What Are Metastatic Optic Tumors?
The tumors that are formed in the eye as a result of metastasis are known as metastatic optic tumors. Metastasis is a process by which cancer cells spreads from the affected organ to other parts of the body, and when this happens to the eye, it is known as ocular metastasis. Ocular metastasis can be divided into:
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Intraocular Metastasis- It is when cancer spreads to the intraocular structures (uveal tract, lens, aqueous humor, retina, vitreous body, etc.) of the eye.
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Extraocular Metastasis- In this phenomenon, cancer spreads to the extraocular structures (orbit, conjunctiva, lacrimal system, eyelids, etc.) of the eye.
The most common form of ocular metastasis is intraocular metastasis and the source for it is the primary cancer of breasts in women and lungs in men, less common sources include the gastrointestinal tract, prostate, lymphoid, leukemia, thyroid, kidney, and skin.
Irrespective of their prevalence, metastatic optic tumors often get undetected because most ocular metastases are occult, asymptomatic, and do not cause loss of vision. They only become a concern when they affect vision, push the eye forward (proptosis), or are visible to the patient.
The frequent intraocular structure for metastasis is the choroid (choroidal metastasis) of the eye due to its abundant vascular supply. Choroidal metastasis occurs in up to ten percent of patients with systemic metastatic diseases (more than one organ) and is often asymptomatic.
However, ocular metastasis can affect the macula, optic nerve, or the anterior segment of the eye, resulting in vision loss and painful glaucoma. Prompt treatment with external beam radiation is the best chance for retention of the vision and the eye, but the clinician should also determine the primary source of metastasis to prevent a recurrence.
What Causes Metastatic Optic Tumors?
Metastases to the eye are a rare occurrence because most cancers in the body spread through the lymphatic system which is absent in the eye. The only way for cancer cells to reach the eye is through the hematogenous (blood) spread.
The ocular structures with the best vascular supply are the most likely ones to be affected, this includes the uveal tract-containing the choroid, the ciliary body, and the iris, followed by the retina and sclera.
The metastatic optic tumors are derivatives of primary cancers, hence they are identified by their source, the different primary cancers that have been known to cause orbital metastasis are-
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Breast cancer.
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Bronchogenic cancer.
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Gastrointestinal adenocarcinoma.
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Thyroid carcinoma.
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Renal cell carcinoma.
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Neuroblastoma.
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Ewing sarcoma.
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Wilms tumor.
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Leukemia.
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Pancreatic adenocarcinoma.
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Endometrial carcinoma.
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Ovarian carcinoma.
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Melanoma.
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Urothelial carcinoma.
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Non-Hodgkin lymphoma.
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Seminoma of the testis.
What Are the Symptoms of Metastatic Optic Tumors?
The most common symptom is reduced visual acuity, other presenting symptoms are-
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Diplopia (double vision).
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Photophobia (eye discomfort in bright light).
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Ptosis (drooping of the upper eyelid over the eye).
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Blepharitis (inflammation of the eyelids).
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Metamorphopsia (visual distortion in which straight lines appear curved).
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Pain.
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Flashes and floaters.
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Mass lesion.
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Uveitis (a form of eye inflammation).
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Exophthalmos (bulging or protruding of eyeballs).
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Secondary glaucoma.
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Detached retina.
How Are Metastatic Optic Tumors Diagnosed?
Most patients with metastatic optic tumors have a known primary cancer and metastatic tumors in other parts of the body, careful medical history can uncover the signs and symptoms and if the ocular oncologist (eye cancer specialist) suspects ocular metastasis, they should examine both the eyes and orbits because ocular metastasis can be both bilateral and multifocal.
The patient should also be examined by an oncologist (cancer specialist) so that a complete metastatic survey is performed, this will detect other tumors in the body and also “stage” the patient.
After examination, the clinician will request any of the following investigations-
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Photography - It is an important tool in the management of metastatic optic tumors. These tumors grow rather quickly, hence documentation regarding their size and location will help the clinician understand their growth rate, this also helps them to select the appropriate time for treatment.
A slit lamp camera is used for anterior segment tumors and specialized fundus autofluorescent (FAF) imaging is used to detect small multifocal tumors. Apart from these, intraocular angiograms are also used to determine the circulation pattern of the tumors.
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Ultrasonography - It is used to evaluate the origin of metastatic orbital tumors, for example, intraocular metastases from breast cancer or lung cancer have a characteristic variable internal reflectivity that helps distinguish them from melanoma and hemangioma.
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Computed Tomography (CT) - It helps to determine the cancer present within the bones that make up the orbit (the eye socket is made up of seven different kinds of bones).
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Magnetic Resonance Imaging (MRI) - Helps to identify inflammation and compression of the optic nerve that is caused by the tumor. A subdivision of this technique is the MRA (magnetic resonance angiography), which is particularly useful to identify orbital vascular tumors and abnormalities.
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Positron Emission Tomography (PET) - This imaging technique can evaluate the metabolic activity of tissues and is often combined with CT for initial tumor staging, evaluation of metastases with no known primary, and for rare ocular metastases.
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High-frequency Ultrasound Imaging - When metastatic tumors extend into the front of the eye they cause thickening of the anterior uvea, anterior rotation of the iris, enlargement of the ciliary body, etc. High-frequency ultrasound imaging is the only to observe these changes.
What Is the Treatment for Metastatic Optic Tumors?
The goal of the treatment is to restore the vision and there is a wide range of treatment options that can achieve it. The choice depends on the origin of primary cancer, its extent, the location of the metastasis, the patient’s well-being, and life prognosis.
The chemotherapeutic agents used in breast and lung cancer are also effective for ocular metastases, a few examples are Tamoxifen, Anastrozole, Letrozole, etc. This effectiveness is one of the reasons why screening fails to detect ocular metastasis. The patient with a known primary cancer will be receiving chemotherapy for it which will also regress the metastatic optic tumors making them unnoticeable.
However, the downside of chemotherapy is its slow rate of regression, this is attributed to the blood-ocular barrier, which is a physical barrier between the local blood vessels and most parts of the eye. It stops substances including drugs from traveling across it.
Because of this, the next preferable treatment modality is radiotherapy, photodynamic therapy (PDT) to be exact. It is performed using the standard TAP (treatment of age-related macular degeneration with photodynamic therapy) protocol - 600 milliWatt per centimeter square delivered over 83 seconds followed by intravenous Verteporfin infusion. The visual activity gets rapidly restored over the next six weeks to eight weeks but the long-term complications of this therapy include optic neuropathy and radiation retinopathy.
Conclusion:
Metastatic optic tumors are relatively common malignancies seen in the adult population. Occular metastasis that causes these tumors is considered a poor prognostic sign for the underlying primary cancer because the former is only seen when the latter has disseminated to the other parts of the body. But with the recent advances in cancer treatment, it is imperative that attention be paid to ocular metastases which will become more prevalent with increasing long-term survival rates in cancer patients.
