Conjunctival melanoma is a rare yet aggressive form of eye cancer, developing on the conjunctiva, the clear membrane covering the white part of the eye and the inner surfaces of the eyelids. This malignancy poses a significant health risk, with potential for local tissue invasion and spread to other parts of the body. Early identification is important, as it can be life-threatening if not properly managed. This type of melanoma represents approximately 2% of all eye tumors and about 0.25% of all melanomas in the body.
What is Conjunctival Melanoma?
Conjunctival melanoma originates from melanocytes, pigment-producing cells in the conjunctiva. This condition is uncommon, with an estimated incidence ranging from 0.2 to 0.8 cases per million people each year. The incidence appears to be rising, mirroring trends seen in skin melanoma, which suggests a connection to ultraviolet (UV) light exposure. It may arise de novo (spontaneously, accounting for about 15-25% of cases) or evolve from benign precursor lesions.
Primary acquired melanosis (PAM) is a common precursor, accounting for up to 75% of conjunctival melanomas, particularly PAM with atypia, which involves abnormal melanocytes. Conjunctival nevi (moles on the eye) can also transform into melanoma, though this is less common, occurring in less than 10% of cases. While nevi are usually present from childhood and may contain cysts, PAM typically appears as a flat, acquired pigmentation in adulthood. Melanomas arising de novo are associated with a higher risk of metastasis and a less favorable prognosis compared to those originating from PAM or nevi. UV exposure is a risk factor, particularly in fair-skinned individuals, where the incidence of conjunctival melanoma is higher.
Recognizing and Diagnosing Conjunctival Melanoma
Conjunctival melanoma can present with varied appearances, making its recognition and diagnosis challenging. While it often appears as a pigmented, raised lesion, it can also be amelanotic (lacking pigment), appearing pinkish or reddish. These amelanotic forms are difficult to diagnose, as they may be mistaken for common conditions such as conjunctivitis or benign inflammatory processes like pyogenic granuloma.
Signs include a new pigmented spot on the eye, a spot that changes in size or color, or the presence of prominent feeder vessels. The lesion may be flat or nodular and is usually unilateral. While often painless, some individuals may experience eye discomfort or irritation.
A definitive diagnosis requires a biopsy, where a tissue sample of the suspected lesion is removed and examined under a microscope by a pathologist. This histopathological evaluation confirms the presence of cancerous cells and determines disease extent. Imaging studies, such as optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM), provide additional information about the lesion’s thickness and extent, helping to differentiate it from other conditions and assess for deeper invasion. These are supplementary tools to the biopsy. It is also important to distinguish conjunctival melanoma from other pigmented lesions like conjunctival nevi (which often contain cysts) or primary acquired melanosis (PAM) without atypia (a flat, non-cancerous pigmentation).
Treatment Approaches
The primary treatment for conjunctival melanoma is surgical excision, aiming to remove the tumor completely. This involves excising the lesion with wide margins (typically 2 to 4 millimeters of healthy tissue) to ensure all cancerous cells are removed. For larger or more diffuse lesions, a “no-touch technique” may be employed during surgery to minimize manipulation of the tumor and reduce the risk of spreading cancer cells.
Following surgical removal, adjuvant therapies are frequently used to reduce the risk of local recurrence and systemic spread. Cryotherapy, which involves freezing the edges of the surgical site, is a common adjuvant treatment to destroy remaining microscopic cancer cells. Topical chemotherapy, such as mitomycin C, may be applied to the eye surface, especially for cases with residual intraepithelial disease or diffuse primary acquired melanosis (PAM). Radiation therapy, including brachytherapy (placing radioactive sources near the tumor) or external beam radiation, can also be considered, particularly for tumors with deep margins or those that are difficult to excise completely due to their location.
For advanced or metastatic melanoma, systemic therapies may be considered. These include immunotherapy, which helps the body’s immune system fight the cancer, and targeted therapy, which focuses on specific genetic mutations within the cancer cells. These systemic treatments are often repurposed from cutaneous melanoma treatments, given the similarities in their clinical behavior and metastatic patterns. Their use for conjunctival melanoma is still evolving and typically reserved for more complex or widespread cases.
Prognosis and Long-Term Care
The prognosis for individuals with conjunctival melanoma varies, influenced by several factors. Tumor thickness and the presence of ulceration on the tumor surface are significant indicators, with thicker and ulcerated lesions generally associated with a less favorable outlook. The location of the tumor on the conjunctiva also plays a role; lesions in the caruncle or palpebral conjunctiva (inside the eyelids) may carry a higher risk for metastasis and local aggression compared to those on the bulbar conjunctiva (white part of the eye). The origin of the melanoma can also impact prognosis, with de novo melanomas often associated with worse outcomes than those arising from primary acquired melanosis (PAM) or nevi.
Metastasis, or the spread of cancer, is a concern. Conjunctival melanoma commonly spreads through the lymphatic system to regional lymph nodes, such as those in front of the ear or under the jaw. From there, it can spread to distant organs, including the lungs, liver, soft tissues, bone, and brain. Sentinel lymph node biopsy may be considered to assess for regional spread. The 5-year disease-specific mortality rates range from approximately 14% to 27%, while 10-year rates can be between 25% and 35%.
Given the risk of local recurrence and distant metastasis, long-term, regular follow-up examinations are important. This typically involves thorough eye examinations and periodic imaging of regional lymph nodes. Additional systemic imaging, such as chest radiographs or abdominal/chest CT scans, may be recommended based on clinical findings. A multidisciplinary approach, involving ocular oncologists, medical oncologists, and other specialists, is often necessary to manage the condition over time and provide comprehensive care.