What Is Melanoma?

Melanoma is a type of cancer that originates in melanocytes, the cells responsible for producing melanin, the pigment that gives skin its color. While melanoma can occur in various parts of the body, it is most commonly found on the skin. When melanoma develops on the skin, it is referred to as cutaneous melanoma.

Cutaneous melanoma can appear anywhere on the skin’s surface. However, its location varies depending on skin tone. In individuals with lighter skin, melanoma is more prevalent on the trunk (chest and back) in men and on the legs in women. The neck and face are also frequently affected areas. Conversely, people with darker skin pigmentation have a reduced risk of melanoma in these common locations.

Types of Melanoma Skin Cancer

Melanoma skin cancer is not a single entity but encompasses several distinct types, each with unique characteristics and growth patterns. Understanding these different types is crucial for early detection and appropriate management. The most prevalent types of melanoma include:

Superficial Spreading Melanoma: As the most common form, superficial spreading melanoma accounts for approximately 70% of all cutaneous melanomas. Characteristically, these tumors exhibit a tendency to grow horizontally across the skin’s surface initially. This outward growth pattern often makes them noticeable as a changing dark spot on the skin that may enlarge or alter in shape over time. While some superficial spreading melanomas arise from pre-existing moles, many develop independently.
Nodular Melanoma: Representing about 20% of skin melanomas, nodular melanoma distinguishes itself by its vertical growth pattern. These tumors typically manifest as a raised bump, or nodule, on the skin. Often dark brown or black, they can also present in pink or red hues, potentially complicating early detection. Nodular melanomas are known for their aggressive nature, tending to invade deeper skin layers relatively quickly, which can lead to a more advanced stage at diagnosis compared to superficial spreading melanoma.
Lentigo Maligna Melanoma: Predominantly affecting older individuals, lentigo maligna melanoma typically develops in areas of skin with chronic sun exposure, such as the face, ears, and arms. Initially, it often appears as an irregularly shaped tan or brown flat spot, resembling a large freckle. Lentigo maligna melanoma is characterized by its slow evolution, potentially undergoing changes in size, shape, or color over many years before becoming invasive.
Acral Lentiginous Melanoma (Acral Melanoma): This subtype of melanoma is unique in that it arises on areas of the body with minimal sun exposure, such as the palms of the hands, soles of the feet, and nail beds. Acral melanoma constitutes a significant proportion of melanoma cases in individuals with darker skin tones. It may appear as a dark spot or streak in these less common locations, often diagnosed at a later stage due to its unusual presentation and location.

Melanomas in Other Parts of the Body

While cutaneous melanoma is the most well-known form, melanoma can also develop in areas beyond the skin. These less common locations include:

Ocular Melanoma (Uveal Melanoma): Melanoma can occur inside the eye, specifically referred to as ocular melanoma. The majority of these intraocular melanomas originate in the uvea, the middle layer of the eyeball, and are more precisely termed uveal melanomas.
Mucosal Melanoma: In rare instances, melanoma can arise in the mucous membranes lining various body cavities, such as the nasal passages, oral cavity, throat, and the genital or anal regions. These are known as mucosal melanomas.

Melanomas in these non-cutaneous sites are considerably less frequent than melanoma of the skin.

Distinguishing Melanoma from Other Skin Cancers

It is important to differentiate melanoma from other types of skin cancer. Skin cancers that are not melanoma are broadly categorized as non-melanoma skin cancers. These cancers originate from different skin cells than melanocytes and exhibit distinct behaviors and treatment approaches compared to melanoma.

Basal Cell and Squamous Cell Skin Cancers

Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the most prevalent forms of skin cancer, collectively surpassing all other cancer types in incidence in many regions. Notably, BCCs and SCCs are significantly less likely to spread to distant parts of the body (metastasize) than melanomas. Consequently, they are generally considered less concerning and are managed with different treatment strategies. Detailed information about these cancers can be found in resources dedicated to basal and squamous cell skin cancers.

Less Common Skin Cancers

Beyond BCC and SCC, several other rarer types of non-melanoma skin cancer exist, each requiring specific treatment considerations. These less common types, in aggregate, account for less than 1% of all skin cancer diagnoses.

Benign Skin Tumors

In addition to cancerous growths, various benign (non-cancerous) tumors can develop from different skin cell types.

Benign Tumors Originating from Melanocytes

A mole, also known as a nevus, is a benign skin tumor derived from melanocytes. Moles are extremely common, with nearly everyone having some. While the vast majority of moles are harmless, certain types or a high number of moles can elevate an individual’s risk of developing melanoma. Further information regarding moles and melanoma risk can be found in resources detailing risk factors for melanoma skin cancer.

A Spitz nevus is a specific type of mole that can sometimes mimic the appearance of melanoma, creating diagnostic challenges. Although more frequently observed in children and teenagers, Spitz nevi can also occur in adults. Typically benign and non-spreading, differentiating Spitz nevi from true melanomas can be difficult even under microscopic examination. As a precautionary measure, Spitz nevi are often surgically removed to ensure accurate diagnosis and prevent potential misdiagnosis of melanoma.

Benign Tumors from Other Skin Cells

Various other benign skin tumors arise from skin cells other than melanocytes, including:

Seborrheic Keratoses: These benign growths present as raised spots on the skin with a tan, brown, or black coloration, characterized by a waxy texture and a “stuck-on” appearance.
Hemangiomas: Benign proliferations of blood vessels, hemangiomas are commonly known as “strawberry spots,” particularly when they appear in infancy.
Lipomas: Soft, pliable growths located beneath the skin, lipomas are composed of fat cells.
Warts: Warts are rough-surfaced skin growths caused by specific types of human papillomavirus (HPV).

The majority of these benign tumors have a very low or negligible likelihood of transforming into cancer. Numerous other types of benign skin tumors exist, although most are relatively uncommon.