Follicular dendritic cell sarcoma (FDCS) is a rare, mesenchymal neoplasm that may be nodal or extranodal in location. Lung involvement is rare. It is a slow-growing, painless tumor with a frequent capacity to recur and metastasize. We present a case of extranodal FDCS of the lung with an unusual presentation. A 34-year-old man presented with the complaints of haemoptysis and chest pain. A large left perihilar mass with endobronchial component was found on radiological evaluation. On endobronchial biopsy and mediastinal tru-cut biopsy, differential diagnoses of an inflammatory myo-fibrohistiocytic lesion and leiomyosarcoma were provided on the basis of morphological features of bipolar spindled cells arranged in intersecting fascicles and storiform patterns and immunophenotyping. A pneumonectomy was performed for the mass on which further immunohistochemical evaluation with CD21, CD35, and D2-40 finally helped form a diagnosis of FDCS. The patient recovered well from the surgery and has been on follow-up ever since. Owing to the rarity of this condition and its non-specific clinical features, FDCS is often misdiagnosed in the absence of appropriate immunohistochemistry. An of awareness of its morphological features and immunophenotype is, thus, necessary to provide early treatment and follow-up in order to prevent its recurrence and metastasis.

Superficial CD34-positive fibroblastic tumor (SCPFT) is a recently identified, infrequent, low-grade mesenchymal neoplasm, first identified in 2014. Although it is relatively new to the field, SCPFT has been gaining prominence in surgical pathology practice because of its distinctive features. As of now, there are limited reported cases of SCPFT, with fewer than 100 instances documented in scientific literature. This distinctive blend of rarity and intriguing variability in presentation emphasizes the significance of identifying and understanding this uncommon entity, facilitating precise diagnosis and optimal management. In this article, we aimed to present a notable case of SCPFT in a male in his 20s who presented with a distinct subcutaneous mass measuring 2.4 × 1.8 cm at the medial aspect of the knee joint. The patient reported no significant medical history or trauma to the affected area. MRI of the knee showed a well-defined 2.4 × 1.8 cm subcutaneous mass with no definite communication with the underlying ligament or meniscus. The histopathological examination revealed spindle cell neoplasm arranged in intersecting fascicles, accompanied by arborizing blood vessels. Neoplastic spindle cells exhibited marked nuclear pleomorphism, and abundant and eosinophilic cytoplasm, with focal areas of granular, glassy, and lipidized cytoplasm. Nuclear pseudo inclusions and a few mitotic figures (1-2 per high-power field) were noted. Inflammatory infiltrates were identified within the neoplasm, comprising eosinophils and lymphocytes, highlighting an immune response within the tumor microenvironment. The surgical margin exhibited involvement with the tumor infiltrates, with the neoplastic cells extending into the adjacent fat tissue. This finding indicates local tumor spread and potential challenges in achieving complete resection. Immunohistochemical staining showed positive staining for CD34, corroborating the diagnosis of a CD34-positive fibroblastic tumor. Focal positive staining for pan-CK was noted. Staining for CD31, smooth muscle actin (SMA), desmin, S100, and anaplastic lymphoma kinase (ALK) was negative, supporting the diagnosis. The Ki67 proliferation index was low.

Solitary fibrous tumors are rare tumors of pluripotent fibroblastic or myofibroblastic origin that generally arise among older individuals, with a mean age of onset ranging from 55 to 65 years. Though typically associated with pleural involvement, solitary fibrous tumors can emerge in virtually every anatomic location within the body. Although most solitary fibrous tumors are benign, approximately 20% may exhibit malignant features such as local invasion, recurrence, and metastases. In this article, we report the case of a 58-year-old male with a diagnosis of a retroperitoneal solitary fibrous tumor. We analyze computed tomography imaging findings and additionally correlate imaging features with the patient\'s unique pathological and genotypic findings to optimize diagnosis.

Introduction: Molecular analysis plays a growing role in the diagnosis of mesenchymal neoplasms. The aim of this study was to retrospectively apply broad, multiplex molecular assays (a solid tumor targeted next-generation sequencing [NGS]) assay and single nucleotide polymorphism [SNP] microarray) to selected tumors, exploring the current utility and limitations. Methods: We searched our database (2010-2020) for diagnostically challenging mesenchymal neoplasms. After histologic review of available slides, tissue blocks were selected for NGS, SNP microarray, or both. DNA and RNA were extracted using the AllPrep DNA/RNA FFPE Kit Protocol on the QIAcube instrument. The NGS platform used was the TruSight Tumor 170 (TST-170). For SNP array, copy number variant (CNV) analysis was performed using the OncoScanTM CNV Plus Assay. Results: DNA/RNA was successfully extracted from 50% of tumors (n = 10/20). Specimens not successfully extracted included 6 core biopsies, 3 incisional biopsies, and 1 resection; 4 were decalcified (3 hydrochloric acid, 1 ethylenediaminetetraacetic acid). Higher tumor proportion and number of tumor cells were parameters positively associated with sufficient DNA/RNA extraction whereas necrosis and decalcification were negatively associated with sufficient extraction. Molecular testing helped reach a definitive diagnosis in 50% of tumors (n = 5/10). Conclusions: Although the overall utility of this approach is limited, these molecular panels can be helpful in detecting a specific \"driver\" alteration.

Deep angiomyxoma is a rare, infiltrative, hormone-dependent, benign-mesenchymal neoplasm that occurs in the deep soft tissues of the perineal regions. In total, 33% females with newly diagnosed deep angiomyxoma will typically relapse within 5 years after the standard treatment of radical resection. Postoperative hormone therapy is frequently administered to prevent recurrence, but the role of prophylactic oophorectomy in premenopausal women remain to be fully elucidated. In the present report, a 42-year-old Japanese woman was referred for a refractory Bartholin\'s cyst that is 14 cm in diameter. Based on the results of imaging (unenhanced CT and MRI) and histopathology, deep angiomyxoma was suspected, but no definitive diagnosis was possible. Tumor resection and bilateral salpingo-oophorectomy were performed before the postoperative diagnosis was confirmed to be deep angiomyxoma. The patient received an aromatase inhibitor (2.5 mg letrozole daily) as adjuvant hormonal therapy. There was no evidence of recurrence at the 1-year postoperative follow-up. In conclusion, prophylactic oophorectomy and postoperative adjuvant therapy with aromatase inhibitors may be a promising treatment option for deep angiomyxoma to optimize the outcome of surgical treatment. Long-term follow-up is required to monitor for the late and/or local recurrence of deep angiomyxoma and possible adverse effects of adjuvant hormonal therapy.

BACKGROUND: Gastrointestinal stromal tumour (GIST) is the most common mesenchymal neoplasm arising in the stomach. However, a number of other rare mesenchymal neoplasms do occur at this anatomic site, which often presents a diagnostic challenge for cytopathologists on endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). Our study aims to selectively present the clinico-radiological and cytopathological characteristics of these rare \"non-GIST\" neoplasms, as well as their differential diagnoses.
METHODS: We performed a 20 year retrospective search in the cytopathology database of our two large medical institutions for non-GIST mesenchymal neoplasms arising in the stomach and diagnosed on EUS-FNA. Data regarding the patients\' demographics and radiological findings were analysed. All available cytopathology specimens were reviewed. The cytomorphological characteristics and the accompanying immunohistochemical stains, when available, were subsequently analysed.
RESULTS: Twenty-five cases of gastric mesenchymal tumours were selectively included in the study after excluding all cases of GIST (n = 113) diagnosed on FNA. These cases included 10 leiomyomas (40%), eight schwannomas (32%), five glomus tumours (20%), one perivascular epithelioid cell neoplasm, and one desmoid tumour. The specimen cellularity was variable and ranged from hypocellular to highly cellular. Most smears were composed of spindle cells with a few showing epithelioid morphology. Cell blocks were available in 20 cases and a range of immunohistochemical ancillary studies were performed. DOG-1, c-KIT, smooth muscle actin (SMA), and S100-protein were the most common immunomarkers done.
CONCLUSIONS: Our study highlights important cytomorphological characteristics of rare mesenchymal neoplasms arising in the stomach. In the appropriate clinical setting and with the help of immunohistochemistry, an accurate diagnosis of these neoplasms can be achieved.

Lipoblastoma-like tumor of the vulva (LBLTV) was first described as a benign mesenchymal neoplasia; it was not recognized as a separate diagnosis in the 2013 WHO classification of soft-tissue tumors. To date, only 19 cases have been reported. LBLTV differential diagnosis includes other tumors of the vulvoperineal region and tumors with adipocytic differentiation, most of which are benign and thus a misdiagnosis has few clinical consequences. However, LBLTV may also mimic some aggressive lipomatous neoplasms. We describe a case of LBLTV in a 28 year-old woman and review the literature.

The distinction of mesenchymal tumors of the uterus is a frequent diagnostic challenge in gynecologic pathology. Especially, distinguishing low-grade endometrial stromal sarcoma (ESS) from leiomyoma or distinguishing low-grade ESS from high-grade ESS can be difficult. Epithelial-mesenchymal transition (EMT) is a physiological and pathological process in which epithelial cells lose their morphological features, become elongated and acquire mesenchymal traits. The signaling pathway of Zinc finger E-box binding homeobox 1 (ZEB1) is one of the most significant pathways involved in the EMT process and it has a crucial role in cancer progression, metastasis, and therapy resistance. We studied a series of 69 uterine mesenchymal neoplasms including 18 endometrial stromal sarcomas (10 cases of low grade and 8 cases of high grade endometrial stromal sarcomas), 26 leiomyosarcomas (8 cases of grade 1 and 19 cases of grade 2-3 leiomyosarcomas), 15 leiomyomas, and 10 rhabdomyosarcomas, using an antibody ZEB1. We graded the leiomyosarcomas depending on the FNCLCC grading system. It was observed that leiomyosarcoma was more intensely stained with ZEB1 than leiomyoma (P < 0.001) and high-grade ESS was significantly more intensely stained with ZEB1 protein than low-grade ESS (P < 0.004). It also was observed that high-grade leiomyosarcoma was significantly more intensely stained with ZEB1 protein than low-grade leiomyosarcoma (P < 0.000). Our data suggest that Zeb1 can be used to differentiate high-grade sarcomas from their low-grade counterparts as well as benign and malignant smooth muscle tumors of the uterus.

Mimickers of neuroendocrine neoplasms (NEN) include a number of important pitfall tumors. Here, we describe our experience with mesenchymal mimics of NENs to illustrate their spectrum and draw the attention particularly to a group of mesenchymal/non-epithelial neoplasms (MN) that combine epithelioid histology with neuroendocrine (NE-) features and peculiar genetic abnormalities. In a consultation series of 4498 cases collected between 2009 and 2021, 2099 neoplasms expressing synaptophysin and/or chromograninA were reviewed and analyzed. A total of 364 (18%) were diagnosed as non-NENs, while the remaining tumors were NEN. The group of mesenchymal/non-epithelial neoplasms with NE-features (MN-NE) included 31/364 (8%) cases. These mostly malignant neoplasms showed an epithelioid morphology. While all but one tumor expressed synaptophysin, mostly patchy, only 10/29 (34%) co-expressed chromograninA. A total of 13/31 (42%) of the MN-NE showed EWSR1-related gene fusions (6 Ewing sarcomas, 5 clear cell sarcomas, and 1 desmoplastic small round cell tumor, 1 neoplasm with FUS-CREM gene fusion) and 7 (23%) were SWI/SNF (SMARCB1 or SMARCA4)-deficient neoplasms. The remaining MN-NE included synovial sarcoma, sclerosing epithelioid mesenchymal neoplasm, melanoma, alveolar soft part sarcoma, solitary fibrous tumor, and chordoma. A total of 27/31 MN-NE were from the last 8 years, and 6 of them were located in the pancreas. Eleven MN-NE were initially diagnosed as neuroendocrine carcinomas (NECs). MN-NE with epithelioid features play an increasing role as mimickers of NECs. They mostly belong to tumors with gene fusions involving the EWSR1 gene, or with SWI/SNF complex deficiency. Synaptophysin expression is mostly patchy and chromograninA expression is infrequent in MN-NE of this series and data extracted from literature.

Soft tissue sarcomas (STS) encompass a diverse family of neoplasms of mesenchymal origin, marked by significant heterogeneity in terms of physiopathology, molecular characterisation, natural history and response to different therapies. This review aims to summarise the current strategies for the management of patients with STS, including surgery, systemic treatments and radiation therapy, along with considerations applicable to the most frequent subtypes, as well as particularities associated with less common and specific histologies. It also provides insights into upcoming strategies to tackle this challenging group of diseases.