Cytological and Immunocytochemical Features of Merkel Cell Carcinoma on Fine Needle Cytology Samples: A Study of 22 Cases

The diagnostic utility of Merkel cell polyoma virus immunohistochemistry in cytology specimens

OBJECTIVE

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine neoplasm that predominantly affects elderly and immunocompromised patients. Merkel cell polyoma virus (MCPyV) is clonally integrated into the majority of MCCs and has been linked to patient outcomes, playing a central role in the pathogenesis of the disease. We aimed to assess the utility of MCPyV immunohistochemistry (IHC) in the diagnosis of MCC in cytology cell block specimens and correlating with clinicopathologic features.

METHODS

Fifty-three cytology samples of MCC with sufficient cell block material were stained for MCPyV by IHC and scored semi-quantitatively in extent and intensity. Morphologic mimics of MCC including small cell lung carcinoma (n = 10), non-Hodgkin lymphoma (n = 10), basaloid squamous cell carcinoma (n = 6) and other neuroendocrine carcinomas (n = 8) were stained in parallel. Positive staining was defined as >1% of the tumour cells showing at least moderate staining intensity.

RESULTS

The cytologic features of MCC were characterized by high nuclear-cytoplasmic ratios, hyperchromatic nuclei with 'salt and pepper' chromatin, and nuclear moulding. MCPyV was detected in 24 of 53 cases (45%). Staining was strong and diffuse in roughly half of the positive samples. Of the morphologic mimics, one follicular lymphoma showed strong and diffuse staining. In contrast to prior studies, we saw no association between MCPyV status and patient outcomes.

CONCLUSION

Merkel cell polyoma virus IHC is highly specific (97%) for the diagnosis of MCC in our cohort, and can serve as a useful diagnostic tool for distinguishing MCC for morphologic mimics.

Cytology coupled with immunocytochemistry nails Merkel cell carcinoma: a rare intruder in the cerebrospinal fluid

Merkel cell carcinoma is an uncommon aggressive skin tumor which is well known for its recurrence and metastasis. Leptomeningeal metastasis involving the cerebrospinal fluid is extremely rare. The diagnosis may easily be missed as it simulates other much common small round blue cell tumors. A history of primary diagnosis may not always be available. Awareness and cytomorphological vigilance with judicious employment of appropriate immunomarkers on limited cerebrospinal fluid samples is indispensable for nailing the diagnosis. The tumor cells are usually monotonous small round cells, singly scattered or as loosely cohesive clusters. Cells have round to elongated nuclei with coarsely granular chromatin, nuclear molding at places and scanty basophilic cytoplasm. A limited immunocytochemistry panel employing CK20 and CD56 for which the tumor is positive is confirmatory. We herein present a case of infiltration of cerebrospinal fluid by Merkel cell carcinoma.

EUS-FNA of the Merkel cell carcinoma metastasis to the pancreas: Cytomorphology and immunocytochemistry on direct cytological smears

OBJECTIVE

To report two cases of Merkel cell carcinoma (MCC) metastatic to the pancreas diagnosed with endoscopic ultrasound-guided-fine needle aspiration (EUS-FNA) and to add the case of concomitant chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) and MCC to the literature. The aim is to alert the cytopathologists once more to the problems of differential diagnosis of pancreatic metastasis of MCC and to describe the possibilities of ancillary methods performed on direct cytological smears.

METHODS

EUS-FNA procedures were performed according to standard institution protocol, using 22-G needles with cytopathologist on-site. Based on rapid on-site evaluation (ROSE), additional passes were made for immunocytochemistry (ICC). A mini panel of antibodies was used to aid the differential diagnosis.

RESULTS

Smears revealed a dispersed pattern of small round cells with scant cytoplasm, round nuclei with inconspicuous nucleoli and occasional nuclear moulding, suspicious of small cell carcinoma. Results of ICC applied to the direct cytological smears were as follows: LCA negative, Cytokeratin (clone MNF116) positive, TTF-1 negative, CD 56 positive, NSE weakly positive, Chromogranin A weakly positive and CK20 positive, in one case in a dot-like perinuclear pattern. The diagnosis of MCC was made.

CONCLUSION

Increasing incidence of MCC warrants the inclusion of MCC in the differential diagnosis of tumours of small round blue cell morphology even in unusual sites. The cytomorphological features coupled with an ICC panel are usually enough to make a confident diagnosis of MCC. EUS-FNA is a minimally invasive technique which enables sampling adequate tissue for all the ancillary methods eventually needed to support the diagnosis.

Rapidly growing gastric metastasis of Merkel cell carcinoma, an unusual cause of melena

Merkel cell carcinoma (MCC) is an uncommon, highly aggressive neuroendocrine skin carcinoma that has a tendency for local recurrence and metastatic disease. We report a rare case of recurrent melena in a 77-year-old Caucasian male. Three years earlier, the patient had undergone a radical resection of a para-umbilical MCC. A repeat esophagogastroduodenoscopy proved necessary to identify rapidly proliferating gastric metastasis of MCC as the cause of bleeding.

Immunotherapy with imiquimod and interferon alfa for metastasized Merkel cell carcinoma

Merkel cell carcinoma (mcc) is a highly aggressive neuroendocrine tumour of the skin. Remission rates are high with chemotherapy in patients with metastasis, but without any improvement in overall survival. We present the case of a 90-year-old woman with facial mcc. After radiation and surgery, the mcc recurred with widespread cutaneous and regional lymph node metastases. The metastases were treated with weekly intralesional injections of 1-2×10(6) IU interferon alfa-2a, accompanied by topical imiquimod 5% cream 3 times weekly. After partial regression, subcutaneous pegylated interferon alfa-2b was added at a dose of 30 μg weekly, which was then increased to 50 μg weekly. At 4 months after the start of immunotherapy, all cutaneous metastases and the intralesionally treated lymph node metastases receded. Interruption or reduction of systemic interferon application resulted in locoregional relapses that were successfully treated with surgery or intralesional interferon injections. The patient remains alive 30 months after initiation of immunotherapy, suggesting that locally metastasized mcc might be able to be controlled with local and systemic immunotherapy.