Merkel cell carcinoma: is this a true carcinoma?

Recent years have brought an enhanced understanding of Merkel cell carcinoma (MCC) biology, especially with regard to the Merkel cell polyoma virus as a causative agent. Differences between Merkel cell polyomavirus‐positive and Merkel cell polyomavirus‐negative MCC in morphology,^, gene expression, miRNA profiles and prognosis have been reported. Origin of MCC is controversial. Presence of neurosecretory granules has suggested that these carcinomas originate from one of the neurocrest derivatives, most probably Merkel cells; the name Merkel cell carcinoma is now widely accepted. Expression of PGP 9.5, chromogranin A and several neuropeptides, initially regarded as specific markers for neural and neuroendocrine cells, has recently been shown in a subset of lymphomas. MCC commonly expresses terminal deoxynucleotidyl transferase and PAX5. Their co‐expression under physiologic circumstances is restricted to pro/pre‐B cells and pre‐B cells. These findings lead to the hypothesis by zur Hausen et al. that MCC originates from early B cells. This review was intended to critically appraise zur Hausen's hypothesis and discuss the possibility that MCC is a heterogenous entity with distinct subtypes.     

Nevoid basal cell carcinoma syndrome or multiple hereditary infundibulocystic basal cell carcinoma syndrome?

We present a case of nevoid basal cell carcinoma syndrome, also known as Gorlin syndrome, or basal cell nevus syndrome, which clinically follows a course more consistent with multiple hereditary infundibulocystic basal cell carcinomas or multiple hereditary trichoepitheliomas. The following article describes the case in detail and gives an overview of other genodermatosis, which were initially considered in the differential and which may be linked pathogenetically.     

CD56 staining in Merkel cell carcinoma and natural killer‐cell lymphoma: magic bullet,diagnostic pitfall,or both?

Background: Antibodies to CD56 label natural killer (NK) cell lymphomas and neuroendocrine tumors such as Merkel cell carcinoma (MCC). In MCC altered by crush artifact or obscured by lymphocytes, the histologic features coupled with CD56 positivity can lead to an erroneous impression of NK‐cell lymphoma. Methods: Eighteen cases of MCC were stained for CD56, CK20, MNF116, and pankeratin. The results were compared to histologic features and CD56 staining pattern of three NK‐cell lymphomas. Results: Three of 18 cases of MCC histologically resembled lymphoma, and CD56 positivity with CD3 and CD20 negativity initially raised the possibility of NK‐cell lymphoma. Two additional cases were obscured by dense inflammation, again suggesting the diagnosis of lymphoma. Seventeen of 18 MCC labeled for CD56 and an equal number stained for CK20. All MCC tested were positive for CAM5.2 (14/14) and MNF116 (17/17). Antibodies to pankeratin labeled only one of 18 MCC. Staining for CD56 was stronger in MCC than NK‐cell lymphomas. Conclusions: CD56 is a sensitive marker for MCC as well as for NK‐cell lymphoma, but is not specific. Importantly, CD56 positivity in crushed or inflamed biopsies of MCC may lead to an erroneous impression of NK lymphoma. Awareness of this potential pitfall will prevent misdiagnosis.     

What's your assessment? Basal cell carcinoma

The "What's Your Assessment?" series includes a short case presentation and differential diagnosis. It is followed by a discussion of the disease or condition and the rationale used in each step of the assessment.     

Merkel细胞和Merkel细胞癌

Merkel细胞癌是起源于Merkel细胞的一种比较少见,具有独特临床症状和组织病理学特点的低度恶性肿瘤,多见于老年.Merkel细胞1975年Merkel首先描写了在某些哺乳动物表皮的基底细胞层内有一种圆形细胞,是一种受有髓神经纤维支配,司触觉的神经末梢器官.以后其他研究者们在人类皮肤的表皮和口腔粘膜上也证明有这些细胞的     

Merkel cell carcinoma metastatic to the transverse colon: Disease free after six years – cure or just prolonged remission?

Merkel cell carcinoma is an uncommon but highly immunogenic skin malignancy that has the potential to metastasize to any site in the body. Despite treatment many patients experience relapse, often to distant sites beyond the site of initial treatment. The development of distant soft tissue or visceral metastases is considered incurable, despite treatment with prognosis usually being measured in months. We report the case of an elderly man who developed colonic metastases from a head and neck primary and with treatment has survived disease free for over 6 years. Such reports are infrequently documented and highlight the unpredictable nature of this disease.     

Merkel cell tumor in a trichilemmal cyst: collision or association?

An 86-year-old white male presented with an erythematous, painless, slowly growing, and firm left thigh nodule. Histologic examination revealed a dermal proliferation of monomorphous cells arranged in trabeculae, nests, and sheets with an infiltrative growth pattern. The cells had a high nuclear-cytoplasmic ratio, finely granular nuclear chromatin, and nuclear molding. Numerous mitotic figures, apoptotic cells, and individual cell necrosis were present; lymphovascular invasion was identified. The tumor was attached, demonstrating pagetoid intraepithelial migration, to a follicular cyst lined by squamous epithelium, lacking a granular cell layer and filled with compact keratinous content, diagnostic of trichilemmal cyst. Immunohistochemical study revealed that tumor cells expressed pan-cytokeratin (CK), chromogranin, synaptophysin, neuron-specific enolase, and CK20 (dotlike staining pattern), thus supporting the diagnosis of Merkel cell carcinoma. The association of Merkel cell carcinoma with a cyst is an exceptionally rare occurrence. As a result of the prominent involvement of the cyst wall by tumor cells, we favor that in this case carcinoma arose in the trichilemmal cyst rather than being a collision tumor. This hypothesis is also supported by the recent observation that Merkel cells are frequently present within normal hair follicles, especially in the isthmic portion that corresponds with the area of origin of the trichilemmal cyst.