THE SKIN

The skin has two main layers: the epidermis and the dermis. The epidermis is the outer layer of the skin and has the main functions of waterproofing us and controlling our body temperature. The dermis is the strength part of the skin (the part of animal skins that gets turned into leather) and can resist the many daily knocks and bumps that we experience. The epidermis and dermis are separated by a very thin but very strong membrane called the basement membrane. This is a very important structure when it comes to understanding melanoma.

Human skin diagramThe epidermis, itself, is divided up into several layers. The bottom (or basal) layer contains the cells (basal cells) that are constantly dividing to replace dead skin cells that are lost from the surface. Scattered amongst the basal cells are large flat cells with multiple extensions called melanocyctes. Melanocyctes are our tanning cells. When stimulated by ultraviolet light, enzymes within the melanocyctes are activated to produce melanin pigment which is then transferred to the new cells that are being produced in the basal layer. The melanin pigment is positioned around the nuclei of the new cells and performs the function of absorbing ultraviolet radiation from the sun and thus protecting the cell’s DNA from damage.

Of interest is that the stimulus for melanin production is actually damage to melanocyte DNA. So having a tan signifies that damage has occurred to the DNA of one’s skin cells.

SOME BACKGROUND ABOUT CANCER

A cancer occurs when a cell starts to divide uncontrollably and no signal is given for this to stop. The sort of cancer that results depends on what sort of cell becomes cancerous. If it was a cell in the lining of the lung then lung cancer results. If it was a cell lining the colon then colon cancer results. If a melanocyte becomes cancerous it results in a melanoma. Every different sort of cell in the body can potentially become cancerous.

The behaviour of each sort of cancer depends on what sort of enzymes the specific cancer cells are able to produce. Some cancers only produce enzymes that result in destruction of the tissues around them. Others have enzymes that enable them to bore holes into blood vessels and lymphatic channels. This gives them access to the circulation and the lymphatic system and allows them to spread to one’s organs or to one’s lymph glands. When cancer spreads like this it is known to have metastasized.

What causes cancer?

We all have cancer genes in the DNA of our cells, the purpose of which is not yet known. These cancer genes are kept switched off when cells are functioning properly but if a cell’s DNA becomes damaged (by cigarette smoke or by ultraviolet light, for example) in a sensitive area a cancer gene may become activated. If this happens, that cell turns into a cancer cell and starts to multiply uncontrollably. The main cause of melanomas is damage to one’s skin by ultraviolet light from the sun. The ultraviolet light penetrates the DNA in the melanocytes causing damage. If this damage results in a cancer gene becoming active a melanocyte turns cancerous resulting in a melanoma.

THE LYMPHATIC SYSTEM

Seventy percent of the body is composed of water. As blood is pushed through the capillaries (the smallest blood vessels) the pressure causes some of the water in the blood to be squeezed out of tiny pores in the wall of the blood vessels into the surrounding tissues. If this water were not collected and transported back to the heart one’s arms and legs would become massively swollen within a day. To prevent this from happening there are multiple water channels (lymphatic channels) within the tissues (particularly the skin) that collect the excess water and carry it back to the heart.

At certain points the water channels pass through lymph glands (nodes) which filter the water that passes through them. Any bacteria, foreign material or cancer cells that are carried with the water in the lymphatics also enter the lymph glands and are trapped there. Lymph glands are full of antibodies and immune cells which then proceed to attack anything that is perceived to be a threat. The lymph glands are concentrated in certain parts of the body: the groin, axilla (arm pit) and neck.