Background/Aim: Appendiceal neuroendocrine tumors (ANETs) are the most prevalent type of appendiceal neoplasm and the fifth most common neuroendocrine tumor in the gastrointestinal tract. In this study, we described the clinicopathological features of patients with ANET. Patients and Methods: We reviewed the clinicopathological findings and histopathological reports of six patients diagnosed with ANET between January 2014 and December 2023 at Korea University Medical Center, Anam Hospital. Results: Six cases, comprising three males and three females, were diagnosed during procedures for lower abdominal pain or other medical reasons. Most tumors were less than 1 cm in size and located at the tip of the appendix. One patient had a large tumor (4.1 cm) with lymph node metastasis. Four tumors extended to the muscularis propria, whereas two infiltrated the subserosal soft tissue. The tumor cells exhibited a typical trabecular and nested pattern with monotonous round or oval nuclei. All patients had a mitotic count of less than 2 per 10 high-power fields and a Ki-67 labeling index of less than 1%, classifying them as having G1 well-differentiated tumors. Immunohistochemical staining showed that all cases were positive for CD56 and synaptophysin, and four were positive for chromogranin A. No recurrence or distant metastasis was observed during follow-up. Conclusion: ANETs are relatively uncommon and mostly benign in terms of prognosis. Because of their malignant potential, meticulous examination of appendectomy specimens is warranted to identify the presence of ANETs.

Background/Objectives: Mutations in RAS/RAF are common in colorectal cancer (CRC) and play a pivotal role in guiding treatment selection. With the recent advent of immunotherapy, microsatellite (MSI) status, tumor mutation burden (TMB), and POLE mutations, particularly those leading to high TMB, have gained importance in CRC. This study aimed to examine the clinicopathological characteristics of patients with CRC with POLE mutations. Methods: We identified POLE mutations in patients with colorectal cancer who had available next-generation sequencing (NGS) results from a single institute in Korea. RAS/RAF status, MSI status, and TMB were evaluated, and based on the TMB results, patients with POLE mutations were classified as having either pathogenic or non-pathogenic mutations. After excluding non-Korean patients, we compared the groups based on the presence of pathogenic POLE mutations. Results: Five POLE mutations (A456P, P286R, R1111W, R609W, and V922I) were identified. Only A456P and P286R were associated with an exceptionally high TMB, resulting in two patients (1.1%) being categorized as having pathogenic POLE. The POLE-mutant group showed an extremely high TMB and tended to include younger patients. Among the two pathogenic cases, one showed poor histological differentiation, and the tumors were split between the right and left colons (one in each). Conclusions: CRC with POLE mutations tend to exhibit TMB-high, occur in younger patients, localize to the right colon, and display poor histological differentiation. Given that POLE mutations can serve as indicators for immunotherapy, recognizing these mutations is of clinical importance.

Background/Aim: Vascular invasion (VI) in colorectal carcinoma (CRC) is an independent prognostic feature and a high-risk indicator for adjuvant chemotherapy in stage II CRC. This study evaluated the effect of elastic staining on VI detection. Patients and Methods: The VI was assessed using elastic staining in 154 patients with CRC. Based on hematoxylin and eosin (H&E) staining, cases were classified into three groups: absent (n=80), equivocal (n=23), and suspected (n=51). Two sections per case were evaluated for VI using elastic staining, and the presence of VI on one or both slides was confirmed. Finally, the correlation between the VI and other clinicopathological factors was analyzed. Results: The overall detection rate of VI using elastic staining was 67/154 (51.4%). VI was detected in 17/80 (21.3%), 3/23 (13.0 %), and 47/51 (92.2%) patients in the absent, equivocal, and suspected groups, respectively. VI was detected in both sections of the elastic staining slides in 28 cases, and in only one section in 38 cases. The VI was significantly associated with perineural invasion, M stage, and synchronous metastasis. Conclusion: VI detection using H&E staining alone is not reliable, emphasizing the importance of elastic staining in improving VI detection. Therefore, we recommend the incorporation of elastic staining into routine pathological practice for all pT3 and pT4 CRC cases.