Melanoma is a type of  cancer arising from damage to the DNA in melanocytes – most commonly in the skin.  As such, there is uncontrolled growth (and function) of melanocytes.  Initially, the melanocytes, which normally reside near the basement membrane, will grow towards the skin surface (pagetoid spread) – thus keeping the basement membrane in tact.   To the naked eye, melanoma will look like a dark, irregular looking mole (see later section on early detection), which indicates the increased amount of melanocytes and/or melanin. However, eventually, the tumour will grow past the basement membrane and invade the dermal layer (papillary layer). Once into the papillary layer of the dermis there are no barriers to moving into the deeper layers of the dermis.  The reticular dermal layer contains larger blood  and lymphatics vessels – sites where melanoma cells can can enter and spread via metastasis.

When melanoma spreads to distant organs, the cancer – with all of its properties – continue their growth and production of melanin.  Signs and symptoms of melanoma will be more recognizable as the growth of the tumour may compress delicate structures (e.g. brain, pulmonary airways and vessels) and/or the presence of melanin is visibly noticed or found to interfere with the organ’s function (e.g. brain, kidney).

^{Progression of Melanoma by Lyz Boyd, licensed under CC-BY-NC}

Section Review

• Melanoma appears as an abnormal collection of melanocytes which is visibly noted by a localized darkening of skin (i.e. abnormal mole) of abnormal size, shape, and variety of colours – all of which is indicative of the uncontrolled growth and localized spread of melanocytes.
• If the uncontrolled growth of melanocytes break through the basement membrane of the epidermis, these abnormal  melanocytes can be in close proximity to blood and lymphatic vessels that reside in the dermis & hypodermis.  Upon entering these vessels, melanoma can spread (metastasize) to distant organs.

Review Questions