4 Types Of Skin Cancer And How They’re Diagnosed

Skin cancer is one of the most common types of cancer in the U.S. Approximately one in five Americans¹ will develop some form of skin cancer in their lifetime.

All forms of cancer are highly complex and can be caused by various factors—and skin cancer is no different.

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What is skin cancer?

Within our bodies, our cells are constantly replicating and growing. The death and subsequent regeneration of cells cause rapid and constant turnover, and it’s how we heal and repair our bodies. Cancer will occur when cells divide and grow in an uncontrolled manner. This abnormal pattern of growth causes dysregulation and results in a spread to neighboring tissues.

Cancer keeps growing as the cells multiply over and over. When cancer cells grow through normal body tissue, this can create a tumor. This can then spread to other areas of the body, resulting in metastasis or a secondary tumor. While most cancers are due to gene changes that occur over a patient’s lifetime, some cancers can be genetic and due to the inheritance of faulty genes down family lines.

Skin cancer is classified as the uncontrollable growth of abnormal cells in the outermost skin layer, called the epidermis. When DNA damage goes unrepaired, this triggers the development of mutations, which cause skin cells to multiply rapidly and form tumors.

There are four main types of skin cancer: squamous cell carcinoma, melanoma, basal cell carcinoma, and Merkel cell cancer. While there are a few other skin cancer types, like sarcomas, they are all classified as non-melanoma skin cancers and are rare. 

You might also be wondering what skin cancer is most common. Here’s a rundown of the different types of skin cancer.

1. Squamous cell carcinoma

Squamous cell carcinoma, or SCC, is a common form of skin cancer. It’s characterized by abnormal, accelerated growth of squamous cells. 

SCC can occur when DNA damage from exposure to ultraviolet (UV) radiation or other damaging agents triggers abnormal squamous cells. It’s a relatively slow-growing type of skin cancer, and when caught early, most SCCs are curable. 

These carcinomas are most commonly found on exposed areas of the body damaged by UV rays, like the chest, arms, neck, and hands. 

What is a squamous cell?

Squamous cells are one of three main types of cells in the top layer of the skin (the epidermis). Squamous cells are thin, flat cells located near the skin’s surface that shed continuously as new ones form. They are also commonly found in the tissues that form the surface of the skin, linings of hollow body organs, and the lining of the respiratory and digestive tracts.

The prevalence and danger of squamous cell carcinoma

While most squamous cell carcinomas (SCC) can be successfully treated, if they’re allowed to grow, these lesions can become dangerous and deadly. When left untreated, SCCs can become invasive, grow into deeper layers of skin, and spread to other body parts. 

SCCs can also be disfiguring, as they can appear as rough and red patches, open sores, thickened or wart-like skin, or raised growths. Also, SCCs may crust over, itch, or bleed.

Generally, SCC is less common than basal cell carcinoma (BCC). However, the number of reported SCC cases in the U.S. is steadily increasing. Approximately 1.8 million cases² of SCC are diagnosed each year, and SCC incidence has increased around 200% in the past thirty years.

2. Melanoma

Melanoma is one of the most well-known and common types of skin cancer and develops when melanocytes grow rapidly and out of control. Melanocytes are cells that give the skin a brown color, or a tan.

Melanoma is less common than basal cell carcinoma and squamous cell carcinoma. However, it’s more dangerous, as it can spread to other organs more rapidly if not treated early.

What is a melanocyte?

Melanocytes are a type of skin cell that produces a pigment called melanin, which gives skin its color. Melanocytes are also found in the upper layer of the skin. 

Researchers found that two types³ of melanin exist, called eumelanin and pheomelanin. People who are naturally darker-skinned have more eumelanin, and naturally fair-skinned people have more pheomelanin.

Eumelanin can help protect the skin from sun damage. However, this effect is not observed in pheomelanin. Because of this, people with dark skin are at a much lower risk⁴ of developing melanoma in comparison to fairer-skinned individuals. Fair-skinned people have less eumelanin and are therefore more susceptible to burning, skin damage, and the subsequent development of skin cancer.

Skin can be exposed to UV radiation from the sun or tanning beds. When this occurs, it causes skin damage that can trigger melanocytes to produce more melanin. Only the eumelanin pigments attempt to protect skin by causing tanning to occur.

When DNA damage from skin burning or tanning from UV radiation triggers changes and mutations in the melanocytes, this can lead to uncontrolled cell growth and the development of melanoma.

How dangerous is melanoma?

When detected and treated early, melanoma is generally curable for most of the population. Researchers estimate that the five-year survival rate for U.S. patients with melanoma that is detected early is about 99%⁵. However, once melanoma has spread to other parts of the body or deeper into the skin, this makes it more difficult for doctors to treat, and this can quickly become deadly.

The four types of melanoma

Melanoma is a complex type of skin cancer and it affects various sites on the body. While there are many different types of melanoma, here are four of the more common ones.

1. Superficial spreading melanoma

Superficial spreading melanoma is the most common form of melanoma and can either arise in an existing mole or appear as a separate lesion. When it occurs in a mole already in the skin, this type of melanoma often grows on the skin’s surface for some time before penetrating deeper.

Superficial spreading melanoma can be found nearly everywhere on the body of both sexes, but it’s commonly seen on the torso of men, on the legs of women, and on the upper back of both.

2. Lentigo maligna

Lentigo maligna often develops in older people, and when skin cancer spreads beyond the original site or becomes invasive, it’s known as lentigo maligna melanoma. 

This form of melanoma is similar to superficial spreading melanoma, as it usually grows on the skin surface in the initial stages. This tumor generally appears on sun-damaged or sunburnt skin on the face, ears, arms, and upper torso.

3. Acral lentiginous melanoma

In people of color, especially those of African descent, this is the most common form of melanoma⁶. It may appear as a brown or black area and grows in harder-to-spot areas, like under the nails and on the feet and hands.

4. Nodular melanoma

Nodular melanoma⁷ is one of the most aggressive types of melanoma, and it accounts for 10–15% of all melanoma cases. Unlike other types, this tumor rapidly grows deeper into the skin and can be frequently found on older men’s arms, legs, torso, and scalp. By the time it’s first diagnosed, it is usually already invasive.

3. Basal cell carcinoma

Basal cell carcinoma arises from the uncontrollable growth of basal cells. It’s the most prevalent form of skin cancer, affecting approximately 3.6 million U.S. patients every year. Generally, this form of skin cancer grows and spreads relatively slowly, so it’s mostly curable when caught in the early stages.

Basal cell carcinoma often occurs when there’s DNA damage from exposure to UV radiation. When this happens, this can trigger changes in basal cells in the epidermis resulting in abnormal cell growth.

What is a basal cell?

Basal cells are one of the main types of cells in the top layer of the skin. These cells are in the lower part of the epidermis, which is called the basal cell layer. They constantly divide and replicate to form new cells that replace squamous cells once they wear off the skin’s surface. While moving up the epidermis, basal cells gradually become flatter until they eventually become squamous cells.

The prevalence of basal cell carcinoma

Basal cell carcinoma is quite a common skin cancer type, and the number of reported cases in the U.S. only continues to increase. Approximately 3.6 million⁸ U.S. patients are diagnosed with BCC each year.

Skin cancer is already incredibly prevalent, with more than one out of every three new cancers being skin cancers; however, the vast majority are BCCs.

4. Merkel cell cancer

Merkel cell carcinoma is incredibly rare, and it’s classified as an aggressive form⁹ of skin cancer that often returns and spreads within two or three years after the initial diagnosis. It’s so rare that only one in 130,000 people in the U.S. will be diagnosed with Merker cell carcinoma.

It’s often due to various risk factors, but most commonly from exposure to the sun, fair skin, being over 50 years of age, and a weakened immune system.

What is a Merkel cell?

These types of cells are located deep in the top layer of the skin and right below the epidermis. What makes Merkel cells unique is that they are connected to nerves, signaling touch sensations, and are very close to specific nerve endings.

How dangerous is Merkel cell carcinoma?

Merkel cell carcinoma (MCC) tumors can often appear on sun-exposed areas of the body. They rapidly proliferate, and MCC is about twice more likely¹⁰ to be deadly compared to melanoma. 

However, with early detection, doctors can successfully treat MCC in patients. If you think you might have MCC, see your doctor. Once the disease has spread, treatment becomes increasingly complex. However, new options are constantly available as research improves.

How skin cancer is diagnosed

The process of diagnosing skin cancer usually starts with a visual examination by a doctor. The American Cancer Society recommends self-examinations on a monthly basis and doctor visits once a year to screen for potential skin cancer. 

When a suspicious-looking spot is found, your doctor will examine the area and note down the shape, size, color, and texture. They will also note if it’s bleeding or scaly. It’s also common for your doctor to look at your nearby lymph nodes to see whether they are enlarged.

If a primary care physician is seeing you, they may refer you to a specialized dermatologist who can order more tests and make a conclusive skin cancer diagnosis.

A dermatologist commonly uses special microscopes or a magnifying lens to examine the suspicious spot (called dermatoscopy) closely. In most cases, the skin cancer can be removed in the dermatologist’s office. But if a dermatologist determines the skin cancer is melanoma or Merkel cell carcinoma, more aggressive treatment may be required.

What are the different stages of skin cancer?

Skin cancer occurs in different stages. The American Joint Committee on Cancer¹¹ was successful in developing a system for describing the stages of skin cancer in patients. Using this system allows doctors to determine how advanced skin cancer is and the next course of action. 

The system is composed of three key pieces of information:

  • T (tumor): The doctor will analyze the tumor’s size, location, and how deep it has grown into the skin.

  • N (node): In this stage, some cancer cells may have spread to nearby lymph nodes or lymph node channels.

  • M (metastasis): This stage refers to whether the skin cancer cells have spread to distant organs. This is also known as stage III melanoma.

The lowdown

There are various types of skin cancer, and depending on which type is observed, this will affect the development and diagnosis of the skin cancer.

While all of these skin cancer types are dangerous if left untreated, some are more prevalent than others. They also all vary in their specific color, size, shape, and location on the body.

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