5-Hydroxymethylcytosine (5-hmC) loss is a marker of malignancy in biliary neoplasms.

OBJECTIVES: Adenocarcinomas of the biliary tract frequently present diagnostic challenges because of their histologic overlap with benign and preinvasive lesions. The molecular profiles of biliary adenocarcinomas vary by anatomical location. Variations in IDH1/2, common in intrahepatic cholangiocarcinoma, can lead to defective production of 5-hydroxymethylcytosine (5-hmC). Limited ancillary studies are available for biliary adenocarcinomas, and loss of 5-hmC staining could serve as a helpful ancillary diagnostic tool for biliary tract malignancies. METHODS: We evaluated 93 cases-20 benign biliary lesions, 15 preinvasive biliary neoplasms, 46 invasive biliary carcinomas, and 12 pancreatic adenocarcinomas-for 5-hmC staining. Preoperative biopsies from 16 cases of biliary carcinoma were also stained. Sixteen nonneoplastic/reactive bile duct biopsies served as controls. RESULTS: Loss of 5-hmC was seen in 41 of 46 (89.1%) biliary malignancies vs 0 of 20 benign tumors (P < .001), for a sensitivity and specificity of 89.1% and 100%, respectively. Intrahepatic cholangiocarcinoma showed loss of 5-hmC in 11 of 13 (84.6%) cases, similar to the 30 of 33 (90.9%) cases in other biliary adenocarcinomas (P = .61). Similarly, 5-hmC loss was more frequent in distal bile duct adenocarcinomas than in pancreatic ductal adenocarcinomas, at 15 of 17 (88.2%) vs 4 of 12 (33.3%), respectively (P = .0045). There was no difference in the frequency of 5-hmC loss in patients that received neoadjuvant therapy vs those who did not (90.9% vs 88.6%, P > .99). 5-hmC immunohistochemistry in preoperative biopsies was concordant with the resection specimen in 81.3% (13/16) of cases. CONCLUSIONS: Loss of 5-hmC is not unique to intrahepatic cholangiocarcinoma among biliary carcinomas, but is a useful diagnostic marker differentiating malignancies of the biliary tree from benign mimics.

Proliferative Clonal T-Cell Infiltrate Mimicking a Cutaneous T-Cell Lymphoma Arising in Active Regression of Melanoma.

ABSTRACT: Complete melanoma regression is an uncommon phenomenon involving a complex interplay of the tumor microenvironment and host immune response. We report a case of an 84-year-old woman with a history of colon and breast cancers who presented with a right forearm tumor, which was found to be a nodular melanoma; focal features of regression were noted in the biopsy. Approximately 6 weeks later, surgical resection of the site revealed no gross evidence of tumor, and histologic sections showed an extensive lymphoid infiltrate with prominent epidermotropism. Rare residual melanoma cells were present in the dermis, best visualized on immunohistochemical stains. T cells predominated in the infiltrate with an inverted CD4:CD8 ratio at approximately 1:2. There was no appreciable loss of pan‒T-cell antigens. T-cell receptor beta and gamma gene rearrangements were performed by polymerase chain reaction and demonstrated clonality in each assay. Although a synchronous cutaneous T-cell lymphoma was considered, the overall clinicopathologic features are more in line with an exaggerated host immune response leading to near complete regression of the tumor.

Indolent CD8+ primary cutaneous T-cell lymphoma involving the eyelid of an adolescent.

Primary cutaneous acral CD8+ T-cell lymphoma (PCACTL) is currently a provisional entity defined as a rare cutaneous proliferation of atypical CD8+ lymphocytes that preferentially involves acral sites and has a good prognosis. We present a case of primary cutaneous CD8+ T-cell lymphoma involving the eyelid of an adolescent male. The case shares features with PCACTL, including indolent clinical behavior and expression of CD68 in a Golgi-associated dot-like pattern; however, other features differ significantly from PCACTL as currently defined by the World Health Organization (WHO). These features include ulceration, expression of CD56, granzyme B, and perforin, and a high proliferative index. Given these discrepancies, our case is currently best classified as a CD8+ primary cutaneous peripheral T-cell lymphoma, not otherwise specified. We review the differential diagnosis for this case and suggest expanding the definition of PCACTL.

Diminished expression of 5hmc in Reed-Sternberg cells in classical Hodgkin lymphoma is a common epigenetic marker.

Loss of the epigenetic marker 5-hydroxymethylcytosine (5hmC) has been demonstrated in a variety of neoplasms. Several recent studies have shown epigenetic alteration in Classical Hodgkin lymphoma (CHL), which may impact treatment. We demonstrate near universal depletion of 5hmC in the neoplastic Hodgkin Reed-Sternberg (H/RS) cells in all cases of CHL (49/49). We hypothesized that the addition of vitamin C-a cofactor for the ten-eleven translocation (TET) enzymes which oxidize 5-methylcytosine (5mC) to 5hmC - may replenish levels of 5hmC. The CHL cell line L428 was grown in optimal conditions and then subjected to vitamin C treatment, which demonstrated reduced cell viability as well as caspase activation and increased concentration of 5hmC. A more detailed understanding of the epigenetic landscape of CHL may help guide future therapies.

Diagnostic utility of dual 5-hydroxymethylcytosine/Melan-A immunohistochemistry in differentiating nodal nevus from metastatic melanoma: An effective first-line test for the workup of sentinel lymph node specimen.

BACKGROUND: Distinguishing benign nodal nevus from metastatic melanoma can be diagnostically challenging, with important clinical consequences. Recently, the loss of epigenetic marker, 5-hydroxymethylcytosine (5-hmC) expression by immunohistochemistry has been found in melanomas and atypical melanocytic neoplasms. METHODS: About 41 metastatic melanomas and 20 nodal nevi were retrieved. Nuclear 5-hmC (brown) and cytoplasmic Melan-A Red (red) double immunohistochemical staining was performed. RESULTS: Total or partial loss of nuclear expression of 5-hmC was noted in 40/41 metastatic melanomas; these tumor cells were strongly positive for Melan-A Red, except in one case of desmoplastic melanoma. All cases of nodal nevus showed uniformly retained nuclear expression of 5-hmC accompanied by strong Melan-A Red cytoplasmic staining. In two cases containing both nodal nevus and metastatic melanoma, all tumor cells were positive for Melan-A Red, but a nuclear expression of 5-hmC was selectively absent only in the melanoma tumor cells. CONCLUSION: Dual 5-hmC/Melan-A Red immunohistochemistry is highly specific in distinguishing nodal nevus from metastatic melanoma. Our protocol for brown and red chromogens used in this study provides excellent color contrast and is easy to interpret. Furthermore, this dual staining method allows the preservation of limited tumor tissue, which could be used for potential molecular studies.

Primary Visceral Merkel Cell Carcinoma: A Case Report and Review of the Literature.

A 63-year-old white man with no significant previous medical or surgical history presented with painless jaundice after 3 weeks of dark urine, yellow stools, and a 9-pound weight loss. Bilirubin, aspartate transaminase, alanine transaminase, and alkaline phosphatase were elevated, and a computed tomography scan detected a 10-cm, ill-defined mass at the porta hepatis compressing the common bile duct. He underwent endoscopic retrograde cholangiopancreatography with stenting and ultrasound-guided biopsies. Histologic sections showed a neoplastic population of small ovoid cells with a high N:C ratio, nuclear hyperchromasia, "smoky" chromatin and abundant mitotic figures, and characteristic of high-grade neuroendocrine carcinoma (HGNECA). Immunohistochemistry showed synaptophysin, chromogranin, Golgi pattern CK20 reactivity, and strong diffuse expression of Merkel cell polyomavirus, supporting a diagnosis of Merkel cell carcinoma (MCC). A metastatic workup, including complete skin examination and positron emission tomography scan, revealed no other site of disease. Although this patient fits the classic demographic pattern for MCC, he lacks cutaneous involvement and significant risk factors for MCC including immunosuppression and concurrent or previous malignancy. Histologically, the differential diagnosis in this anatomical site is primary or occult metastatic organ-based small-cell HGNECA. Although pure nodal MCC accounts for a minute subset of MCC, it is almost exclusively described in superficial and extremity-draining nodal basins (eg, axillary or inguinal regions). Primary visceral nodal MCC accounts for fewer than 5 cases ever reported. This case illustrates the importance of recognizing the morphologic features characteristic of MCC, regardless of anatomical location, and the value of immunohistochemistry in diagnosis, which aid in differentiating it from non-MCC mimics. Development of targeted therapy has made distinction between MCC and non-MCC HGNECA increasingly important. This patient initially responded to PD-L1 inhibitor therapy but ultimately died with disease 10 months after diagnosis.