(1) Background: A malignant gastrointestinal neuroectodermal tumor (GNET) is an ultra-rare primary neoplasm with a distinctive histopathological, immunohistochemical, molecular, and ultramicroscopic profile, synonymous terminology with clear cell sarcoma-like tumor of the gastrointestinal tract. This case report aims to describe a case of GNET with challenging mesenchymal, lymphoid, and melanic tumor differential diagnosis. (2) Case presentation: We discuss the case of a 67-year-old male patient who presented with diffuse abdominal pain, intermittent lack of intestinal transit, and frequent episodes of nausea, followed by segmental resection of the jejunum and sigmoid colon. The patient had no relevant medical history. The surgical specimen underwent immunohistochemical staining and morphological evaluation. (3) Results: Histopathological analysis reveals a moderately homogeneous polyhedral-epithelioid and spindle cell neoplastic proliferation with a zonal discohesive pattern and extensive and focal fasciculated architecture. Twenty monoclonal antibodies were used for immunostaining, which allowed GNET to be diagnosed on the basis of the tumoral immune profile, characterized by positive reactivity of S100, SOX10, and CD 56. (4) Conclusions: The poor prognosis of GNET is highlighted in the present study, along with the vital importance of differential diagnosis issues with mesenchymal, lymphoid, and melanic tumors, which make the diagnosis difficult for both pathologists and clinicians.

Rationale: Monomorphic epitheliotropic intestinal T-cell lymphoma, formerly known as enteropathy-associated T-cell lymphoma, is an extremely rare, aggressive peripheral extranodal T-cell lymphoma, that is infrequent in native European and Caucasian populations. The current study presents the clinicopathological features, diagnostic approach, and clinical outcomes of this rare entity of lymphoma and highlights the importance of the early diagnosis of monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL).Patient concerns: Main symptoms and/or important clinical findings: We present the case of a 69-year-old male patient presenting with an abdominal mass, intestinal transit disorder, and weight loss. The abdominal computed tomography (CT) revealed features suggestive of a malignancy. Following clinical and imaging investigations, surgical resection of the small intestine with other areas of involvement has been performed and further to the histopathological examination and immunohistochemical testing are mandatory.Diagnoses and Interventions: Histopathological evaluation of the tumor revealed a proliferation of medium-to largesized monomorphic lymphocytes, with vesicular nuclei, prominent nucleoli, and a moderate amount of clear to pale eosinophilic cytoplasm, with an association of infrequent Reed-Sternberg-like cells. Immunohistochemical assessment of the aforementioned tumor using CD3, CD8, CD5, CD20, and CD30 confirmed the T cell proliferation line and the monomorphic epitheliotropic intestinal T-cell lymphoma diagnosis.Lessons: The current report highlights the importance of early diagnosis of MEITL owing to its poor prognosis and presents histopathological features that help distinguish MEITL from inflammatory bowel diseases and less aggressive T-cell lymphomas.

Rationale: In the era of antiretroviral therapy, lymphoma is the primary cause of cancer-related death among human immunodeficiency virus (HIV)-infected people and the most prevalent and aggressive non-Hodgkin lymphoma is diffuse large B cell lymphoma, which usually has an aggressive clinical course. CD5-positive diffuse large B cell lymphoma (DLBCL) is an insufficiently studied, relatively new entity, which accounts for 5% to 10% of the DLBCL population. The current study presents the clinicopathological features, diagnostic approach, and clinical outcomes of this HIV-related lymphoma and highlights the importance of the early diagnosis of CD5-positive DLBCL.Patient concerns: We present a case of a 30-year-old male patient, with a medical history of HIV-positive serology and antiviral treatment, presenting with diffuse abdominal pain and symptoms related to obstruction or perforation, followed by exploratory laparotomy and surgical resection of the small intestine with other areas of involvement. The surgical specimen was morphologically evaluated and immunohistochemical stained.Diagnoses and Interventions: Histopathologic examination revealed a diffuse neoplastic proliferation of large B lymphocytes within the small intestine, lacking features of other defined types of large B cell lymphoma. The diagnosis of CD5-positive DLBCL subtype was made after immunostaining with twelve monoclonal antibodies (CD3,

Introduction. Multiple primary malignant neoplasms are an uncommon phenomenon, given the very low incidence of two or more different tumors, while neoplasm may be limited to a single organ or may involve multiple separate anatomical organs. The main purpose of this study is to highlight the importance of morphological and immunohistochemical tests to distinguish the origin of the primary tumor. Case Presentation. We report the case of a 65-year-old deceased male, presenting multiple tumors in the lung, stomach, kidneys, and adrenal organs. The main symptoms presented by the patient were dyspnea with a range of 77% with oxygen saturation, fatigability, and productive cough. Histopathological examination revealed a solid and papillary lung adenocarcinoma, concurrent with tubular gastric adenocarcinoma. Immunohistochemical testing was mandatory by using a panel of seven monoclonal mouse antibodies (TTF-1, Napsin A, CK7, CK20, p40, synaptophysin, and chromogranin A). The pulmonary tumoral immunophenotype (positive for TTF-1, Napsin A, CK7; negative for CK20, p40, synaptophysin, and chromogranin A) confirms the diagnosis of primary lung ADC and invalidates the hypothesis of a metastasis arisen from a gastric adenocarcinoma or other forms of lung cancer. Conclusion. The importance of the ancillary test is to distinguish a primary tumor from a metastatic one.