Merkel cell carcinoma is a rare but highly aggressive form of skin cancer that arises from neuroendocrine cells in the skin. These cells, known as Merkel cells, are involved in touch sensation and are located in the basal layer of the epidermis. Unlike more common skin cancers such as basal cell carcinoma or squamous cell carcinoma, Merkel cell carcinoma has a strong tendency to grow rapidly and to spread early to lymph nodes and distant organs.
Although it accounts for a small proportion of all skin cancers, Merkel cell carcinoma carries a disproportionately high risk of recurrence and mortality. The disease primarily affects older adults and is more frequently diagnosed in individuals with fair skin. Because of its rarity and nonspecific early appearance, Merkel cell carcinoma is often misdiagnosed in its initial stages, which can delay appropriate treatment.
Why Is Merkel Cell Carcinoma Considered Aggressive?
Merkel cell carcinoma is considered aggressive because of its biological behavior. The tumor grows quickly, invades surrounding tissues, and has a strong propensity for early metastasis. Studies have shown that a significant proportion of patients already have microscopic spread to regional lymph nodes at the time of diagnosis, even when the primary tumor appears small.
The aggressive nature of this cancer is linked to its neuroendocrine origin. Neuroendocrine tumors tend to have high mitotic activity, meaning that cancer cells divide rapidly. In addition, Merkel cell carcinoma often evades immune surveillance, allowing it to progress without early detection. This combination of rapid growth and immune escape contributes to its poor prognosis if not treated promptly.
What Causes Merkel Cell Carcinoma?
The development of Merkel cell carcinoma is strongly associated with two major factors: ultraviolet (UV) radiation exposure and Merkel cell polyomavirus infection. Chronic UV exposure damages DNA in skin cells, leading to mutations that can drive malignant transformation. This explains why tumors often appear on sun-exposed areas such as the head, neck, and upper limbs.
Merkel cell polyomavirus is detected in a large proportion of Merkel cell carcinoma tumors. In virus-positive cases, the virus integrates into the host genome and produces viral proteins that interfere with normal cell cycle control. In virus-negative cases, UV-induced genetic damage appears to be the dominant mechanism. Importantly, both pathways ultimately lead to uncontrolled cell growth.
How Does Merkel Cell Carcinoma Typically Present?
Clinically, Merkel cell carcinoma often presents as a firm, painless, rapidly growing skin nodule. The lesion is usually red, pink, or violaceous and may have a smooth, shiny surface. Because the tumor is often asymptomatic and does not initially ulcerate, patients may not seek medical attention promptly.
A helpful clinical concept used by clinicians is the “AEIOU” pattern: asymptomatic, expanding rapidly, immune suppression, older age, and ultraviolet-exposed skin. While not diagnostic, this pattern highlights common features seen in many cases. Despite these clues, the tumor can resemble benign lesions or other skin cancers, contributing to delayed diagnosis.
Can A dermatoscope Detect Merkel Cell Carcinoma?
Dermatoscope is a non-invasive tool that allows clinicians to visualize subsurface skin structures, including vascular patterns and lesion architecture, that are not visible to the naked eye. For instance, the IBOOLO DE-4100 PRO dermatoscope features four lighting modes and 10X magnification, providing the user with an exceptionally clear field of view for observation.
Merkel cell carcinoma does not have a single, pathognomonic dermatoscopic pattern. However, studies and clinical observations have identified several features that may raise suspicion. These include a predominantly structureless area, often pink, red, or violaceous in color, along with irregular or polymorphous blood vessels, such as linear, serpentine, or dotted vessels. Shiny white areas corresponding to fibrosis or dermal alteration may also be seen. These findings reflect the tumor’s rapid growth and rich vascular supply but are not specific to MCC.
How Is Merkel Cell Carcinoma Diagnosed?
Diagnosis of Merkel cell carcinoma relies on histopathological examination. A skin biopsy is essential to confirm the diagnosis. Under the microscope, the tumor shows small, round blue cells with high mitotic activity. Because these features overlap with other malignancies, immunohistochemical staining is required.
Specific markers, such as cytokeratin 20 with a characteristic perinuclear dot-like pattern, help distinguish Merkel cell carcinoma from other small cell tumors. Additional imaging studies, including ultrasound, CT, or PET scans, are often performed after diagnosis to assess lymph node involvement and distant metastasis.
How Is Merkel Cell Carcinoma Treated?
Treatment typically involves a multidisciplinary approach. Surgical excision of the primary tumor with clear margins is the cornerstone of management. Because of the high risk of local recurrence, adjuvant radiotherapy is often recommended, even after complete surgical removal.
In recent years, immunotherapy has transformed the treatment landscape for advanced Merkel cell carcinoma. Immune checkpoint inhibitors that enhance the body’s anti-tumor immune response have demonstrated significant and durable responses in many patients. Chemotherapy, once the main systemic treatment, is now used less frequently due to its limited long-term effectiveness.