Rapidly Progressive Merkel Cell Carcinoma with Atypical Metastatic Pattern—A Case Report and Brief Literature Review

<b>Background and Clinical Significance:</b> Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine cutaneous malignancy with increasing incidence among elderly, immunocompromised patients or individuals exposed to ultraviolet radiation. <b>Case Presentation:</b> We present the case of an 84-year-old Caucasian male with no history of immunosuppression, who was admitted for asthenia, dysphagia, weight loss, and generalized weakness. Clinical and imaging investigations revealed a violaceous tumor on the right arm and disseminated metastases affecting the liver, spleen, bones and lymph nodes. A liver biopsy confirmed a small round blue cell neoplasm suggestive for MCC, although immunohistochemistry could not be performed due to the patient's fulminant deterioration and death within 12 days of admission. <b>Conclusions:</b> This case is notable for its exceptionally rapid progression, particularly splenic involvement, and absence of known immunosuppressive factors. It highlights the existence of highly proliferative MCC subtypes with potential for bypassing classical metastatic pathways. Early clinical suspicion and prompt histological evaluation are essential for diagnosis, although the prognosis remains poor in advanced stages. Due to fulminant deterioration, immunohistochemistry could not be performed; therefore, the diagnosis is highly suggestive based on clinical, imaging, and morphological correlation.