therapeutic implications.

Desmoplastic small round cell tumor (DSRCT) is a rare malignant tumor that occurs mainly in the retroperitoneum of children and young adults. In its prototypical form, DSCRT displays characteristic morphology with nested primitive small round cells in a desmoplastic stroma and a distinctive immunophenotype with polyphenotypic differentiation. However, DSCRT can also exhibit a broader clinical, histologic and immunohistochemical spectrum and, therefore, cause diagnostic difficulties. Given that DSCRT is an aggressive and nearly universally fatal disease, making the correct diagnosis is critically important. Herein, we report three patients with DSRCT and unusual clinical, morphologic or immunohistochemical characteristics, in order to highlight its remarkable diversity and increase awareness of this unusual, distinctive neoplasm.

Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms of the gastrointestinal tract, with a prevalence of 5% out of all sarcomas. We herein report the case of a 54-year-old man with metastatic GIST who initially presented to the emergency department with severe “anemia” CT examination revealed a 22 cm mass adherent to his small bowel and associated pelvic ascites and metastases. Surgical excision of the abdominal wall mass and partial omentectomy demonstrated extensive necrosis and a tumor mitotic rate of 17 per 5 mm2 . Molecular profiling of the primary mass showed a KIT exon 9 mutation. Despite eight years of sunitinib treatment, followup PET-CT evaluation showed three enlarging omental/peritoneal masses. Surgical excision and molecular profiling of each mass, opposed to the standard practice of profiling only one, demonstrated different KIT exon mutations between each mass, each with resistances to different tyrosine kinase inhibitor treatments. Article Highlights Metastatic gastrointestinal stromal tumor can attain novel mutations Performance of therapies may decline in the setting of novel KITmutations Molecular profiling of multiple metastatic nodules may aid in treating specific mutations

The use of denosumab to treat giant cell tumors of bone (GCT) and other giant cell-containing bone tumors has become more common. While the clinicopathologic features of denosumab-treated giant cell tumors of bone have been well-illustrated, descriptions of other denosumab-treated bone tumors are very limited. Surgical pathology files of two institutions and consultation files from two authors were searched for denosumab-treated aneurysmal bone cysts and denosumab-treated osteoblastomas. Clinicopathologic features were reviewed and analyzed. We identified four patients with denosumab-treated bone tumors other than GCT from our surgical pathology and consultation files, including two aneurysmal bone cysts and two osteoblastomas. All were treated with denosumab for 0.5-7.0 (median 4.5) months. Radiologically, denosumab-treated tumors showed decreased size with increased ossification and mineralization on CT and heterogeneous intermediate to hypointense signal on MRI. Histologically, denosumab-treated aneurysmal bone cyst contained thin, elongated, curvilinear, and anastomosing strands of bone with empty lacunae, while denosumab-treated osteoblastoma showed circumscribed nodules of woven bone lined by small osteoblasts. Denosumab-treated aneurysmal bone cyst and osteoblastoma showed treatment-related morphologic changes that can mimic other bone neoplasms. Their recognition requires correlation with the clinical history of denosumab use and radiologic findings.