Skin anatomy and types of skin cancer

Skin Anatomy

The skin is the largest organ of the body and made up of three main layers:

• The Epidermis – very thin upper layer, temperature changes and infections.
• The Dermis – much thicker middle layer that contains hair follicles and nerves as well as many blood and lymph vessels embedded in a collagen-rich framework.
• The Subcutis – deepest fat and collagen rich insulating layer that also contains abundant blood and lymph vessels. 

Most skin cancers develop from cells found in the epidermis layer of the skin. Keratinocytes are the main cells in this layer. Deep in the epidermis, closest to the dermis, these cells are plump and are actively generating new skin cells. This is the layer of basal cells. As these cells age they move upwards towards the surface and thin, becoming the squamous cells. In amongst the basal cells are brown tan pigment (melanin) making melanocyte cells. Close by are other cells (Langerhans cells) that pick up and carry foreign material (eg bacteria or cancer cells) from the skin to the lymph nodes via the lymph vessels. 

Lymph vessels from the skin drain into the local lymph nodes of the groin, armpits and neck. These vessels carry lymph fluid, representing one of the methods of fluid circulation in the body and a route for the immune system. It is also the route that skin cancer cells can use to spread around the body. The lymph nodes act as filters and catch these cells. They can then multiply in the node making it big enough for doctors to feel through the skin.

Types of Skin Cancer

Skin cancers are divided into two main groups – non melanoma skin cancers (NMSC) and melanoma.

Non-melanoma skin cancer
• BCC (basal cell carcinoma) – this is the commonest (80%) skin cancer, sometimes called a ‘rodent ulcer’. They tend to be slow growing, just causing a local problem. It is extremely uncommon for them to spread to other parts of the body (metastasis).
• SCC (squamous cell carcinoma) – this is the second most common skin cancer type. They can often appear warty and crusted. These can metastasise elsewhere and must be treated early.
• Other rare skin cancers – there are 22 recognised rare skin cancer types which combined make up about 500 cases a year (compared with over 13,000 melanoma cases per year and 130,000 NMSC cases per year). 

Melanoma is less common than basal cell carcinoma or squamous cell carcinoma but can be far more serious. More than 95% are shades of brown (melanin skin pigment) and develop in previously ‘normal’ moles that change (30%) or begin as completely new moles (70%). Catching these early is vital. 

If you have a growth on the skin that regularly forms a crust or bleeds and does not heal over a 6–8 week period, you should have it checked by your doctor

Read More

Basal cell carcinoma
Squamous cell carcinoma
Malignant melanoma
Surgery and reconstruction
Lymph node surgery
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