Choroidal melanoma is a rare type of eye cancer that originates in the choroid, a layer of blood vessels and connective tissue in the back of the eye. This condition represents the most common primary intraocular malignancy in adults.
What is Choroidal Melanoma?
The eye’s middle layer, known as the uvea, includes the iris, ciliary body, and choroid. The choroid is a dark layer underlying the retina, rich in pigment-producing cells called melanocytes. Choroidal melanoma develops when these melanocytes become malignant and grow in this vascular layer.
It is rare, with an incidence of about 5 to 10 cases per million people each year. Most choroidal melanomas appear as dome-shaped tumors, which can range in color from darkly pigmented to entirely non-pigmented. While they can remain asymptomatic for a period, their growth may eventually lead to visual disturbances.
How Choroidal Melanoma is Diagnosed
Detecting choroidal melanoma often begins with a comprehensive eye examination, including indirect ophthalmoscopy, where a specialist looks into the dilated pupil. This initial assessment can reveal the presence of a suspicious lesion. Further characterization of the tumor relies on various non-invasive imaging techniques.
Ultrasound, specifically B-scan and A-scan ultrasonography, is a primary tool used to measure tumor dimensions, assess its shape, and determine its internal structure. Optical Coherence Tomography (OCT) provides detailed cross-sectional images of the retina and choroid, helping to identify subretinal fluid or changes in the retinal pigment epithelium overlying the tumor. Fluorescein angiography and indocyanine green angiography may also be used to visualize the tumor’s vascularity and differentiate it from other conditions. Early detection of these tumors is important for effective management.
Treatment Options for Choroidal Melanoma
Managing choroidal melanoma involves various approaches, often selected based on tumor size, location, and other characteristics. One common eye-sparing treatment is plaque brachytherapy, which involves surgically attaching a small radioactive disc, or plaque, directly onto the sclera over the tumor site. This plaque delivers a concentrated dose of radiation directly to the tumor while minimizing exposure to surrounding healthy tissues. The plaque typically contains radioactive seeds, such as iodine-125 or cesium, and remains in place for several days before being surgically removed.
Another external beam radiation therapy option is proton beam therapy, which precisely directs a high-energy beam of protons to the tumor. This method allows for targeted radiation delivery, making it suitable for certain tumor sizes and locations. For very small tumors, local resection or laser photocoagulation might be considered to destroy the cancerous cells. In cases where tumors are very large, or other treatments are not suitable, enucleation, the surgical removal of the eye, may be necessary. The decision to pursue a specific treatment is carefully made by a multidisciplinary team to achieve tumor control while aiming to preserve vision and the eye whenever possible.
Understanding Prognosis and Curability
While local control of choroidal melanoma is often successful with current treatments, a primary concern is the potential for metastatic spread, especially to the liver. The liver is the most common site for these secondary tumors, occurring in up to 90% of patients who develop metastatic disease.
Several factors influence the prognosis, including the tumor’s size and location within the eye. Larger tumors and those involving the ciliary body are associated with a less favorable outlook. Genetic features of the tumor, such as mutations in the BAP1 gene, can also indicate a higher risk of metastatic disease, while EIF1AX mutations are linked to a lower risk. Even with successful local treatment, a lifetime risk of metastatic disease remains for some patients. Early detection and effective local treatment significantly improve outcomes, yet ongoing monitoring is necessary due to the potential for distant spread.
Life After Treatment: Monitoring and Follow-Up
Regular eye examinations are conducted to monitor the treated eye for any signs of local recurrence and to assess the health of the unaffected eye. These follow-up eye exams often involve the same imaging techniques used for diagnosis, such as ophthalmoscopy, ultrasound, and OCT, to track any changes.
Beyond ocular monitoring, systemic screenings are a routine part of follow-up care due to the risk of metastasis. This typically includes periodic imaging of the liver, such as ultrasound or MRI, and blood tests to check liver function.