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Uveal melanoma FAQs

What is uveal melanoma?

A uveal melanoma is a malignant tumour arising in the uveal tract of the eye.

 

What is 'uveal tract'?

The uveal tract comprises the choroid, the ciliary body and the iris. The choroid is cup-shaped and sandwiched between the retina and the sclera. The ciliary body is a ring of muscle lining the rim of the choroidal cup; it stretches the lens to adjust the focus of the eye. The iris is a muscular shutter that adjusts the size of the pupil thereby regulating the amount of light entering the eye. The uveal is composed of blood vessels and pigmented cells known as melanocytes, which are the cells giving rise to melanoma.

 

What is 'melanoma'?

Melanoma is a malignant tumour arising from melanocytes. More than 90% of uveal melanomas involve the choroid, the remainder being confined to iris and/or ciliary body.

 

What is 'tumour'?

A tumour is the medical word for 'lump'. Tumours can be neoplastic or non-neoplastic, according to whether new tissue is formed. Non-neoplastic tumours include cysts and other swellings such as bruises.

 

What is a 'neoplastic tumour'? 

A neoplastic tumour is formed by growth of new tissue. Such growth can be benign or malignant. A benign tumour tends to form a ball, which pushes against surrounding tissues as it grows. A malignant tumour also tends to invade adjacent tissues, by sending out 'roots', so to speak. Some but not all malignant tumours also scatter seeds, which disseminate elsewhere to form new tumours, known as 'metastases' (note: one 'metastasis' and many 'metastases'). When tumours disseminate in this way, they are said to 'metastasize'.  

 

How does uveal melanoma damage the eye?

Choroidal melanomas (that is, those affecting the choroid) tend to cause fluid to accumulate under the retina so that the retina becomes detached. This causes distorted vision, blurred vision, blind-spots in the peripheral vision and flashes of light ('photopsia').

Ciliary body melanomas tend to press on the lens, which becomes distorted and cloudy (i.e., develops cataract). Distortion of the lens causes ghosting or shadowing of images. Cataract causes blurring of vision and dazzle. They can also invade the anterior chamber and spread around the trabecular meshwork to cause glaucoma. The trabecular meshwork is the 'gutter' that drains fluid from the eye. It is located in the angle between the iris and the cornea. The cornea is the transparent window of the eye. Glaucoma is high pressure in the eye. It damages the optic nerve to cause tunnel vision and eventually total blindness of the affected eye.

Iris melanomas can be visible to the naked eye and can also cause cataract and glaucoma.

If a ciliary body or choroidal melanoma is not treated in time, it can become very large, causing severe disorganisation of the eye, with retinal detachment, inflammation (i.e., 'uveitis') and 'neovascular glaucoma' (i.e., glaucoma caused by new blood vessels, which develop on the surface of the iris and in the angle to block the gutter).

Uveal melanomas can also spread extra-ocularly, to form an orbital tumour or to become visible sub-conjunctivally. The orbit is the 'cave' in the skull, which houses the eye. It is filled with fat. The conjunctiva is the fine, transparent skin covering the white of the eye and the inner surface of the eyelids. If an orbital tumour is not treated, it can push the eye forwards and this bulging is called 'proptosis'. It can also spread backwards into the brain.

 

How do uveal melanomas threaten life?

Uveal melanomas can metastasize to the liver and other parts of the body. If very advanced they can invade the orbit, ultimately reaching the brain (although this is rare nowadays).

 

Which uveal melanomas metastasize?

Metastatic disease occurs almost exclusively in patients whose uveal melanoma shows monosomy 3. This abnormality is highly lethal.

 

What is monosomy 3?

Monosomy 3 is loss of chromosome 3, which can be partial or total. Partial loss means that only a segment of chromosome 3 is missing. Total loss means that the entire chromosome is lost.

 

What is a chromosome?

A chromosome is a worm-like structure, which contains coiled DNA, in which the genes regulating cellular behaviour are found. There are 23 pairs of chromosome, with each pair containing one paternal and one maternal chromosome (i.e., from the father and mother respectively).

 

Is monosomy 3 hereditary?

No, because it arises in the melanoma cells, which unlike sperm cells and eggs are not passed on to the next generation.

 

Is uveal melanoma hereditary?

Very, very rarely.

 

Does uveal melanoma spread to the other eye?

Very rarely.

 

Does uveal melanoma spread to brain?

Very rarely. When it does metastasize to the brain, it usually does so after the liver becomes diseased.

 

Is it possible to estimate the life-expectancy of a patient with uveal melanoma?

The life-expectancy can be estimated, very approximately, according to the genetic type of the melanoma, the size of the tumour, and the histological grade of malignancy.

As mentioned above, metastatic spread occurs almost exclusively in patients whose tumour shows monosomy 3.

The bigger the tumour (i.e., the more advanced the 'clinical stage') the longer it has been growing and the longer any metastases have been growing. Large tumour size also tends to indicate that the tumour is growing more quickly. Fast-growing tumours tend to be more dangerous.

Tumours with histological features of high-grade malignancy tend to be more dangerous. Histology is the examination of tissues under a microscope. Melanomas of low-grade malignancy tend to be composed of spindle cells (i.e., melanoma cells having a long and narrow shape) and to show few dividing cells (i.e., few 'mitoses'). Melanomas of high-grade malignancy tend to show epithelioid cells (i.e., large, round melanoma cells) and many mitoses. Melanomas tend to develop 'scaffolding' (i.e., 'stroma'), which in high-grade malignancy forms ring-shaped structures on microscopic examination and these are called 'closed loops'.

 

Mathematical programs have been developed for estimating the chances of metastatic disease and the likely survival time according to genetic type, clinical stage and histological grade of malignancy.

 

What causes uveal melanoma?

In most patients, no cause is found. Uveal melanomas are more common in patients with a fair complexion and light-coloured eyes and are very rare in black individuals. Uveal melanomas are also more common in those with an unusually large number of moles on their skin and in those who freckle and sunburn easily. The role of sunlight is, however, uncertain. There is no evidence that lifestyle changes can prevent the development of uveal melanoma, but perhaps such evidence might one day be revealed.

 

Some uveal melanomas arise from benign moles in the eye, particularly those known as 'melanocytoma'. Melanomas can also arise from 'congenital ocular melanocytosis' or 'Naevus of Ota', consisting of an increased population of melanocytes in the uvea, episclera, orbit, meninges (i.e., brain covering), and eyelid skin. There is also an association with a rare disease known as neurofibromatosis. Patients with these conditions therefore need life-long checkups, every year or so.

 

Are moles in the eye dangerous?

The prevalence of intraocular naevus is about one-in-ten, but the lifetime risk of uveal melanoma is less than one-in-two-thousand. Naevi can therefore be dis-regarded unless they show unusual features (i.e., if they are unusually large or show other suspicious features). It can be difficult or impossible to distinguish a large, benign naevus from a small, malignant melanoma unless growth is documented or unless biopsy is performed (which is easier said than done).