In order to understand your skin cancer pathology report, you need to know a little more about human skin. Your skin is quite complex. It replaces itself entirely every 4-6 weeks and consists of several layers.
The thin, uppermost layer is called the epidermis, and it’s around <1mm thick even though it's made up of 5 distinct levels. The epidermis is made mostly of cells called Keratinocytes, which migrate up from the stratum Basale, the lowest level of the epidermis. As these cells move upwards, they become thinner & more mature. The maturity of the keratinocyte cells defines the nature of each level of the epidermis.
The 5 layers of the epidermis, from top to bottom, are:
This is the uppermost layer of the Epidermis and consists of dead keratinocytes. In this layer, the cells are filled with keratin, the same tough protein that makes up your hair and nails. The stratum corneum acts as a protective barrier.
A thin layer of dead skin cells helps the skin stretch and resist friction damage, particularly around the soles of your feet and palms.
The middle layer of the epidermis, consisting of flat Keratinocytes that have no nuclei or centre. When doctors measure melanomas to see how far they’ve penetrated, known as the Breslow thickness, these measurements start from The Stratum Granulosum.
A layer of spiny cells that gives your skin its strength.
The deepest part of the epidermis where cells (keratinocytes) replicate and begin their journey upwards. This layer also contains melanocytes, the cells that produce melanin to determine skin colour.
When skin cells, Keratinocytes, are abnormal, it’s a sign of cancerous or pre-cancerous conditions such as Solar Keratosis, Intraepithelial Carcinoma & Squamous Cell Carcinoma. There are also several other parts of the human epidermis that may be included in your skin pathology report.
Melanocytes are the pigment-producing cells found in the Stratum Basale. There are around 15 keratinocytes in your epidermis to one melanocyte. Melanocytes produce melanin, which gives you your skin colour and is taken up by keratinocytes. So one melanocyte supplies around 15 Keratinocytes with melanin. If you have abnormal melanocytes, then it may be a sign that you have melanoma.
Rete Ridges are downward projections of the epidermis into the dermis, the second layer of skin.
Merkel Cells are found in groups in the Basal Layer of the epidermis. They connect to nerves from the dermis and help transmit the sensation of touch. Very occasionally, they can develop into Merkel Cell Cancer.
Langerhans Cells are found mainly in the epidermis and the upper part of the dermis. They participate in immune function by detecting foreign cells such as bacteria and other antigens.
The Dermis is the thickest part of your skin, and it’s found underneath your epidermis, so you can’t see it unless you’re wounded. The dermis is divided into two sections:
- The upper Papillary dermis
- The lower Reticular Dermis
While it’s always tough and flexible, the dermis is thicker on different parts of your body. For example, on your back, it’s around 7-8mm thick, but on your eyebrows, it’s around 1mm thick.
The dermis also extends up into the epidermis in finger-like protrusions called Dermal Papillae. These help keep the dermis and epidermis together and also contain superficial dermal blood vessels to help nourish the epidermis.
When you have a skin biopsy, your doctor will always take a sample of the epidermis and often part of the dermis as well. There are two main reasons for this.
Firstly, it’s very hard to take a sample of the epidermis alone. It’s incredibly thin and varies from person to person and body part to body part. So, trying to take a shallow sample like this is nearly impossible.
Secondly, and more importantly, the dermis makes up the bulk of the skin. This is where your doctor needs to look for deeper skin cancers.
Superficial biopsies of the skin can miss these deeper cancers or result in the cancer not being staged correctly. And this could result in an incomplete skin cancer pathology report and be very dangerous for your long-term recovery.
Melanin causes the pigment or colour in your skin.
When cells like keratinocytes and melanocytes have more melanin, it causes:
- Lentigo (an age spot or simple freckle)
- Lip freckles
- Pigmented solar keratosis, which is a rough, scaly patch that’s found on sun-exposed skin
- Cancers (pigmented Bowens, pigmented BCC)
- Inkspot lentigo, a dark spot with uneven edges
- Seborrhoeic Keratosis, a noncancerous skin growth that tends to be rough, scaly, and brown, black, or tan
- Acanthosis – these are dark patches of thickened skin, e.g. Clear Cell Acanthoma / Large Cell Acanthoma.
Full-thickness atypia = the entire epidermis is filled with abnormal keratinocytes (e.g. Intraepithelial carcinoma).
- Parakeratosis – this is when the keratinocytes in the Stratum Corneum or top layer of the epidermis keep their nuclei
- Melanocytic Proliferation – when you have more Melanocytes than normal, such as when you have lots of moles or melanoma.