Does Squamous Cell Cancer Turn into Melanoma?

Squamous cell skin cancer can be quite serious in a minority of cases, but it does not “turn into” melanoma. Melanoma is a deadly cancer that arises from melanocytes, a different type of skin cell than squamous cells.

Squamous cell skin cancer (squamous cell carcinoma) is one of the most common types of skin cancer that occurs when cells in the top layer of skin (the epidermis) grow out of control. 

There are 3 main types of cells in the top layer of the skin (epidermis) where cancer can form:

• Squamous cells
  • These are flat cells in the upper (outer) part of the epidermis, that constantly shed as new ones form
  • These cells can develop into squamous cell skin cancer 
  • About 20% of skin cancers are squamous cell carcinomas 
• Basal cells
  • These cells are in the lower part of the epidermis (basal cell layer) and they constantly divide to form new cells to replace the squamous cells that wear off the skin’s surface
  • Skin cancers that originate in this layer are called basal cell skin cancers (basal cell carcinomas)
• Melanocytes
  • These cells produce the brown pigment called melanin that gives the skin its tan or brown color
  • Melanin acts as the body’s natural sunscreen, protecting the deeper layers of the skin from some of the harmful effects of the sun. 
  • Melanoma skin cancer starts in these cells

Squamous cell cancer cannot turn into melanoma since each type of cancer arises from different types of cells in the skin. It is possible, however, to have both squamous cell skin cancer and melanoma skin cancer at the same time.

Squamous cell cancer can occur anywhere on the skin, but it tends to develop on sun-exposed areas of the body such as the face, ear, scalp, shoulders, neck, lips, backs of the hands, and forearms. 

Squamous cell cancers may look like:

• Rough or scaly red patches, which might crust or bleed
• Raised growths or lumps, sometimes with a depressed area in the center
• Open sores (that may ooze or crust over) that don’t completely heal, or that heal and return
• Wart-like growths
• A flat area that is only slightly different from normal skin

Most squamous cell skin cancers are caused by repeated and unprotected skin exposure to ultraviolet (UV) light from sunlight and tanning beds. 

Risk factors for developing squamous cell skin cancer include: 

• Ultraviolet (UV) light exposure (sunlight and tanning beds)
• Having light-colored skin
• Being older
• Being male
• Exposure to certain chemicals
  • Arsenic, coal tar, paraffin, and certain types of petroleum products 
• Radiation treatment 
• Previous skin cancer
• Long-term or severe skin inflammation or injury
  • Scars from severe burns, areas of skin over serious bone infections, and skin damaged by some severe inflammatory skin diseases 
• Psoriasis treatment
  • Psoralens and ultraviolet light (PUVA) treatments 
• Xeroderma pigmentosum (XP)
• Basal cell nevus syndrome (also known as nevoid basal cell carcinoma syndrome or Gorlin syndrome)
• Weakened immune system (such as from certain diseases or medical treatments) 
• Smoking

Squamous cell skin cancer is diagnosed with a physical examination of the skin and patient history, along with tests such as: 

• Skin biopsy
  • Shave (tangential) biopsy
  • Punch biopsy
  • Excisional biopsy: removes the entire tumor
  • Incisional biopsy: removes only a portion of the tumor
• Lymph node biopsy
  • Fine needle aspiration (FNA) biopsy
  • Surgical (excisional) lymph node biopsy
• Imaging tests 
  • Used if it is suspected cancer has spread deeply below the skin or to other parts of the body
  • It is uncommon for squamous cell cancers to spread 
  • Tests may include computerized tomography (CT) scan or magnetic resonance imaging (MRI) scan

Treatment for squamous cell cancer may include one or more of the following:

• Surgery 
  • Excision: removes the entire tumor
  • Curettage and electrodesiccation: cancer is removed by scraping it with a long, thin instrument with a sharp looped edge on one end (a curette) and the area is treated with an electric needle (electrode) to destroy any remaining cancer cells
  • Mohs surgery (also called Mohs micrographic surgery, or MMS): removes one layer of skin at a time, samples are checked for cancer, and the process is repeated until there are no cancer cells in the skin sample. Process can be slow but can leave more tissue intact.
  • Lymph node surgery
    • Biopsy
    • Lymph node dissection: many nodes are removed 
  • Skin grafting and reconstructive surgery
• Local treatments other than surgery 
  • Cryotherapy: liquid nitrogen is applied to the tumor to freeze and kill cancer cells
  • Photodynamic therapy (PDT): a drug is applied to the skin as a gel or liquid that makes the cells sensitive to certain types of light, and a special light source is then focused on the tumor(s), to kill the cells
  • Topical chemotherapy: anti-cancer medicine is put directly on the skin, usually as a cream or ointment
    • 5-fluorouracil (5-FU) (Efudex, Carac, and Fluoroplex)
  • Immune response modifiers
    • Interferon 
  • Laser surgery: uses a beam of laser light to vaporize cancer cells
• Radiation therapy
  • Used when a tumor is very large or is on an area of the skin that makes it hard to remove with surgery
  • Also useful for some patients who can’t have surgery
  • Can often cure small squamous cell skin cancers and can delay the growth of more advanced cancers
• Systemic chemotherapy 
  • Cisplatin 
  • 5-fluorouracil (5-FU) 
• Targeted therapy 
  • Hedgehog pathway inhibitors: vismodegib (Erivedge) and sonidegib (Odomzo)
  • EGFR inhibitors: cetuximab (Erbitux)
• Immunotherapy for advanced squamous cell skin cancers
  • Immune checkpoint inhibitors called PD-1 inhibitors: cemiplimab (Libtayo) and pembrolizumab (Keytruda) 

Squamous cell skin cancers may be prevented in some cases. 

• Limit exposure to ultraviolet (UV) rays
  • Stay in the shade
  • Wear sunscreen
  • Wear a shirt and hat
  • Wear sunglasses to protect eyes
  • Avoid tanning beds and sun lamps
• Check your skin regularly for any abnormal areas, new growths, or skin changes, and see a doctor if you notice any changes
• Avoid harmful chemicals, such as arsenic, which may be found in well water in some areas, pesticides and herbicides, some medicines and imported traditional herbal remedies, and in certain occupations (such as mining and smelting)
• Don’t smoke
• Avoid risk factors that weaken the immune system 
  • Avoid intravenous (IV) drug use 
  • Don’t have unprotected sex with many partners
• Take medications that can lower the risk of developing squamous cell skin cancer
  • For people at increased risk of developing skin cancer, such as people with certain inherited conditions or a weakened immune system, there are medicines that could lower the risk (chemoprevention)