MicroRNA 29a therapy for CEACAM6-expressing lung adenocarcinoma.

BACKGROUND: Non-coding microRNAs (miRNAs) play critical roles in tumor progression and hold great promise as therapeutic agents for multiple cancers. MicroRNA 29a (miR-29a) is a tumor suppressor miRNA that inhibits cancer cell growth and tumor progression in non-small cell lung cancer. Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), which plays an important role in lung cancer progression, has been identified as a target of miR-29a. Here, we evaluated the therapeutic efficacy of a peptide vector capable of delivering miR-29a intracellularly using the acidic tumor microenvironment in a lung adenocarcinoma xenograft mouse model. METHODS: A miRNA delivery vector was constructed by tethering the peptide nucleic acid form of miR-29a to a peptide with a low pH-induced transmembrane structure (pHLIP) to enable transport of the miRNAs across the plasma membrane. Tumor suppressive effects of pHLIP-miR29a on lung adenocarcinoma development in vivo were assessed using a BALB/c xenograft model injected with A549 cells. RESULTS: Incubation of A549 cells with pHLIP-miR-29a at an acidic pH downregulated endogenous CEACAM6 expression and reduced cell viability. Intravenous injection of the mice with pHLIP-miR-29a inhibited tumor growth by up to 18.1%. Intraperitoneal injection of cisplatin reduced tumor volume by 29.9%. Combined pHLIP-miR-29a + cisplatin treatment had an additive effect, reducing tumor volume up to 39.7%. CONCLUSIONS: Delivery of miR-29a to lung adenocarcinoma cells using a pHLIP-mediated method has therapeutic potential as a unique cancer treatment approach.

Antenatal sonographic features of persistent extrahepatic vitelline vein aneurysm confused with umbilical vein varix.

Background: The persistent vitelline vein is a portal venous system malformation arising during the embryonic period. These abnormal blood vessels frequently thrombose and can lead superior mesenteric vein obstruction or portal hypertension. Case report: We visualized a fetal intra-abdominal cystic mass with turbulent flow on prenatal ultrasound at 28 weeks' gestation. Initially diagnosed as an umbilical vein varix, it was later determined to be an extrahepatic persistent vitelline vein with an internal thrombus by postnatal ultrasound. It was successfully surgically excised. Conclusion: When an abnormal abdominal vascular structure near the umbilicus is found during prenatal ultrasonography, the persistent vitelline vein should be included in the differential diagnosis to allow prompt evaluation and treatment after birth.

Extra-articular tenosynovial giant cell tumor of diffuse type in the temporal area with brain parenchymal invasion: a case report.

Tenosynovial giant cell tumor of diffuse type is a locally aggressive neoplasm that most commonly arises in the lower extremities. Herein, we report for the first time a case of an extra-articular tenosynovial giant cell tumor of diffuse type in the temporal region with brain parenchymal invasion. Imaging studies revealed an intracranial expansile mass in the temporal bone without involvement of the temporomandibular joint. The unusual location of the tumor without involvement of the joint and the presence of brain parenchymal invasion made this case challenging to diagnose.

A Nationwide Study on HER2-low Breast Cancer in South Korea: Its Incidence of 2022 Real World Data and the Importance of Immunohistochemical Staining Protocols.

Purpose: Notable effectiveness of trastuzumab deruxtecan (T-DXd) in patients with HER2-low advanced breast cancer (BC) has focused pathologists' attention. We studied the incidence and clinicopathologic characteristics of HER2-low BC, and the effects of immunohistochemistry (IHC) associated factors on HER2 IHC results. Materials and Methods: The Breast Pathology Study Group of the Korean Society of Pathologists conducted a nationwide study using real-world data on HER2 status generated between January 2022 and December 2022. Information on HER2 IHC protocols at each participating institution was also collected. Results: Total 11,416 patients from twenty-five institutions included in this study. Of these patients, 40.7% (range: 6.0%-76.3%) were classified as HER2-zero, 41.7% (range: 10.5%-69.1%) as HER2-low, and 17.5% (range: 6.7%-34.0%) as HER2-positive. HER2-low tumors were associated with positive ER and PR statuses (p<0.001 and p<0.001, respectively). Antigen retrieval times (≥ 36 min vs. < 36 min) and antibody incubation times (≥ 12 min vs. < 12 min) affected on the frequency of HER2 IHC 1+ BC at institutions using the PATHWAY HER2 (4B5) IHC assay and BenchMark XT or Ultra staining instruments. Furthermore, discordant results between core needle biopsy (CNB) and subsequent resection specimen HER2 statuses were observed in 24.1% (787/3259) of the patients. Conclusion: The overall incidence of HER2-low BC in South Korea concurs with those reported in previously published studies. Significant inter-institutional differences in HER2 IHC protocols were observed, and it may have impact on HER2-low status. Thus, we recommend standardizing HER2 IHC conditions to ensure precise patient selection for targeted therapy.

Locally recurrent penile apocrine carcinoma initially diagnosed as metastatic adenocarcinoma of colon.

Apocrine carcinoma is a rare malignant adnexal neoplasm. The differential diagnosis between apocrine carcinoma and cutaneous metastasis is often difficult. Here, we report a case of locally recurrent penile apocrine carcinoma initially diagnosed as metastatic adenocarcinoma of the colon. A 75-year-old man with a history of surgical resection due to sigmoid colon cancer and penile metastasis two years prior to this study presented with a nodule at the left penile base. He underwent a wide local resection of the penile mass under a suggested preoperative diagnosis of extra-mammary Paget's disease (EMPD) associated with previous sigmoid colon cancer. However, the previously and currently resected penile masses were identified as primary apocrine carcinoma upon hematoxylin and eosin (H&E) staining and immunohistochemical staining. Although the incidence is extremely rare, both clinicians and pathologists should be alert to the possibility of synchronous double primary apocrine carcinoma in cancer patients with malignant cutaneous lesions.

Inflammatory myofibroblastic tumor of the urinary bladder with FN1­ALK gene fusion: A case report.

Inflammatory myofibroblastic tumors (IMTs), which are rare tumors, exhibit myofibroblastic differentiation, often with anaplastic lymphoma kinase (ALK) gene rearrangements. A subset of IMTs identified in the urinary tract have been shown to harbor a fibronectin 1 (FN1)-ALK gene fusion. In this case report, a case of an IMT with FN1-ALK fusion in the urinary bladder was presented, and its clinicopathological characteristics were reviewed. A 45-year-old female was referred to Chungbuk National University Hospital with gross hematuria. Cystoscopy revealed a solid mass in the bladder. The patient subsequently underwent transurethral resection of the lesion. The mass comprised stellate and spindled myofibroblastic cells that were arranged in loose fascicles, with a myxoid background and a mixed inflammatory infiltrate. Immunohistochemical analysis revealed that the tumor cells were positive for vimentin, cytokeratin AE1/AE3 and ALK, and focal-positive for desmin. Targeted next-generation sequencing was subsequently employed to identify the FN1-ALK fusion. To date, the patient has undergone outpatient follow-up for 18 months, with no signs of tumor recurrence. To conclude, in total, FN1 has been identified as an ALK fusion partner almost exclusively in cases of genitourinary IMTs [13 bladder IMTs (including the present case) and two uterine IMTs]. In the present case, the FN1-ALK fusion was found to involve ALK exon 19 and FN1 exon 23. By contrast, the majority of the other IMTs with an ALK fusion have involved ALK exon 20, whereas ALK fusion involving ALK exon 18 or 19 has been reported only in genitourinary IMTs. Therefore, the FN1-ALK fusion involving ALK exon 18 or 19 may be specific to a subset of IMTs arising in the urinary bladder.

Diagnostic proficiency test using digital cytopathology and comparative assessment of whole slide images of cytologic samples for quality assurance program in Korea.

BACKGROUND: The Korean Society for Cytopathology introduced a digital proficiency test (PT) in 2021. However, many doubtful opinions remain on whether digitally scanned images can satisfactorily present subtle differences in the nuclear features and chromatin patterns of cytological samples. METHODS: We prepared 30 whole-slide images (WSIs) from the conventional PT archive by a selection process for digital PT. Digital and conventional PT were performed in parallel for volunteer institutes, and the results were compared using feedback. To assess the quality of cytological assessment WSIs, 12 slides were collected and scanned using five different scanners, with four cytopathologists evaluating image quality through a questionnaire. RESULTS: Among the 215 institutes, 108 and 107 participated in glass and digital PT, respectively. No significant difference was noted in category C (major discordance), although the number of discordant cases was slightly higher in the digital PT group. Leica, 3DHistech Pannoramic 250 Flash, and Hamamatsu NanoZoomer 360 systems showed comparable results in terms of image quality, feature presentation, and error rates for most cytological samples. Overall satisfaction was observed with the general convenience and image quality of digital PT. CONCLUSIONS: As three-dimensional clusters are common and nuclear/chromatin features are critical for cytological interpretation, careful selection of scanners and optimal conditions are mandatory for the successful establishment of digital quality assurance programs in cytology.

Histologic Changes in Non-Small Cell Lung Cancer under Various Treatments: A Comparison of Histology and Mutation Status in Serial Samples.

PURPOSE: Histologic change is a resistant mechanism in lung cancer. The most common histological change is the switch from adenocarcinoma (AdenoCa) to small cell carcinoma (SCC) against to tyrosine kinase inhibitors (TKI). However, it is not clear whether other treatment modalities are involved in the histologic changes. MATERIALS AND METHODS: We investigated histological changes in eight cases, after various treatments, and compared the molecular profiles between primary tumors and changed tumors using exome sequencing where tissue was available. RESULTS: Three cases of AdenoCa that were changed into SCC retained the initial mutations after TKI and/or surgical treatment. After treatment with TKI and immunotherapy, an EGFR (epidermal growth factor receptor)-mutant AdenoCa changed to squamous cell carcinoma (SqCa). SqCa in a patient treated with surgery was changed into combined AdenoCa and SqCa. These two cases showed the same genetic variations between the two distinct non-small cell carcinomas (NSCC). Three patients experienced two histologic changes, which the changed tumors returned to its original subtype or changed to a combined tumor after treatments. Four cases showed combined histology in the first or second change. CONCLUSION: The histology of NSCC can be changed to a single pattern or combined subtypes after various treatment modalities, and the phenotypic changes seem not fixed. Therefore, additional morphologic changes may occur regardless of their genetic status and types of treatments. To refine the new treatment strategy, consecutive repeated biopsies in progressive disease or recurrent tumor are necessary.

FTS (fused toes homolog) a novel oncoprotein involved in uterine cervical carcinogenesis and a potential diagnostic marker for cervical cancer.

The high incidence and fatality rate of uterine cervical cancer warrant effective diagnostic and therapeutic target identification for this disease. Here, we have found a novel oncoprotein FTS (Fused Toes Homolog), which is involved in cervical cancer pathogenesis. Immunohistochemical analysis of human cervical biopsy samples revealed that the expression of FTS is absent in normal cervical epithelium but progressively overexpressed in human cervical intraneoplastic lesions (CIN-I to CIN-III), this characteristic phenomenon put this protein, a potential diagnostic marker for the screening of early neoplastic changes of cervix. Using FTS-specific small hairpin RNA (shRNA) in cervical cancer cells, we determined a specific role for FTS protein in, cervical neoplasia. Targeted stable knock down of FTS in HeLa cells led to the growth inhibition, cell-cycle arrest, and apoptosis with concurrent increase in p21 protein. FTS effectively represses the p21 mRNA expression in dual luciferase assay which indicates that p21 is transcriptionally regulated by this oncoprotein which in turn affect the regular cell-cycle process and its components. Consistent with this we found a reciprocal association between these proteins in early cervical neoplastic tissues. These data unraveled the involvement of new oncoprotein FTS in cervical cancer which plays a central role in carcinogenesis. Targeted inhibition of FTS lead to the shutdown of key elemental characteristics of cervical cancer and could lead to an effective therapeutic strategy for cervical cancer.

Positive response to trastuzumab in a case of HER2-overexpressing metastatic gastric cancer that presented as severe thrombocytopenia.

BACKGROUND: Trastuzumab, a humanized monoclonal antibody directed against human epidermal growth factor receptor 2 (HER2), has been shown to be active against metastatic gastric cancers that overexpress HER2. CASE REPORT: A 47-year-old man presented with a headache and visual disturbance. He was subsequently found to have an intracranial hemorrhage. Laboratory testing showed severe thrombocytopenia, and a bone marrow biopsy revealed aggregates of malignant tumor cells. Endoscopic biopsy of an ulcerative lesion of the gastric antrum confirmed signet ring cell carcinoma based on the results of H&E staining. Immunohistochemistry of the tumor cells revealed HER2 overexpression with an intensity of 3+, and silver in situ hybridization showed HER2 gene amplification. The patient was treated with trastuzumab because of the presence of severe thrombocytopenia. After 2 months of trastuzumab therapy, gastric wall thickening and ascites were diminished and thrombocytopenia was markedly improved. Trastuzumab was continued for an additional 3 months. CONCLUSION: This is the first report of a positive response to trastuzumab in a patient with HER2-overexpressing metastatic gastric cancer that was accompanied by bone marrow involvement and severe thrombocytopenia. This finding is of considerable relevance for difficult cases of metastatic gastric cancer that preclude the administration of aggressive antineoplastic regimens.

A multicenter study of interobserver variability in pathologic diagnosis of papillary breast lesions on core needle biopsy with WHO classification.

BACKGROUND: Papillary breast lesions (PBLs) comprise diverse entities from benign and atypical lesions to malignant tumors. Although PBLs are characterized by a papillary growth pattern, it is challenging to achieve high diagnostic accuracy and reproducibility. Thus, we investigated the diagnostic reproducibility of PBLs in core needle biopsy (CNB) specimens with World Health Organization (WHO) classification. METHODS: Diagnostic reproducibility was assessed using interobserver variability (kappa value, κ) and agreement rate in the pathologic diagnosis of 60 PBL cases on CNB among 20 breast pathologists affiliated with 20 medical institutions in Korea. This analysis was performed using hematoxylin and eosin (H&E) staining and immunohistochemical (IHC) staining for cytokeratin 5 (CK5) and p63. The pathologic diagnosis of PBLs was based on WHO classification, which was used to establish simple classifications (4-tier, 3-tier, and 2-tier). RESULTS: On WHO classification, H&E staining exhibited 'fair agreement' (κ = 0.21) with a 47.0% agreement rate. Simple classifications presented improvement in interobserver variability and agreement rate. IHC staining increased the kappa value and agreement rate in all the classifications. Despite IHC staining, the encapsulated/solid papillary carcinoma (EPC/SPC) subgroup (κ = 0.16) exhibited lower agreement compared to the non-EPC/SPC subgroup (κ = 0.35) with WHO classification, which was similar to the results of any other classification systems. CONCLUSIONS: Although the use of IHC staining for CK5 and p63 increased the diagnostic agreement of PBLs in CNB specimens, WHO classification exhibited a higher discordance rate compared to any other classifications. Therefore, this result warrants further intensive consensus studies to improve the diagnostic reproducibility of PBLs with WHO classification.

Expression of sonic hedgehog signaling molecules in normal, hyperplastic and carcinomatous endometrium.

The aim of the present study was to determine the expression profile of the hedgehog (Hh) signaling molecules in normal, hyperplastic, and carcinomatous uterine endometrium. For this purpose, 271 endometrial tissue samples, (62 of normal endometrium, 127 of endometrial hyperplasias, and 82 endometrial adenocarcinomas) were studied using antibodies recognizing Hh-related signaling proteins, such as, sonic hedgehog (Shh), Patched (PTCH), Smoothened (Smo), Suppressor of fused [Su(Fu)], Gli-1, Gli-2, and Gli-3 by immunohistochemistry. The mRNA expression of these molecules was also assessed on reverse transcription-polymerase chain reaction. In the normal endometrium, the expression of Hh signaling molecules was generally downregulated except for Su(Fu), Gli-2, and Shh. In particular, the expression of both PTCH and Smo was very low or almost absent. Overall expression of Hh signaling molecules increased in hyperplastic endometrium; in particular, PTCH and Smo were significantly highly expressed in complex and atypical hyperplasia. In carcinoma samples extensive alterations were observed in the expression pattern of the signaling molecules. Nuclear Gli-2, cytoplasmic Gli-3, and Su(Fu) were overexpressed, whereas Shh, PTCH, and Smo expression were significantly reduced compared with the hyperplastic endometrium. The results suggest that the alteration of Hh signaling may be implicated in tumorigenesis of the endometrium.

Clinicopathological characteristics of costal hemangiomas: a case report and literature review.

Bone hemangioma accounts for approximately 1% of all bone neoplasms and commonly occurs in the vertebral body and skull. However, costal hemangiomas are extremely rare. We herein present a case involving a 52-year-old woman with a hemangioma in the third rib and review 29 cases of rib hemangiomas available in the literature. Rib hemangioma mainly affects women in their 50s and has expansile osteolytic features in radiographs and a weak maximum standardized uptake value in 18F-fluorodeoxyglucose positron emission tomography images. When these findings are displayed, clinicians should include rib hemangioma as a differential diagnosis and consider avoidance of preoperative biopsy because of the risk of life-threatening bleeding.

Therapeutic Effect of pHLIP-mediated CEACAM6 Gene Silencing in Lung Adenocarcinoma.

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) plays an important role in lung cancer progression. Here, we examined the therapeutic efficacy of CEACAM6 gene silencing using an siRNA delivery platform targeting the acidic tumour microenvironment in a lung adenocarcinoma xenograft mouse model. An siRNA delivery vector was constructed by tethering the peptide nucleic acid form of an siRNA targeting CEACAM6 (siCEACAM6) to a peptide with a low pH-induced transmembrane structure (pHLIP) to transport siRNAs across the plasma membrane. Specific binding of the pHLIP-siCEACAM6 conjugate to A549 lung adenocarcinoma cells at low pH was demonstrated by flow cytometry. A549 cells incubated with pHLIP-siCEACAM6 at an acidic pH showed downregulated expression of endogenous CEACAM6 protein and reduced cell viability. The in vivo tumour-suppressing effects of pHLIP-siCEACAM6 in lung adenocarcinoma were assessed in a xenograft model generated by injecting BALB/c nude mice with A549 cells. pHLIP-siCEACAM6 treatment alone resulted in tumour growth inhibition of up to 35.5%. When combined with cisplatin treatment, pHLIP-siCEACAM6 markedly enhanced tumour growth inhibition by up to 47%. In conclusion, the delivery of siCEACAM6 to lung adenocarcinoma using the pHLIP peptide has therapeutic potential as a unique cancer treatment approach.

Interstitial Nephritis Caused by Anorexia Nervosa in Young Male; A Case Report and Literature Review.

Severe eating disorders characterized by repetitive episodes of purging and vomiting can occasionally trigger acute kidney injury. However, interstitial nephritis induced by episodes of repeated vomiting has rarely been reported, and the pathophysiology of this entity remains unknown. A 26-year-old man was admitted to our hospital because of known hypokalemia. His serum electrolyte profile showed: sodium 133 mEq/L, potassium 2.6 mEq/L, chloride 72 mEq/L, total carbon dioxide 50 mEq/L, blood urea nitrogen/creatinine ratio (BUN/Cr) 21.9/1.98 mg/dL, and magnesium 2.0 mg/dL. Arterial blood gas analysis showed: pH 7.557, partial pressure of carbon dioxide 65.8 mmHg, and bicarbonate 58.5 mEq/L. His urinary potassium concentration was 73.2 mEq/L, and Cr was 111 mg/dL. Renal biopsy revealed acute tubular necrosis and tubulointerstitial nephritis with a few shrunken glomeruli. Repeated psychogenic vomiting may precipitate acute kidney injury and interstitial nephritis secondary to volume depletion and hypokalemia. Serum electrolyte levels and renal function should be carefully monitored in patients diagnosed with eating disorders to prevent tubular ischemia and interstitial nephritis.

Large Cell Neuroendocrine Carcinoma of the Colon With Carcinomatosis Peritonei.

Colorectal large-cell neuroendocrine carcinomas (NECs) are extremely rare and have very poor prognosis compared to adenocarcinomas. A 74-year-old man presented with abdominal pain, diarrhea and hematochezia. The histopathologic report of colonoscopic biopsy performed at a local clinic was a poorly differentiated carcinoma. An abdominopelvic computed scan revealed irregularly enhanced wall thickening at the sigmoid colon with regional fat stranding and lymphnode enlargement. He underwent a laparoscopic high anterior resection with selective peritonectomy for peritoneal carcinomatosis, intraoperative peritoneal irrigation chemotherapy, and early postoperative intraperitoneal chemotherapy for 5 days. The tumor had a high proliferation rate (mitotic count > 50/10 HPFs and 90% of the Ki-67 index) and lymph-node metastases had occurred. On immunohistochemistry, the tumor cells expressed CD56 and synaptophysin. Large-cell NEC was confirmed. Systemic chemotherapy with cisplatin/etoposide was done. The patient is still alive after 3 years with no evidence of recurrence.

Diagnostic benefits of the combined use of liquid-based cytology, cell block, and carcinoembryonic antigen immunocytochemistry in malignant pleural effusion.

BACKGROUND: Malignant pleural effusion (MPE) is a common complication of cancer cell metastasis to the pleura. Discrimination between MPE and benign pleural effusion is necessary to design treatment strategies. Cytology is important for the diagnosis of MPE. Carcinoembryonic antigen (CEA) is an epithelial biomarker with a strong staining pattern in adenocarcinomas. Here, the diagnostic performances of liquid-based cytology (LBC), cell block (CB) preparation, and CEA immunostaining for the detection of malignancy in effusion cytology were compared in a large case series. METHODS: In a single institution, 1,014 cytology samples from 862 patients were retrospectively collected and reviewed between January 2013 and November 2015. Ethanol-fixed, paraffin embedded CB of pleural effusions was analyzed by CEA immunostaining. Diagnostic values were compared among LBC, CB, CEA immunostaining, and the combination of two methods. RESULTS: The sensitivity and specificity of the CB preparation were 94.3% and 98.7%, respectively, compared with 81.3% and 99.4% for LBC preparations, respectively. Combination of LBC and CB increased sensitivity by 98.3%. Although the accuracy of CEA staining itself was moderate (sensitivity, 89.8%), the combined use of CB and CEA tumor marker increased the detection rate of malignancy (sensitivity, 100%; specificity, 100%), compared with that of cytology (LBC or CB) alone. CONCLUSIONS: The sensitivity and specificity for the diagnosis of MPE could be improved by integrating the CB and CEA staining into LBC in routine clinical practice to improve diagnostic accuracy.

Comparison of liquid-based cytology (CellPrepPlus) and conventional smears in pancreaticobiliary disease.

BACKGROUND/AIMS: Endoscopic ultrasound-guided fine needle aspiration (EUSFNA) and brushing cytology are used worldwide to diagnose pancreatic and biliary malignant tumors. Liquid-based cytology (LBC) has been developed and it is currently used to overcome the limitations of conventional smears (CS). In this study, the authors aimed to compare the diagnostic value of the CellPrepPlus (CP; Biodyne) LBC method with CS in samples obtained using EUS-FNA and brushing cytology. METHODS: This study prospectively enrolled 75 patients with pancreatic or biliary lesions from June 2012 to October 2013. For cytological analyses, including inadequate specimens, benign and atypical were further classified into benign, and suspicious and malignant were subcategorized as malignant. Sensitivity, specificity, accuracy, and positive predictive values (PPV) and negative predictive values (NPV) were evaluated. RESULTS: In the EUS-FNA based cytological analysis of pancreatic specimens, CP had a sensitivity of 60.7%; specificity, 100%; accuracy, 77.1%; PPV, 100%; and NPV, 64.5%. CS had a sensitivity of 85.7%; specificity, 100%; accuracy, 91.7%; PPV, 100%; and NPV, 83.3%. In the brushing cytology based analysis of biliary specimens, CP had sensitivity of 53.1%; specificity, 100%; accuracy, 54.5%; PPV, 100%; and NPV, 6.3%. CS had a sensitivity of 78.1%; specificity, 100%; accuracy, 78.8%; PPV, 100%; and NPV, 12.5%. CONCLUSION: Our study found that CP had a lower sensitivity because of low cellularity compared with CS. Therefore, CP (LBC) has a lower diagnostic accuracy for pancreatic EUS-FNA based and biliary brush cytology based analyses compared with CS.

Primary merkel cell carcinoma of the oral mucosa: a case report with review of literature.

We present a case of primary Merkel cell carcinoma in the oral mucosa of a 60-year-old man. The patient underwent incisional biopsy of the tumor. Histologically, the tumor was composed of small monotonous cells in a solid sheet-like and single-cell row growth pattern. Immunohistochemically, tumor cells were positive for pan-cytokeratin, CD56, and synaptophysin, and negative for leukocyte common antigen, vimentin, S-100 protein, HMB-45, and thyroid transcription factor 1. Cytokeratin 20 staining showed a paranuclear dot-like pattern in tumor cells. Therefore, the diagnosis of Merkel cell carcinoma was made. The patient received chemotherapy with etoposide and cisplatin followed by 62 Gy radiation in 31 fractions over seven weeks. Follow-up brain CT scans after three and five months showed complete remission of the mass and enlarged lymph node. He is currently doing well with no evidence of recurrence. The present case is the first report of Merkel cell carcinoma arising in the buccal vestibule.The patient is currently doing well with no evidence of recurrence at six months.