Merkel cell carcinoma: Clinicopathological analysis of three patients and literature review.

To investigate the clinicopathological features of three patients with Merkel cell carcinoma (MCC). The clinicopathological features, immunophenotypes, diagnosis and differential diagnosis, treatment, and prognosis of the three patients with MCC were analyzed retrospectively. Among the three patients, two were male and one was female. The age range of the patients was 55-79 years, while their mean age was 66.6 years. The maximum and mean tumor diameters were 1.8-2.5 cm and 2.1 cm, respectively. The tumors were located in surface areas such as the face and forearm. The tumor masses were mostly round, with a gray, solid appearance and qualitative sections. Microscopic examination revealed that the MCCs of the three patients had roughly the same morphology. Light microscopy indicated that the MCCs appeared as an intradermal mass with a narrow "Grenz band" separated from the epidermis, often accompanied by necrosis (apoptotic bodies) and patchy lymphocyte infiltration. Histological assessment of the MCCs showed monomorphic cell hyperplasia with cables, trabeculae, or sheet formation, hyperchromatic nuclei, vacuoles, cytoplasm with a "salt and pepper" appearance, and nuclear division. Immunophenotyping found tumor cells that were CK (+), CD56 (+), Syn (+), EMA (+), β-catenin (membrane +), LCA (-), CD99 (-), S100 (-), HMB-45 (-), SOX-10 (-), TTF-1 (-), CDX-2 (-), and CD34 (-), along with a Ki-67 proliferation index of 60-70%. Of the three patients with MCC, two were immunophenotypic CgA negative and one was positive. Additionally, two immunophenotypes exhibited CK20 negativity, and one showed paranuclear punctate positivity for CK20. MCC is a highly malignant cutaneous neuroendocrine carcinoma, requiring the combination of pathological morphology examination and immunophenotyping to confirm the diagnosis. Moreover, the primary MCC treatment of surgical treatment should be supplemented with chemotherapy and/or local radiotherapy to alleviate its poor prognosis, easy recurrence or metastasis, and high mortality.