INTRODUCTION
Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine skin tumor that typically presents in elderly white males with an extensive history of sun exposure.1 MCC favors the head or neck, but has been described on the extremities and trunk.2 Risk factors include ultraviolet light exposure and fair skin. Extensive UV damage is implicated as the primary driver of malignant transformation in 20% of MCCs. Merkel cell polyomavirus, a common virus estimated to infect 60% to 80% of the general population, is thought to play a driving oncogenic role in 80% of cases.1,3 Although rare, the total incidence in the US is increasing and projected to exceed 2800 cases/year in 2020 with a likely rise to 3250 cases/year in 2025.4 MCC is an aggressive malignancy with a poor prognosis and a high risk of local recurrence and nodal metastasis. Guidelines for diagnosis and prognosis involve skin and lymph node examination, biopsy (suspicious lesion and sentinel lymph node), histological assessment (cytokeratin 20 (CK-20), synaptophysin, CD56), imaging and consultation with a multidisciplinary tumor board.1
MCC typically presents as an erythematous or violaceous nodule. It has also been reported in literature to resemble papules, plaques, cysts, telangiectatic papules, pruritic tumors, pedunculated lesions, and subcutaneous masses.1 According to one study, a majority of MCC cases were originally thought to be benign (56%).5 Given the incidence of atypical presentations, it is important to consider a broad differential when evaluating new growths. Here we report 2 cases of MCC on the extremities that presented as a firm plaque and a cystic nodule, illustrating the deceptive and varied presentation of MCC. We provide a review of MCC case reports and summarize tools that may aid in earlier diagnosis of MCC as well as implications of primary tumor location in prognosis.
MCC typically presents as an erythematous or violaceous nodule. It has also been reported in literature to resemble papules, plaques, cysts, telangiectatic papules, pruritic tumors, pedunculated lesions, and subcutaneous masses.1 According to one study, a majority of MCC cases were originally thought to be benign (56%).5 Given the incidence of atypical presentations, it is important to consider a broad differential when evaluating new growths. Here we report 2 cases of MCC on the extremities that presented as a firm plaque and a cystic nodule, illustrating the deceptive and varied presentation of MCC. We provide a review of MCC case reports and summarize tools that may aid in earlier diagnosis of MCC as well as implications of primary tumor location in prognosis.
CASE REPORTS
Patient 1
An 84-year-old Asian female with no significant past medical history (PMH) presented with an asymptomatic lesion on her left posterior leg. The patient noticed the spot about one month prior to evaluation. She denied any pain, bleeding, or discharge and denied any current or past treatment of the lesion.
On examination, a 1cm- x 1-cm well demarcated, pink, non-tender firm plaque was noted on the left proximal posterior leg (Figure 1). Based on the clinical presentation, differential diagnoses included erythema induratum, erythema nodosum, MCC, and other granulomatous processes.
An 84-year-old Asian female with no significant past medical history (PMH) presented with an asymptomatic lesion on her left posterior leg. The patient noticed the spot about one month prior to evaluation. She denied any pain, bleeding, or discharge and denied any current or past treatment of the lesion.
On examination, a 1cm- x 1-cm well demarcated, pink, non-tender firm plaque was noted on the left proximal posterior leg (Figure 1). Based on the clinical presentation, differential diagnoses included erythema induratum, erythema nodosum, MCC, and other granulomatous processes.
