Choroidal metastasis refers to a secondary cancer that has spread to the choroid layer of the eye from a primary cancer located elsewhere in the body. This condition occurs when cancer cells detach from an original tumor, travel through the bloodstream, and settle in the choroid.
The choroid is a highly vascular layer situated between the sclera, the white outer wall of the eye, and the retina, the light-sensitive tissue at the back of the eye. Its main function is to supply oxygen and nutrients to the outer layers of the retina, which are responsible for vision. This rich blood supply makes the choroid a common site for metastatic cancer cells to take hold and grow.
Primary Cancers and Associated Symptoms
Breast cancer is the most common source, accounting for 40% to 47% of cases, particularly in women. Lung cancer is another frequent primary site, responsible for 21% to 29% of choroidal metastases.
Other less common primary cancers that can spread to the choroid include those from the gastrointestinal tract, prostate, kidney, and skin melanoma. For about a quarter to a third of patients, choroidal metastasis is the first sign of an unknown primary cancer.
The presence of choroidal metastasis can lead to various visual symptoms, though some patients may initially experience no symptoms at all. Blurred vision is a common complaint, affecting most individuals. Patients might also notice floaters, which are small specks or strands that drift across their field of vision, or flashing lights, known as photopsia.
Visual field loss, appearing as a dark spot or shadow, can also occur, particularly if the tumor affects the central vision area. While less common, some individuals may experience eye pain or redness. These symptoms arise as the tumor grows and potentially causes fluid accumulation under the retina.
The Diagnostic Process
Confirming a diagnosis of choroidal metastasis involves a thorough examination by an ophthalmologist. The diagnostic process begins with a dilated eye exam, allowing the doctor to view the back of the eye and identify any suspicious lesions. This initial assessment can reveal yellow or white subretinal masses, which are characteristic features of choroidal metastases.
Several imaging techniques are used to further diagnose and characterize choroidal metastases:
Fundus photography documents the appearance of the back of the eye, capturing detailed pictures of the retina, optic nerve, and choroid to monitor changes over time.
Ocular ultrasound provides information about the tumor’s dimensions and internal structure. An A-scan measures the tumor’s thickness, while a B-scan creates a cross-sectional image of the eye, visualizing the tumor’s shape and its relationship to surrounding tissues. This non-invasive method helps differentiate metastatic tumors from other eye conditions.
Optical coherence tomography (OCT) offers high-resolution, cross-sectional images of the retina and choroid, allowing for detailed visualization of subretinal fluid and changes in the retinal layers caused by the tumor.
Fluorescein angiography involves injecting a dye into the bloodstream to highlight blood vessels in the eye, revealing patterns of blood flow that can distinguish metastatic lesions.
Due to the high accuracy of these imaging techniques and the potential risks involved, a biopsy of the eye tumor is rarely performed to confirm choroidal metastasis.
Treatment Approaches
Treating choroidal metastasis requires a collaborative effort involving an oncologist and an ophthalmologist. The treatment plan is customized for each individual, considering the type and extent of the primary cancer, the size and location of the eye tumor, and the patient’s overall health. The aim of treatment in the eye is to preserve vision and reduce local symptoms.
Local Eye Treatments
Local eye treatments focus directly on the tumor within the eye. External beam radiation therapy (EBRT) delivers radiation from an external source to shrink the tumor and control its growth. This method can be effective for larger or multiple tumors.
Plaque brachytherapy involves surgically placing a small radioactive disc, or plaque, directly onto the outer wall of the eye over the tumor. The plaque delivers a concentrated dose of radiation to the tumor while minimizing exposure to surrounding healthy tissues, and it is removed after several days.
Other localized therapies include photodynamic therapy (PDT) or laser photocoagulation. PDT uses a light-sensitive drug activated by a specific type of laser to destroy abnormal cells, while laser photocoagulation uses a focused laser beam to burn and destroy the tumor tissue. These methods are reserved for smaller tumors or specific situations.
Systemic Treatments
Systemic treatments are important for managing choroidal metastasis, as the eye tumor indicates that the cancer has spread throughout the body. These treatments target the primary cancer and any other metastatic sites, including the eye.
Systemic chemotherapy uses drugs that travel through the bloodstream to kill cancer cells throughout the body. Targeted therapy employs drugs that specifically attack cancer cells with certain genetic mutations or protein expressions. Immunotherapy, another systemic approach, helps the body’s own immune system recognize and fight cancer cells. The specific systemic treatment chosen depends on the type, stage, and molecular characteristics of the primary cancer.
Prognosis and Follow-Up Care
The overall prognosis for individuals with choroidal metastasis is determined by the status and progression of the primary cancer from which it originated. The presence of metastases to the eye indicates disseminated disease, meaning the cancer has spread beyond its initial site. Therefore, the long-term survival outlook is more closely tied to the response of the primary cancer to systemic treatments rather than the eye tumor itself.
Regarding visual prognosis, the goal of eye-specific treatments is to preserve as much vision as possible and prevent complications such as retinal detachment or severe vision loss. While treatment can stabilize or improve vision, the extent of recovery can depend on the tumor’s size, location, and the presence of any damage to the retina before treatment began. Early detection and intervention lead to better visual outcomes.
Following treatment for choroidal metastasis, regular and coordinated follow-up care is important. This care involves both the oncology team, who monitors the primary cancer and systemic disease, and the ophthalmology team, who continues to monitor the eye tumor and overall eye health. Frequent eye examinations, including imaging, are necessary to detect any recurrence or new lesions in the eye. This comprehensive approach ensures ongoing management of both the eye condition and the underlying systemic cancer.