Lynch syndrome (LS) is an autosomal dominant cancer predisposition syndrome caused by germline mutations in DNA mismatch repair genes or, less commonly, EPCAM deletions. LS-associated colorectal carcinomas often present at a young age and may show unusual histomorphological patterns, posing diagnostic challenges. We report a rare case of a 29-year-old female with EPCAM-mutated LS presenting as colonic adenocarcinoma with neuroendocrine-like rosette formation. The tumor initially mimicked mixed adenoneuroendocrine carcinoma (MANEC) due to biphasic histology and the presence of multiple rosettes. However, immunohistochemistry demonstrated negativity for synaptophysin and chromogranin, excluding true neuroendocrine differentiation with diffuse Pan CK and focal CDX2, CK20 positivity along with loss of MSH2 and MSH6. Further molecular analyses confirmed EPCAM exon 5-9 deletion. The tumor was ultimately classified as an MMR-deficient adenocarcinoma with pseudoendocrine morphology. This case broadens the histomorphological spectrum of LS-associated colorectal carcinomas and introduces the concept of a possible pseudoendocrine carcinoma arising in an epithelial malignancy. Recognition of this pattern is crucial to prevent misdiagnosis as MANEC, to guide appropriate management, facilitate familial screening, and highlight that not every rosette signifies neuroendocrine differentiation; some may represent LS in disguise.

Interdigitating dendritic cell sarcoma (IDCS) is a rare malignancy originating from dendritic cells, which participate in immune response activity as antigen-presenting cells by stimulating T lymphocytes. We report the case of a 24-year-old man who experienced an involuntary 20 kg weight loss over 2 months, combined with a steadily growing, painless lump in his right upper abdomen. Upon examination, a hard, nontender, immobile mass measuring 16 × 16 cm was found in the right hypochondrium. A massive, well-defined hypodense lesion covering all segments of the liver's right lobe was excised and was diagnosed as IDCS due to its characteristic histomorphological and immunohistochemical features.

Meissnerian neurofibroma is an extremely rare histological variant of neurofibroma, with less than ten reported cases of prominent differentiation toward pseudo-meissnerian bodies in the literature. The presence of focal or sparsely scattered pseudo-meissnerian bodies in neurofibromas is well documented in diffuse and plexiform types. It is also seen in various peripheral nerve sheath tumors, including schwannomas, as well as in congenital melanocytic nevi and neural crest hamartomas. The complete excision of the lesion is considered to be curative. We hereby present a rare case of prominent meissnerian differentiation in neurofibroma in a 26-year-old female.

Primary neuroendocrine tumors (NETs) of the kidney are exceedingly rare, with an estimated incidence of only 0.13 per 1 million individuals. Their rarity is attributed to the absence of native neuroendocrine cells within the renal parenchyma. These tumors span the WHO grading spectrum, with well-differentiated lesions reported most frequently. They may also occur in association with congenital anomalies such as horseshoe kidney. In this study, we present a new case of a 33-year-old female diagnosed with a primary renal NET at our hospital. She underwent imaging studies, surgical excision, and histopathological and immunohistochemical analysis. The findings suggest that these tumors are rare and have nonspecific clinical and imaging features. The diagnosis heavily relies on immunohistochemical analysis. Primary renal well-differentiated NETs are associated with low malignant potential and a favorable prognosis. Surgical resection is the preferred treatment, and long-term follow-up is necessary to monitor the patient's condition.

Extranodal NK/T-cell lymphoma (ENKTL) of the central nervous system (CNS) is very rare. We herein report a case of ENKTL originating from the CNS in a 79-year-old woman. The patient presented with episodic seizures, left-sided limb weakness, altered mental status, and dysarthria for more than 1 month. Radiological examination revealed a solitary mass in the (laterality) frontal lobe of the brain, which was surgically removed. Histopathology revealed a tumor showing diffuse growth of large anaplastic cells with multiple reniform nuclei, horseshoe nuclei, and doughnut-like nuclei. Immunohistochemically, the tumor cells were diffusely positive for CD3, CD30, Gramazyme B, and TIA1 and negative for ALK and CD56. It was almost misdiagnosed as ALK-negative anaplastic large cell lymphoma, but positivity for cytotoxic markers and EBER-ISH helped establish the diagnosis of ENKTL. To the best of our knowledge, this anaplastic variant of ENKTL has not been reported in the CNS. We present this case to describe an uncommon aggressive variant of ENKTL at CNS as a rare location with diagnostic pitfalls.

Almost all retinal pigment epithelial (RPE) adenocarcinomas are clinically diagnosed as choroidal melanomas. Retinal adenoma and adenocarcinoma appear black in color. A 63-year-old woman presented with progressive visual loss in her right eye with intermittent throbbing pain. A brownish pigmented choroidal mass was identified occupying the entire intraocular cavity with hemorrhagic foci. Histopathology revealed an infiltrative epithelial neoplasm with ill-defined glandular differentiation and moderate cytological atypia. Immunohistochemical staining with epithelial membrane antigen, cytokeratin 7, HMB-45, and S-100 favored a RPE origin of the lesion. RPE adenocarcinoma is exceedingly uncommon, but should be included in the differential diagnosis of pigmented intraocular tumors. Histopathology, combined with immunohistochemistry, is essential for accurate diagnosis.

Lately, STK11 adnexal tumors have been described in patients with Peutz-Jeghers syndrome (PJS), showing overlap with other adnexal tumors, especially female adnexal tumor of probable Wolffian origin (FATWO). To date, there is no documentation of this tumor from the Indian subcontinent. A 25-year-old female with mucocutaneous pigmented macules presented with acute abdominal pain along with a family history of surgical resection for gastrointestinal polyps in her mother and sister. Imaging revealed a well-defined, cystic right adnexal mass, distinct from the ovary, measuring 4.1 cm. Her colonoscopic examination was unremarkable. She underwent paraovarian cystectomy. Histopathological examination revealed a tumor composed of epithelioid cells arranged in various growth patterns with mild nuclear atypia. Immunohistochemically, the tumor cells were positive for pan-keratin, calretinin, CD10, FOXL2, and androgen receptor, the latter in 50% of the tumor cell nuclei. Initially, a diagnosis of FATWO was considered. Targeted next-generation sequencing revealed a pathogenic STK11 exon 4 frameshift mutation (c. 574dup), which was subsequently confirmed as a germline alteration on peripheral blood testing by Sanger sequencing, thereby establishing the diagnosis of an STK11 tumor with PJS. The differential diagnoses of this tumor and the judicious application of immunohistochemical stains, along with genetic testing (including high-throughput molecular testing in a clinical context) for an exact diagnosis, are discussed herein. A literature review including the molecular results of this rare tumor is also presented.

Paraquat, a toxic herbicide, continues to be widely used in developing nations despite restrictions and severe health risks. Several cases of poisoning have been reported due to intentional ingestion, producing dose-dependent clinical manifestations, chiefly targeting the lungs and kidneys. However, only a few cases have been reported in pregnancy. We report mortality due to paraquat-induced lung injury in a young pregnant woman, in whom the poisoning occurred following the ingestion of paraquat-contaminated soil as part of pregnancy-induced pica. The case underscores the critical need for early recognition and intervention.