What is skin cancer?
Skin cancer is a condition where the cells in the skin mutate to an abnormal type and divide uncontrollably. Skin cancer is the most common cancer in the fair-skinned populations in many regions of the world. Men and women are affected equally [1, 2].
The most common types of skin cancers are non-melanoma cancers, including basal cell carcinoma and squamous cell carcinoma, representing approximately 30% of new skin cancers diagnosed every year [3]. Melanomas, on the other hand, are less common but can be more dangerous due to the potential to metastasise and spread to other parts of the body [1].
The primary cause or skin cancer is exposure to sunlight, which contains UV radiation. This causes DNA mutations in the skin cells, transforming them into cancerous cells. Interestingly, UV damage induces a well-defined set of genetic changes, which is referred to as mutational signature, which can be used to support the diagnostic process [1, 2]. Besides UV radiation, skin cancer can be caused by exposure to chemicals, certain viruses, as well as a genetic predisposition [4].
As early detection of suspicious skin changes improves the patient's prognosis, it is important to routinely visit the dermatologist to examine moles and skin changes. Thanks to improvements in diagnostics and treatment, the patient prognosis is improving [1].
What is merkel cell carcinoma and how is it diagnosed and treated?
Merkel cell carcinoma (MCC) is a rare, but very aggressive type of skin cancer, which is typically found in older patients. It presents as a red or bluish node on the skin (cutaneous) or under the skin (subcutaneous), most usually located on the extremities or the head and neck region [5, 6]. As with every cancer, MCC is a heterogeneous disease, and there are multiple presentations and risk factors. It is often associated with immunosuppression (decreased functionality of the immune system), chronic UV light exposure, and infection with the Merkel cell polyomavirus, a type of virus that infects and integrates into the DNA of neuroendocrine cells of the skin (cells that excrete neurotransmitters and regulate hormones) [7].
MCC originates from a malignant transformation of Merkel cells. Merkel cells are cells in the epidermis, the outermost layer of the skin. They have roles associated with the nervous system and the endocrine system, particularly with detection of light tactile stimuli and transmitting the information through the nervous system. Additionally, the cells secrete peptides to facilitate signalling in the skin to maintain its homeostasis (the function to maintain a stable environment).
The diagnosis of MCC is challenging at first, as it can be mistaken for other skin conditions due to its appearance. MCC often resembles cherry angioma, a benign (non-cancerous) lesion of the skin. The diagnosis is made by biopsy (taking a small sample) or excision (removing the node completely) of the suspected node, and its histological evaluation and immunohistochemical tests. These involve slicing the node in very thin slices and staining with specialised dyes that bind to certain cell types and/or molecules, so that they are visible under the microscope. Common histological findings include the presence of uniform round cells expressing cytokeratin 20, neurofilament, synaptophysin, chromogranin, and neuron-specific enolase [8].
As MCC is very aggressive, its prognosis is generally poor, with a 5 year survival between 30% to 74% [8, 9]. This cancer is twice as lethal as melanoma, with more than a third of patients eventually dying from this cancer [10].
The first-line treatment for MCC is the removal of the primary tumour (the skin lesion) with wide safety margins to ensure that all cancer cells are removed. Radiotherapy to the primary side is recommended to ensure that all cancerous cells are killed [11, 7]. Biopsy of adjacent lymph nodes is also recommended, as invasion of lymph nodes is a sign of worse prognosis, and required further therapeutic action such as irradiation of the lymph nodes. This is also recommended prophylactically, as radiotherapy to the adjacent lymph nodes can reduce the rate of regional recurrence (the cancer coming back in the same place) [7]. For advanced MCC, checkpoint inhibitors (a type of immunotherapy that targets certain molecules in the cell that facilitate progression along the cell cycle) targeted against the PD-1/PD-L1 axis have proven to be highly effective with a lasting response [7]. In cases of distant metastasis, systemic chemotherapy is indicated [12].
What is cherry angioma and is it cancer?
Cherry angioma, also known as Campbell de Morgan spots, is a relatively common, benign skin growth, most prevalent in the older population. The growth is intertwined with small blood vessels, giving it a red to purplish appearance. They are typically harmless, unless they change appearance or start to bleed, which may be a sign of skin cancer [13].
As cherry angiomas are benign, they do not require treatment for medical reasons and patients opt for treatment for cosmetic reasons. A variety of therapeutic approaches exist to remove cherry angiomas, including laser therapy and nonlaser therapy [14, 13]. Nonlaser therapies include cryotherapy (freezing the lesion with liquid nitrogen), sclerotherapy (injection of a solution that destroys small vessels), electrosurgery (burning the lesion with an electrocautery tool), and radiofrequency ablation. The choice of treatment depends on the individual's preference and the specific characteristics of the angioma [14, 13]. A discussion with a healthcare professional should result in determining the best treatment approach. All treatments are safe, although some times localised pigmentary changes can occur [13].
Merkel cell carcinoma (MCC) and cherry angiomas are both skin conditions, but they have significant differences in their nature, appearance, and potential health impacts.
What are the main differences?
With a naked eye, it is difficult to distinguish MCC from cherry angioma due to their similar presentation. The only detetminant is observing growth in lesions that can be MCC. It is very important to protect yourself from sunlight, get all spots and moles checked up regularly following the advice given by your doctor.
The colour of the MCC is difficult to distinguish from cherry angioma with the naked eye. Though the lesions look similar, computerised image analysis methods revealed differences between the two lesions, which can be potentially used as a diagnostic tool. A study titled "Color Analysis of Merkel Cell Carcinoma: A Comparative Study with Cherry Angiomas, Hemangiomas, Basal Cell Carcinomas, and Squamous Cell Carcinomas" found significant differences in color parameters between MCC and cherry angiomas [15]. The study used the RGB (red, green, and blue) and the CIE Lab color system to analyze clinical images of the color of the lesion and adjacent normal skin from patients with MCC and cherry angiomas. Significant differences were observed especially in the blue spectrum between MCC and cherry angiomas [15].
