Although the understanding of appendiceal mucinous neoplasms (AMNs) and their relationship with disseminated peritoneal mucinous disease have advanced, the diagnosis, classification, and treatment of AMNs are still confusing for pathologists and clinicians. The Gastrointestinal Pathology Study Group of the Korean Society of Pathologists (GPSG-KSP) proposed a multicenter study and held a workshop for the “Standardization of the Pathologic Diagnosis of the Appendiceal Mucinous Neoplasm” to overcome the controversy and potential conflicts. The present article is focused on the diagnostic criteria, terminologies, tumor grading, pathologic staging, biologic behavior, treatment, and prognosis of AMNs and disseminated peritoneal mucinous disease. In addition, GPSG-KSP proposes a checklist of standard data elements of appendiceal epithelial neoplasms to standardize pathologic diagnosis. We hope the present article will provide pathologists with updated knowledge on how to handle and diagnose AMNs and disseminated peritoneal mucinous disease.

Most pancreatic carcinoma is ductal adenocarcinoma. Primary pancreatic clear cell carcinomas composed almost entirely of clear tumor cells are very rare. We present a case of a 72-year-old man with a pancreatic mass, which was detected on abdominal computed tomography (CT). He had no symptoms and no abnormal findings on physical examination; however, he had a history of hepatitis B, hepatitis C, and hepatocellular carcinoma. He had received anti-viral treatment and radiofrequency ablation twice until 2 years prior. One year prior, follow-up contrast-enhanced abdominal CT revealed a newly developed pancreatic mass. Laparoscopic radical antegrade modular pancreato-splenectomy was performed. An ill-defined white-to-tan firm solid mass was observed in the pancreas, approximately 4.3 cm in diameter. The tumor cells showed >95% clear cell features, with a large round to oval nuclei and abundant clear cytoplasms, and well-defined cell membranes. Immunohistochemical staining revealed that the tumor cells were positive for cytokeratin 7, cytokeratin 19, HNF-1β, MUC-1, and p53. We excluded the possibility of metastatic clear renal cell carcinoma, neuroendocrine carcinoma, perivascular epithelioid cell tumor, malignant melanoma, and sarcoma because of the negativity for vimentin, chromogranin, synaptophysin, and HMB45. Consequently, he was diagnosed as having primary clear cell carcinoma of the pancreas and was treated with postoperative radiotherapy. Two months later, abdominal CT was suspicious for local recurrence at the resection margin. Additional adjuvant FOLFIRINOX chemotherapy was carried out 12 times. The patient is still alive after his third radiofrequency ablation for the newly-developed hepatic mass. Immunohistochemical staining for MUC-1 and HNF-1β, as well as histologic feature is very helpful for the diagnosis of primary pancreatic clear cell carcinoma with imaging methods for metastasis exclusion.

An inflammatory pseudotumor is a benign disease characterized by tumor-like lesions consisting of inflammatory cells including plasma cells and fibrous tissue. Recently, some inflammatory pseudotumor cases proved to be a form of Immunoglobulin G4-related disease (IgG4-RD). This novel clinical entity, recognized as a fibroinflammatory condition, is characterized by lymphoplasmacytic infiltration with a predominance of IgG4-positive plasma cells, storiform fibrosis, and often elevated serum IgG4 concentrations. We report a case of IgG4-RD in the form of an inflammatory pseudotumor in the liver with combined sclerosing cholangitis. We recommend that for diagnosing IgG4-RD accurately, it is important to obtain adequate tissue samples and follow-up the lesion in clinical practice.

In patients with thyroid nodules, if the cervical lymph nodes gradually enlarge, a histological confirmation is required to rule out malignancy. Here is a case of benign intranodal thyroid tissue with cystic changes resembling lymph node metastasis of a papillary thyroid carcinoma. A 47-year-old man received ethanol sclerotherapy because of repeated enlargement of the thyroid gland 2 years prior to presentation. Subsequently, the patient underwent abscess removal from the deep neck and partial lobectomy of the attached left thyroid gland. Two months before the visit, extensive cervical lymphadenopathy was detected on ultrasonography (US) and computed tomography (CT). Total thyroidectomy and cervical lymph node dissection were performed to differentiate between metastatic papillary carcinoma of the thyroid gland and benign thyroid inclusions. Microscopic examination revealed multiple variable-sized nodules of benign thyroid follicles with cystic changes in both thyroid glands and bilateral cervical lymph nodes. An occult papillary microcarcinoma strongly positive for HBME-1 was also observed in the left thyroid lobe. However, the benign intranodal thyroid tissue was negative in both the real-time PCR-based BRAF V600E mutation test and HBME-1 immunohistochemical stain. Similarly, benign intranodal thyroid tissue can be enlarged by multiple cystic changes in a large number of lymph nodes along the neck node chain. For the differentiation of metastatic thyroid papillary carcinoma, real-time PCR-based BRAF V600E mutation test and HBME-1 immunohistochemical staining in addition to histological examination are helpful.

Fexuprazan, a potassium‐competitive acid blocker, is increasingly used for the treatment of gastroesophageal reflux disease in South Korea. While generally well tolerated, data regarding its hepatotoxic potential are scarce. We report a case of idiosyncratic drug‐induced liver injury in a 61‐year‐old woman following 2 months of fexuprazan therapy. She presented with fatigue and elevated liver enzymes, and liver biopsy demonstrated single‐cell necrosis, interface hepatitis and eosinophilic infiltration—features consistent with drug‐induced liver injury. Her liver function normalized after drug discontinuation. However, approximately 20 months later, the patient experienced a recurrence of liver injury after unintentionally being prescribed fexuprazan again. The second episode showed similar biochemical and histological features, fulfilling Hy's law criteria and increasing the RUCAM score from probable to highly probable . Pharmacokinetic analysis during the first episode revealed a prolonged elimination half‐life, suggestive of impaired metabolism during active hepatic injury. Pharmacogenetic testing revealed a cytochrome P450 enzyme 2C19 poor metabolizer genotype, although its clinical relevance was limited in this case. This report highlights a rare but reproducible adverse drug reaction to fexuprazan and emphasizes the importance of thorough drug history and postmarketing surveillance. To our knowledge, this is the first report of recurrent fexuprazan‐induced liver injury confirmed by unintentional re‐exposure.

Rationale: Adrenal mixed corticomedullary tumors (MCMTs) are single tumor masses composed of an intimately admixed population of both adrenal cortical cells and medullary components. Most medullary tumor components are pheochromocytomas; however, MCMTs composed of ganglioneuroma and adrenal cortical adenoma are extremely rare. The current case is a rare case of adrenal MCMT composed of ganglioneuroma and adrenal cortical adenoma with primary aldosteronism. Patient concerns: A 49-year-old male was admitted because of hypokalemia and an adrenal mass. He was diagnosed with hypertension in his 20s and was taking blood pressure medications. Diagnosis: Plasma aldosterone concentration 376.5 pg/dL (normal 37.8~233.0 pg/mL) and potassium 2.8 mmol/L (normal 3.4~4.9 mmol/L) were detected. The aldosterone-to-renin ratio [the ratio of plasma aldosterone concentration (ng/dL) to PRA (ng/mL/hour)] was 38. The saline loading test showed that serum aldosterone (49.4 ng/dL) was not suppressed, compared with the basal level (28.4 ng/dL). The adrenal venous sampling test showed that the aldosterone level markedly increased to 1521.2 pg/mL. Abdominal computed tomography revealed an enlarged relatively well-circumscribed multinodular mass (35 × 13 × 30 mm) in the right adrenal gland. Interventions: Laparoscopic right adrenalectomy was performed under the clinical diagnosis of a functioning adrenal cortical adenoma. Outcomes: After laparoscopic right adrenalectomy, the serum aldosterone and renin levels returned to normal. The patient maintained a normal aldosterone level without recurrence for 16 months. Lessons: Adrenal MCMTs of the ganglioneuroma and cortical adenomas in the ipsilateral adrenal gland are extremely rare. Adrenal MCMTs exhibit benign clinical behavior, with no metastasis or death due to the tumor. With the development of diagnostic imaging technology, it is possible to identify mixed tumors. However, surgical resection of adrenal gland is a common treatment and a final diagnosis should be made based on the pathological results after surgery. Because this is to rule out the occurrence of rare malignant tumors and confirm the pattern of mixed tumors.