Neuroendocrine Tumors Research Articles

Solid pancreatic masses: What’s hidden beneath? Insights into rare pancreatic lesions

The diagnostic approach to solid pancreatic masses has significantly evolved from the era when a focal pancreatic mass was almost synonymous to pancreatic ductal adenocarcinoma, to a wide spectrum of pancreatic lesions, some of which have good prognosis. With the advent of advanced diagnostic tools, particularly refined imaging and tissue acquisition techniques, a broader spectrum of differential diagnoses has been recognized, encompassing conditions ranging from neuroendocrine tumors or inflammatory masses, to rare entities like metastatic clear cell sarcoma or solitary fibrous tumors. We herein discuss case reports of some rare pancreatic lesions, which were diagnosed by combining clinical and imaging features and endoscopic ultrasound-guided tissue sampling and confirmed on surgical specimens. Further reports on these rare pancreatic tumors will contribute to a better understanding of their pathogenesis and effective management.

P1.03G.01 Lurbinectedin Synergizes with Selinexor by Inhibiting DNA Damage Repair and Enhancing Immune Cell Infiltration in Neuroendocrine Lung Tumors

P1.03G.01 Lurbinectedin Synergizes with Selinexor by Inhibiting DNA Damage Repair and Enhancing Immune Cell Infiltration in Neuroendocrine Lung Tumors

A Comprehensive Review on Recent Advances in Management, Presentation, and Pathophysiology of Rectal Neuroendocrine Tumors

A Comprehensive Review on Recent Advances in Management, Presentation, and Pathophysiology of Rectal Neuroendocrine Tumors

An Update on Advances in Hypopituitarism: Etiology, Diagnosis, and Current Management.

This article provides an updated review of hypopituitarism (HP), an endocrine disorder characterized by a deficiency of one or more pituitary hormones. The various etiologies are reviewed, including pituitary neuroendocrine tumors (PitNETs), hypothalamic lesions, genetic mutations, and acquired factors such as head trauma, medications, neoplasms, and infiltrative diseases. It is noted that PitNETs are responsible for approximately half of the cases in adults, whereas in children the causes are predominantly congenital. Diagnosis is based on clinical evaluation and hormonal testing, with identification of the specific hormonal deficiencies essential for effective treatment. Laboratory tests present challenges and limitations that must be understood and addressed. Hormone replacement therapy is the mainstay of treatment, significantly improving patients' quality of life. It is important to know the possible interactions between hormone replacement therapies in HP. Recent advances in understanding the pathophysiology of HP and the importance of a multidisciplinary approach to the management of associated complications are discussed. This article emphasizes the need for comprehensive evaluation and continuous follow-up to optimize outcomes in patients with HP and highlights the importance of ongoing research to improve diagnostic and treatment strategies.

Application of LEF-1 immunohistochemical staining in the diagnosis of solid pseudopapillary neoplasm of the pancreas

IntroductionSolid pseudopapillary neoplasm (SPN) is a tumor of young females with gain-of-function mutation in catenin beta 1 gene involved in Wnt signal transduction pathway. Beta-catenin immunohistochemistry (IHC) is used to diagnose SPN. Lymphoid enhancer-binding factor 1 (LEF-1) has been recognized in the transactivation of Wnt pathway. We aim to study LEF-1 IHC in SPN and other pancreatic tumors and compare it with beta-catenin IHC. MethodsWe retrieved cases of SPN, pancreatic neuroendocrine tumor (PanNET), serous cystadenoma (SCA), ductal adenocarcinoma (PDAC) and acinar cell carcinoma (ACC) from 2011 to 2023. Formalin-fixed, paraffin-embedded blocks with adequate tumor were cut and stained with beta-catenin (B-Catenin-1 clone) and LEF-1 (EP310 clone) IHC. Cases were reviewed by two pathologists independently. Nuclear staining with LEF-1 and beta-catenin was considered as positive. ResultsOur cohort consisted of 111 cases [SPN = 59 (42 resections, 11 FNA, 6 biopsies), PDAC = 24, PanNET = 22, SCA = 5, ACC = 1]. For SPN cases male to female ratio was1:8. Age ranged from 9 to 81 years (average: 32 years). Pancreatic tail was the most common location (47 %) followed by head (28 %), body (19 %) and neck (6 %). Tumor size ranged from 1.0 to 12.2 cm (average: 5 cm). Among the SPN cases 57/59 demonstrated strong nuclear LEF-1 staining. 2/49 cases were negative for LEF-1 (both pathologist in agreement). All SPN tumors demonstrated nuclear staining with beta-catenin. Among the non-SPN tumors, beta-catenin showed nuclear staining in 2/52 cases (2 PDAC). The remaining 50 cases were negative for nuclear beta-catenin and demonstrated variable staining pattern with interpretation variability between the two pathologists. The sensitivity and specificity for LEF-1 were 97 % and 100 %, respectively, while for beta-catenin, they were 100 % and 96 % respectively. ConclusionCrisp nuclear staining of LEF-1 without background staining makes diagnostic interpretation relatively easy and accurate compared to beta-catenin IHC. This is further helpful for small biopsy samples to help differentiate SPN from mimickers such as PanNET. None of the non-SPN cases displayed nuclear LEF-1 rendering it a valuable adjunct to beta-catenin in the diagnostic evaluation of SPN.

P3.13C.09 First-Line Treatments for Advanced Pure Large Cell Neuroendocrine Tumors (LCNEC):Insights from a Global Clinico-Genomic Study

P3.13C.09 First-Line Treatments for Advanced Pure Large Cell Neuroendocrine Tumors (LCNEC):Insights from a Global Clinico-Genomic Study

Liver Metastasis Masking as Neuroendocrine Carcinoma (NEC) Predates Discovery of Intra/Peri-Thyroid Thymic Carcinoma (ITTC)

Abstract Introduction/Objective Intrathyroidal thymic carcinoma (ITTC) also known as Carcinoma showing Thymus-Like differentiation (CASTLE) is a rare malignancy comprising 0.1 to 0.15% of thyroid cancers. The WHO 5th Edition emphasizes that these tumors may also occur outside the thyroid typically at the lower pole Methods/Case Report Our aim is to show that NEC is a mimic of ITTC; that CD5, c-KIT (CD 117), p40, CK5/6 expression distinguishes ITTC from NEC, and that ITTC may at times express NE markers. Briefly, a 51-year-old man presented with hoarseness left neck mass and a PET avid liver lesion in 2016. Biopsy of the neck and liver masses revealed an infiltrating poorly differentiated “NEC” with similar morphology; positive for p53, chromogranin, and synaptophysin; negative for cam5.2, thyroglobulin, TTF-1, CD20, Pax5, CD3, CD5, S-100, calcitonin, CD56, p16, p63, c-KIT (CD117), AE1/3; and 100% staining for Ki-67. The patient underwent chemotherapy, responded well, remained under surveillance, and was symptom-free in the interim. A new 2.1 x 2.0 cm nodule appeared at the left thyroid lower pole after 6 years. The tumor was positive for CD5, CD117, p40, CK5/6, with > 95% Ki67 expression. Chromogranin, synaptophysin, CD56, thyroglobulin, calponin, TTF1, and Epstein Barr virus were negative and was overall diagnostic of ITTC Results (if a Case Study enter NA) NA Conclusion This shows the diagnostic dilemma of distinguishing ITTC from NEC which may share expression of neuroendocrine (NEC) markers and that positivity for CD5, c-KIT (CD117), p40, and CK5/6 are key diagnostic features of ITTC.

A 34-year-old woman with mucolipidosis type IV predisposing to a neuroendocrine tumor in the gastric fundus

Abstract Introduction/Objective Mucolipidosis type IV (MLIV) is a lysosomal storage disorder with a gastric phenotype. Patients develop achlorhydia and compensatory hypergastrinemia, with pathology showing vacuolated parietal cells with lysosomal inclusions. MLIV is caused by mutation of TRPML1, a lysosomal membrane calcium channel required for trafficking proton pumps to the apical surface in parietal cells. We report the first case of MLIV predisposing to a neuroendocrine tumor (NET). This novel finding could impact management of patients with this disease, who may require frequent monitoring for NETs. We also show that immunohistochemistry for TRPML1 and H+/K+ ATPase can be used in conjunction to identify gastric MLIV. We hope that our updated immunohistochemical tools can aid in diagnosis of this disease. Methods/Case Report 34-year-old woman with MLIV requiring endoscopic resection for an incidentally discovered gastric polyp. Pathology showed Grade 2 NET invasion into submucosa (pT1). Background mucosa showed markedly vacuolated parietal cells, ranging from unilocular to multilocular with up to 20 vacuoles per cell. We stained the patient’s and a control stomach with antibodies against the TRPML1 and H+/K+ ATPase proteins. The H+/K+ ATPase antibody highlighted healthy parietal cells in the control stomach with strong cytoplasmic signal, but strikingly outlined lysosomal inclusions in MLIV parietal cells. TRPML-1 antibody showed cytoplasmic staining in parietal cells in the control. However, TRPML-1 staining showed markedly decreased signal in the patient and nuclear staining, possibly representing mislocalization. Results (if a Case Study enter NA) NA Conclusion We present the first case of MLIV predisposing to a NET in the stomach. NETs have potential for metastatic spread with subsequent mortality risk. Clinicians should maintain suspicion for NET development in this population, and protocols for frequent surveillance should be considered. This is also the first report using immunohistochemistry for TRPML1 and H+/K+ ATPase in combination to identify affected parietal cells in MLIV. Possibly, these tools can be used in the future by pathologists to diagnose MLIV.

A Rare Case of Sinonasal Large Cell Neuroendocrine Carcinoma with Lymph Node Metastasis

Abstract Introduction/Objective Sinonasal carcinomas comprise less than 1% of cancers, and the most common types are squamous cell carcinoma at 51.6% and adenocarcinoma at 12.6%. There are only limited published reports of sinonasal large-cell neuroendocrine carcinoma (LCNEC). This entity has distinguishing immunohistochemical and histomorphologic features; it stains positively for neuroendocrine markers (i.e., synaptophysin and CD56) and histologically has abundant amphophilic cytoplasm with prominent nucleoli. Methods/Case Report We present a 60-year-old female patient who was evaluated for a submandibular neck lump. Computed tomography identified a 3.2 x 1.8 x 1.6 cm enhancing lesion with central necrosis in the right submandibular space, representing either an enlarged necrotic right submandibular lymph node or a neoplasm arising from the right submandibular gland. The pathology of the lymph node biopsy was consistent with metastatic high- grade neuroendocrine carcinoma. The neoplastic cells stained positively for INSM1, CK8/18, CK AE1/3 (subset), TTF- 1, and Ki-67 (50%). Dotatate positron emission tomography showed evidence of focal activity in the right anterior nasal cavity supporting evidence with primary nasal cavity origin. Nasal endoscopy was performed, visualizing an area of necrotic friable tissue. Pathology confirmed the presence of large cell neuroendocrine carcinoma in the right nasal biopsies with metastatic LCNEC in right neck levels 1, 2A, 2B, 3, and 4. The malignant cells on hematoxylin and eosin stain had similar morphology to those in the initial lymph node biopsy, supporting a diagnosis of LCNEC. Results (if a Case Study enter NA) NA Conclusion Sinonasal large-cell neuroendocrine carcinomas are extremely rare. Upon literature search, there have been fewer than ten case reports published of this entity. Furthermore, large-cell neuroendocrine carcinoma behaves aggressively, and diagnosing this entity could result in earlier intervention and better patient outcomes. Highlighting the possibility of this diagnosis could broaden differentials in neoplasms that arise from the nose.

Detection of cardiac neuroendocrine tumour metastases by somatostatin receptor PET/CT: a systematic review and meta-analysis.

Cardiac neuroendocrine tumour metastases (CNTM) are rare, but advancements in molecular imaging including somatostatin receptor PET/CT (SSTR-PET/CT) could lead to a more frequent identification. The aim of this article is to perform a systematic review and meta-analysis on the detection of CNTM by SSTR-PET/CT. A comprehensive literature search of studies on CNTM detected by SSTR-PET/CT was carried out. Three different bibliographic databases were screened (Cochrane library, PubMed/MEDLINE, EMBASE) until 20 August 2024. Two review authors independently selected the eligible original articles and performed the quality assessment and the data extraction. Main findings of eligible studies were summarized and a proportion meta-analysis on the prevalence of patients with CNTM among those with neuroendocrine neoplasm (NEN) performing SSTR-PET/CT was carried out using a random-effects model. Ten articles reporting data on 163 patients with CNTM were included in the systematic review. SSTR was able to detect CNTM earlier compared to other radiological imaging techniques. Most patients with CNTM had other metastatic sites and CNTM were often asymptomatic. The meta-analysis of seven articles demonstrated a pooled prevalence of 1.5% (95% confidence interval: 1.0-1.9%) of patients with CNTM (n = 119) among those performing SSTR-PET/CT for NEN (n = 9,300). Moderate statistical heterogeneity was found (I 2 test: 62%). Evidence-based data demonstrate that SSTR-PET/CT enables early and better detection of CNTM compared to other radiological imaging methods. CNTM are encountered with a pooled prevalence of 1.5% of NEN patients performing SSTR-PET/CT. Prospective and multicentric studies are warranted to better clarify the impact of CNTM detection by SSTR-PET/CT on overall survival and clinical decision-making in NEN patients.

Nationwide questionnaire survey on pediatric pancreatic tumors in Japan.

Pediatric pancreatic tumors are rare and account for < 0.1% of all childhood cancers. The primary treatment for pancreatic tumors is surgical resection. However, because of the lack of knowledge regarding pediatric pancreatic tumors, no comprehensive treatment plans for pediatric pancreatic tumors have been developed. To compared the clinical features, treatment methods, and prognosis of pediatric pancreatic tumors in Japan with those in other countries. Questionnaires were sent to 213 pediatric surgical units in Japan. Pancreatic tumors that were not surgically treated were excluded from the survey. The primary survey investigated the number of patients aged 0-18 years who underwent pancreatic tumor surgery and the type of tumors managed during the 22-year study period (from January 1, 2000 to December 31, 2021) by post card. The secondary survey assessed the clinical images, treatment methods, and tumor outcomes via email. The primary survey enrolled 228 patients. In the secondary survey, 213 patients were eventually enrolled. The most common type of pancreatic tumor was solid pseudopapillary neoplasm (SPN) [n = 164 (77.0%)], followed by pancreatoblastoma [n = 16 (7.5%)], pancreatic endocrine tumor [n = 14 (6.6%)], non-epithelial tumor [n = 9 (4.2%)], pancreatic tumor [n = 7 (3.3%)], and metastatic pancreatic tumor [n = 3 (1.4%)]. Overall, 123 (57.7%) patients underwent distal pancreatectomy, of whom 49 underwent laparoscopic surgery. Forty-four (20.7%) patients underwent enucleation, of whom eight underwent laparoscopic surgery. Thirty-two (15.0%) patients underwent pancreaticoduodenectomy, of whom one underwent laparoscopic surgery. All patients with SPN, including those with distant metastases and recurrent disease, survived. SPN was more common in Japan than in other countries. Regardless of the histological type, resection is the most effective treatment for pediatric pancreatic tumors.

Conclusive evidence for the origin of the carcinoid component in strumal carcinoids and a new morphological pattern

Abstract Introduction/Objective There has been debate whether strumal carcinoids are carcinoids with areas resembling thyroid or arise from bonafide thyroid tissue in struma. While the thyroid nature has been proven by demonstrating positive TTF-1 in the struma component, evidence for the origin of the carcinoid component is sparse. Herein, we describe a case of strumal carcinoid and use a panel of markers to show definitive morphological and immunohistochemical evidence of the evolution of the neoplasm from struma ovarii to struma carcinoid, within the same lesion. We also report a unique component of a more sinister single cell pattern of invasion apart from the usual insular, trabecular, and mucinous patterns. Methods/Case Report A 40-year-old woman with an adnexal mass underwent bilateral salpingo- oophorectomy/hysterectomy. Microscopic analysis identified thyroid tissue consistent with struma ovarii, juxtaposed with a neuroendocrine neoplasm. The interface between the two showed strong PAX-8 and uniform TTF-1 staining in the struma but gradual loss of TTF-1 with retained/weak PAX-8 staining, moving away from the struma component and into the carcinoid. Additionally, a pattern of single cell invasion was identified, away from the main tumor and at the ovarian surface. These cells closely resemble luteinized ovarian stromal cells but are stained like the carcinoid tumor. Two months postoperatively, the patient had no evidence of recurrence or metastasis. Results (if a Case Study enter NA) NA Conclusion We have provided conclusive morphological and immunohistochemical evidence that strumal carcinoid develops from native neuroendocrine cells of thyroid tissue in struma ovarii. Specifically, retained/weak PAX-8 with interspersed TTF-1 in an adnexal carcinoid provides valuable insight when dealing with tumors of unknown etiology, strongly favoring an ovarian primary (specifically, from struma ovarii) and not metastasis from the gastrointestinal tract or other Mullerian tissue. Lastly, the single cell pattern of invasion that we elucidate here is something to be aware of in the context of metastases or frozen sections.

CK20-negative Merkel Cell Carcinoma with Concomitant Squamous Cell Carcinoma In-Situ and Metastasis to the Parotid Gland

Abstract Introduction/Objective This report presents a patient with an aggressive CK20-negative neuroendocrine tumor of the dermis with metastasis to the parotid gland and a concomitant squamous cell carcinoma in-situ (SCCIS) and highlights diagnostic challenges of CK20-negative tumors. Methods/Case Report A centennial female with a history of non-melanoma skin cancer and leukemia presented to the dermatology clinic with a one-year history of an enlarging skin lesion on her right cheek and a subcutaneous mass on the right central lateral neck. On examination, the lesion appeared as a rough and raised red papule with a central crust. On CT, a large heterogeneously enhancing right parotid mass with surrounding satellite nodules, adjacent necrotic adenopathy, and an ulcerating subcutaneous mass in the adjacent right face. An incidental 3 mm right upper lobe nodule was identified. The pathology report noted two distinct malignant neoplasms within the specimen. Microscopy revealed ulceration with acanthosis and full thickness keratinocyte atypia, suggesting Bowen’s disease. On microscopic examination of the separate dermal tumor, there were sheets of uniform small cells with a high nuclear to cytoplasmic ratio and scant cytoplasm. IHC staining was positive for the neuroendocrine markers AE1/AE3, CAM5.2, synaptophysin, and CD56. CK20, CK7, and TTF-1 were negative. As some MCC may be negative for CK20, CK20 was performed twice. Differential diagnoses included SCCIS with CK20-negative MCC versus a metastatic neuroendocrine carcinoma of parotid gland to the skin. The patient transitioned to hospice care soon after the diagnosis. Results (if a Case Study enter NA) NA. Conclusion Our patient presents with an interesting case of a CK20-negative MCC with metastasis to the parotid gland. Since CK20 was stained negative twice, it complicated the diagnosis of MCC vs. small cell carcinoma. We suspected a more likely diagnosis of MCC metastasis to the parotid gland due to multiple reported cases (Day et al. 2016). Our patient also had an identifiable Bowen’s disease borderline to the neuroendocrine carcinoma. It is well known of the coexistence of MCC and squamous cell carcinoma in a cutaneous lesion (Suaiti et al. 2019). Thus, a metastatic MCC to the parotid gland is more likely in this case. As MCC is an aggressive cancer that metastasizes quickly, accurate diagnosis is crucial. With recent literature reporting the association of CK20-negativity with VN-MCC, and the presence of UV signature mutations in CK20- negative MCC, genomic screening would be a useful diagnostic tool.

SMARCA4-Deficient Undifferentiated Carcinoma of the Gastroesophageal Junction: A Case Report

Abstract Introduction/Objective To report a rare case of the newly characterized variant of gastric carcinoma; undifferentiated carcinoma with intact SMARCB1 (INI1) but lost SMARCA4/SMARCA2, and approach to diagnosis. Methods/Case Report A case of gastric mass extending to the gastroesophageal junction, microscopically, showing sheets of atypical, medium to large, discohesive, polygonal cells with large eccentric and pleomorphic nuclei, variably prominent nucleoli, and eosinophilic cytoplasm with brisk mitosis, in the background of marked necrosis and granulomatous inflammation. And having focally positive staining for cytokeratin and negative for melanoma, diffuse large B-cell lymphoma, high grade neuroendocrine tumor, sarcoma, rhabdoid/myoid-specific immunohistochemistry (IHC) markers. The case was further characterized with immunophenotypic, cytogenetic, and molecular findings. Results (if a Case Study enter NA) By immunohistochemistry (IHC), the large tumor cells were positive for vimentin, FLi-1 and patchy CD71. A subset of tumor cells showed CD34 positivity. The tumor cells were mainly negative (with rare focal positivity) for all cytokeratin including (CK AE1/AE3, EMA, and CK OSCAR). Tumor cells were negative for specific markers for melanoma, GIST, sarcomatous tumors, squamous cell carcinoma, hematolymphoid malignancies, and neuroendocrine tumors. EBER-ISH and HHV-8 were negative. The Ki67 showed a proliferative index of ~60%. The tumor cells demonstrated retention of INI1 (SMARCB1) with loss of both SMARCA2 and SMARCA4 by IHC. Molecular studies detected an inactivating mutation of the retinoblastoma-1 gene (RB1 I124Rfs*6) and TP53 with altered function compared to wild-type (TP53-G245S) with no mutations or deletion of SMARCB1 gene. The status of SMARCA4 gene came as indeterminate. No microsatellite Instability detected. Conclusion Our study demonstrates the challenge of diagnosing the SMARCA4/SMARCA1-deficient undifferentiating gastric carcinoma especially with negative cytokeratin stains, showing the immunohistochemistry profile of the tumor and its molecular findings in our case.

A Curious Case of Pancreatoblastoma in an Older Age Woman

Abstract Introduction/Objective Pancreatoblastoma is a malignant epithelial neoplasm of the pancreas and displays multiple lines of differentiation with acinar differentiation as the predominant pattern. The squamoid nests are considered a defining component of pancreatoblastoma. Pancreatoblastoma is seen most often in children, however, rare cases in adults have been described in the literature. In children, most pancreatoblastomas are indolent and curable, however, the prognosis is worse in adults due to the presence of frequent metastasis. Methods/Case Report We report an interesting case of pancreatoblastoma in a 65-year-old woman with no pertinent medical history who presented with abdominal discomfort. MRI abdomen showed an 11.3 cm mass with central necrosis within the head of the pancreas. Fine-needle aspiration (FNA) of the mass showed monotonous cells with neuroendocrine differentiation and FNA was signed out as a low-grade neuroendocrine tumor (NET). The patient underwent a Whipple resection for a presumed NET. On gross examination, a 14 cm large solid, fleshy, lobulated, partially encapsulated mass was noted in the head of the pancreas. H&amp;E slides on low power showed the tumor composed of highly cellular lobules separated by fibrous bands. Within the lobules, the neoplastic cells predominantly had an acinar differentiation with focal trabecular or solid areas. Dispersed within the tumor were squamoid nests composed of plump to spindle-shaped cells with abundant eosinophilic cytoplasm arranged in whorls. Immunohistochemical stains demonstrated squamoid nests being positive for CK5/6 and had a nuclear-staining pattern with beta-catenin. The remaining tumor was positive for trypsin, chymotrypsin, BCL-10, synaptophysin (focal), chromogranin (focal), and INSM-1 (patchy). On MSK-Impact (next- generation sequencing), a mutation in CTNNB1 was detected. Results (if a Case Study enter NA) NA Conclusion In adults, it is important to consider pancreatoblastoma in the differential diagnoses of solid pancreatic tumors while being cautious not to confuse it with neuroendocrine tumor or acinar cell carcinoma. The presence of squamoid nests is critical for its diagnosis. Making a diagnosis of pancreatoblastoma through FNA or pancreatic biopsy can be exceptionally challenging in cases lacking squamoid nests.

Solitary fibrous tumor of the stomach

Abstract Introduction/Objective Solitary fibrous tumor (SFT) is an uncommon fibroblastic tumor that originates from the mesenchymal tissue. It has been rarely reported within the stomach. None of these reported tumors have occurred in a background of autoimmune atrophic gastritis as was seen in our patient. Methods/Case Report Case report Results (if a Case Study enter NA) An 85-year-old female with history of anemia and autoimmune atrophic gastritis presented with two-month history of dysphagia and abdominal discomfort. Upper gastrointestinal endoscopy showed a 1 cm subepithelial lesion in the gastric body along the greater curvature. Upper endoscopic ultrasound showed mildly hypoechoic lesion in the submucosa of the stomach with the differential of leiomyoma, neuroendocrine tumor, gastrointestinal stromal tumor, and an atypical looking lipoma. The entire gastric lesion was lifted with submucosal saline injection and then resected using cap endoscopic mucosal resection (EMR) snare cautery. Gross examination showed a well-circumscribed lesion with firm, tan-white cut surface. On microscopy, a bland appearing spindle cell proliferation within a collagenous stroma was seen with alternating hypercellular and hypocellular areas and few dilated vessels. No significant mitosis, nuclear pleomorphism or necrosis was identified. Immunohistochemical stains were performed and the lesional cells were positive for STAT6. Markers for gastrointestinal stromal tumor (CD117, DOG1), smooth muscle tumor (desmin, smooth muscle actin) and schwannoma (S100, SOX10) were negative. Nuclear staining for STAT6 is a sensitive and specific marker for SFTs. This particular SFT was considered to be of low risk and non-malignant considering its small size, lack of mitotic activity and tumor necrosis. The etiology for SFT is not entirely clear but molecular studies have shown that the NAB2::STAT6 translocation in a spindle cell neoplasm is a diagnostic hallmark for SFTs. Conclusion Solitary fibrous tumors have been rarely reported within the stomach. Complete surgical resection with negative margins is the mainstay of treatment as they may recur after an incomplete resection.

Atypical Gastric Glomus Tumor of Uncertain Malignant Potential in A 16-Year-Old Female; A Rare Entity with Unique Findings

Abstract Introduction/Objective Gastric glomus tumor (GGT) is a rare mesenchymal tumor that is challenging to diagnose, especially when the immunoprofile overlaps with other more common gastric mesenchymal tumors. The majority of GGT are benign, however, rarely it can be atypical or even malignant. Herein, we present a case of a young female with atypical gastric glomus tumor of uncertain malignant potential. Methods/Case Report A 16-year-old female presented to the emergency with abdominal pain, coffee ground emesis, and melena. Imaging showed a 3.2 cm well-defined gastric mass arising from the muscularis propria. Results (if a Case Study enter NA) The FNA biopsy revealed clusters of tumor cells with uniform characteristics, exhibiting distinct cell membranes and eosinophilic to clear cytoplasm, surrounding prominent vasculature. Immunohistochemical analysis showed that the tumor cells were positive for SMA, synaptophysin, vimentin, calponin, and caldesmon, with weak, patchy positivity for DOG1. CD34 highlighted the vessels separating the tumor cellular clusters into lobules. CD117 and Desmin were negative. The Ki67 proliferation index varied with hotspot foci 25-30%. Morphology and immunoprofile suggest glomus tumor, however, neuroendocrine tumor and epithelioid GIST needed to be excluded. Subsequent resection specimen showed that the tumor was located within the muscularis propria with extension into the serosal vessels, suggesting vascular invasion, along with foci of cellular spindling and nuclear irregularity are identified. No necrosis noted. Tumor cells were positive for cyclin D1 while negative for myogenin, chromogranin, and DOG1. Overall, findings were consistent with GGT of uncertain malignant potential. Conclusion Although GGT are rare, they should be considered in the differential diagnosis of gastric mesenchymal tumors. The presence of diffuse SMA staining can help distinguishing them from GIST. It is crucial to scrutinize for signs of cellular and nuclear atypia, particularly in deeply seated glomus tumors.

NEUROENDOCRINE TUMORS OF THE GENITOURINARY TRACT - A CLINICAL AND PATHOLOGIC REVIEW

Abstract Introduction/Objective Neuroendocrine tumors (NETs) of the genitourinary (GU) tract are rarely seen during daily surgical pathology sign-out sessions and comprise a heterogeneous group of neoplasms. We undertook a retrospective study to assess the clinical and pathologic characteristics of this unusual group of neoplasms involving the GU tract. Methods/Case Report We performed a retrospective review of the surgical pathology files for NETs of the GU tract between July 1993 and December 2021. Chart review was performed for the clinical and pathologic findings. Results (if a Case Study enter NA) A total of 26 patients were identified. There were 18 males and 8 females ranging in age from 43 to 94 years (mean age 69 years). 19/26 (73%) cases were primary tumors; 9 bladder small cell carcinoma, 5 prostatic small cell carcinoma, 4 bladder paragangliomas, and 1 case of small cell carcinoma of the renal pelvis. 7/26 (27%) cases were metastatic tumors; 5 Merkel carcinoma (3 urinary bladders, 2 testes), and 2 small cell carcinoma of the lung to the kidney. Conclusion The majority of NETs of the GU are primary and urinary bladder to be the most common site. Merkel cell carcinoma appears to have a tendency to metastasize to the GU tract, especially to the testis.

Appendiceal Mucosal Schwann Cell Proliferation Associated with Incidentally Detected Goblet Cell Adenocarcinoma of Appendix in a Case of Invasive Adenocarcinoma of Sigmoid Colon- A Case Report

Abstract Introduction/Objective Appendiceal mucosal Schwann cell proliferation has been suggested to be a putative histologic marker of appendiceal diverticular disease. Appendiceal Goblet cell adenocarcinoma, (GCA) is amongst the most rare appendiceal tumors with a reported incidence of 0.05 cases per 100,000 population per year in United States. They have features of both neuroendocrine tumors and adenocarcinomas, but behave more similarly to adenocarcinomas. Methods/Case Report Herein, we report a case of appendiceal mucosal schwann cell proliferation associated with incidentally detected Goblet cell adenocarcinoma of appendix in a known case of invasive adenocarcinoma of sigmoid colon. A 75-year-old female presented with sigmoid colon obstruction. Intraoperatively, she was found to have gangrenous and perforated colon, as well as a large obstructing sigmoid mass, and underwent total abdominal colectomy with end-ileostomy. On gross examination, a tan bosselated tumor (up to 3.5 cm) was seen in proximal sigmoid colon. Microscopic examination showed Invasive adenocarcinoma, moderately-differentiated. Appendix was unremarkable on gross examination. Incidentally, the appendix microscopically demonstrated “Goblet cell adenocarcinoma”, histologic grade 1 out of 3 (pathologic stage pTis pN0), present in multiple foci within lamina propria of the distal third of appendix over an area measuring 1.5 cm. Additionally, there were foci of SOX10-positive bland- looking spindle cell proliferation in lamina propria of the appendix. This proliferation is rendered as “Schwann cell proliferation”. Results (if a Case Study enter NA) NA Conclusion One study found that “Schwann cell proliferation” is seen in 42% of appendiceal diverticula cases. It has never been reported in association with “Appendiceal GCA” before. Here we report an intriguing case of Schwann cell proliferation associated with this rare entity of GCA for the first time in literature. Therefore, awareness of such coexistence of these pathologic entities in the same appendix is essential to alert the pathologist to look for GCA, whenever Schwann cell proliferation is encountered in random section of an appendix. This case also emphasizes the importance of being vigilant of the possible presence of other tumors in a specimen with a known tumor.

YAP1 Status Defines Two Intrinsic Subtypes of LCNEC with Distinct Molecular Features and Therapeutic Vulnerabilities.

Large cell neuroendocrine carcinoma (LCNEC) is a high-grade neuroendocrine malignancy that, like small cell lung cancer (SCLC), is associated with the absence of druggable oncogenic drivers and dismal prognosis. In contrast to SCLC, however, there is little evidence to guide optimal treatment strategies, which are often adapted from SCLC and non-small cell lung cancer approaches. To better define the biology of LCNEC, we analyzed cell line and patient genomic data and performed IHC and single-cell RNA sequencing of core needle biopsies from patients with LCNEC and preclinical models. In this study, we demonstrate that the presence or absence of YAP1 distinguishes two subsets of LCNEC. The YAP1-high subset is mesenchymal and inflamed and is characterized, alongside TP53 mutations, by co-occurring alterations in CDKN2A/B and SMARCA4. Therapeutically, the YAP1-high subset demonstrates vulnerability to MEK- and AXL-targeting strategies, including a novel preclinical AXL chimeric antigen receptor-expressing T cell. Meanwhile, the YAP1-low subset is epithelial and immune-cold and more commonly features TP53 and RB1 co-mutations, similar to those observed in pure SCLC. Notably, the YAP1-low subset is also characterized by the expression of SCLC subtype-defining transcription factors, especially ASCL1 and NEUROD1, and as expected, given its transcriptional similarities to SCLC, exhibits putative vulnerabilities reminiscent of SCLC, including delta-like ligand 3 and CD56 targeting, as is with novel preclinical delta-like ligand 3 and CD56 chimeric antigen receptor-expressing T cells, and DNA damage repair inhibition. YAP1 defines distinct subsets of LCNEC with unique biology. These findings highlight the potential for YAP1 to guide personalized treatment strategies for LCNEC.