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Pathology of Uveal Melanoma

Dr Sampurna Roy MD

 

  

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Uveal melanoma is a rare tumour, however, it is the most common primary intraocular malignancy in adults. It may arise from melanocytes in any part of the eye.

The tumour is usually seen in the iris, the choroids and ciliary body.

Risk Factors:

- Age: median age at presentation is 53 years.

- Race: more frequently seen in Caucasians, particularly blue-eyed, blonde individuals.

- Genders:  slightly more in men.

- Geographic variations:  Higher incidence is seen Scandinavian countries than Africa suggesting that sunlight exposure is not a risk factor.

- Genetics:  Genetics is not well defined. Familial cases may show chromosome abnormalities (trisomy 8 and monosomy 3 and 6).

- Predisposing lesions: There is no established predisposing lesions which may increase the incidence.

Clinical presentation:

Clinical presentation depends on:

- i) Location of the tumour : Tumours of the posterior pole causes early symptoms.

- ii) Clinical stages:

       -Stages I and II represent the early stages. These may be asymptomatic or with symptoms related to loss of vision.

       -Stage III shows ocular symptoms such as increased intraocular pressure, inflammation and pain.

       -Stage IV shows symptoms of extraocular extension such as proptosis, subconjunctival mass.

- iii) Tumour size:   It is classified according to the largest tumour dimension ; Small tumours are discoid shaped and less than 10 mm in the largest dimension ; Medium and large tumours show collar stud or mushroom-shaped appearance ; Large tumours are over 15mm in size.

 -iv) Other clinical parameters:

   - Spread of tumour to extrascleral site.

   - Tumor margin located anterior to the equator of the eye.

   - Tumor-induced glaucoma.

Pathology:  

The tumour is classified into two main cell types:  Spindle and epithelioid.

Spindle cells are highly cohesive fusiform cells with small nuclei. Small tumours seen in early stages of disease are composed of these well- differentiated melanocytes.   Histopathology Image

Epithelioid cells are large polyhedral cells with abundant cytoplasm and contain large nuclei with round nucleoli. 

In some cases multinucleated epithelioid type cells are present. These poorly differentiated melanocytes indicate aggressive nature of the tumour.

Immunohistochemical profile: 

HMB-45 (most specific) ; S-100 protein ; Neuron-specific enolase (NSE).

Differential Diagnosis:

Metastatic carcinoma ; Schwannoma ; Neurofibroma

Radiology:

- Ultrasonography A and B scans are the most accurate method for diagnosis and to determine the tumour size .

- Computed tomography and Magnetic resonance imaging are useful in the diagnostic evaluation.

Prognostic factors:

- Tumour size and location (most important prognostic factors)

- Extraocular extension.

- Other clinical parameters: (i) tumor margin anterior to the equator of the eye  (ii) older age (iii) male (iv)  tumour induced glaucoma.

Metastasis, treatment and survival:

Uveal melanoma metastasize hematogenously and preferentially to the liver.

Metastasis can occur any time up to 20 years after treatment. 

Aside from hematogenous spread, uveal melanomas disseminate by traversing the sclera to enter the orbital tissues, usually at sites where blood vessels and nerves pass through the sclera.

 Unlike melanomas of the skin, those of the uvea do not exhibit lymphatic spread, because the eye lacks lymphatics.

Intra-ocular melanomas secondarily cause hemorrhage, cataract, glaucoma, retinal detachment, and inflammation. Each of these manifestations may mask the basic pathologic disorder.

Treatment depends on the size of the tumour .

1. Small tumours:   If no further growth is seen no treatment is undertaken ;  If the tumour grows radiation is applied ;  If the tumour continues growing enucleation is performed.

2. Large tumours:   Follow up with liver function tests is performed to ensure that there is no metastasis. Even with treatment there is no significant change in survival.

Life expectancy is 2 to 7 months after detection of metastasis.

Surgical resection of hepatic metastasis coupled with chemotherapy is the best method of improving survival.

Choroidal Melanoma:

The choroid is the most common site. Choroidal melanomas are usually circumscribed and invade Bruch's membrane, causing a collar stud  or mushroom-shaped mass.

By contrast, some are flat (diffuse melanoma) and either cause a gradual visual deterioration over many years or not become apparent until extra-ocular or distant dissemination has occurred.

Orange lipofuscin pigment is evident over the surface of some choroids melanomas.

Based on the microscopic appearance of uveal melanomas, they have been subdivided into different types spindle A, spindle B, fascicular, necrotic, mixed, and epithelioid types).

Histological study of choroidal malignant melanoma treated by carbon ion radiotherapy.

Melanomas of the Ciliary body and Iris:    

Melanomas of the ciliary body and iris may extend circumferentially around the globe ("ring melanoma").

Melanomas in the iris present clinically one or two decades earlier than those in the choroids and ciliary body, perhaps because they are more easily seen.

Clinical signs and differential diagnosis of iris melanoma .  

Conjunctival Melanoma

Occasionally, one or more irregular areas of pigmentation appears spontaneously in a non-pigmented portion of the conjunctive of one eye at about 40 to 50 years of age.

This condition, designated primary acquired melanosis, is analogous to the lentigo-maligna variety of melanoma in the skin and may regress spontaneously or evolve into a malignant melanoma.

Other malignant melanomas of the conjunctive are preceded by a nevus, or have no overt antecedent lesion. Some tumours represent an extension of an intra-ocular melanoma.

 

Further reading

Clinical Characteristics of Uveal Melanoma in Patients With Germline BAP1 Mutations.

Presence and phenotype of dendritic cells in uveal melanoma.

Optic nerve invasion of uveal melanoma.

Bruch's membrane abnormalities in dome-shaped and mushroom-shaped choroidal melanomas.

Multiple locations on chromosome 3 are the targets of specific deletions in uveal melanoma.

Lymph node metastases arising from uveal melanoma.

 

 

 

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Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


 

 

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