In the later stages of cancer, tumor cells can invade different parts of the body. This is a process called metastasis. One part of the body is a rare victim of metastasis. These organs are the eyes. In what way does cancer traverse the body and reach our eyes? In addition, which types of diseases can it cause? These are the questions that scarce research is trying to answer. Because of its rarity, not enough studies focus on the relationship between cancer metastasis and the eyes. We will explore this subject with limited resources from decades ago to today.
Ocular Cancer and Its Causes
The rarity of ocular cancer comes from the fact that it mostly affects certain types of individuals. The risk factors for ocular cancer are often genetic or congenital. This includes the color of the eyes and the skin or a certain genetic mutation in one’s genes.
Uveal melanoma is a type of ocular cancer commonly affecting those with blue eyes and fair skin. Genetic factors, such as the CLPTM1L locus also come into play. Other risk factors include sun exposure, tanning, and outdoor activities.
In the West, only six to eight persons per one million of the population acquire the disease. However, around 40% of people who acquire this disease will probably die. In general, ocular melanoma occurs 30% more often in women than in men.
Although having a high mortality rate, the prognosis for the disease has remained unchanged. This leads to a large number of deaths since the disease worsens while undetected. Additionally, doctors require a systemic prognosis to detect the disease. This means that they need to assess most parts of the body. If left untreated, uveal melanoma can also cause problems for the liver.
The other relatively common ocular cancer is retinoblastoma. This cancer occurs mostly because of a mutation in the RB1 gene. When cells lose this tumor suppressor gene, their replication becomes uncontrolled. This results in retinoblastoma.
While this can occur in adults, one-third of those with retinoblastoma are infants. They inherit the disease from their parents and develop rose-like figures in their eyes. These are rosettes or florets that consist of tumors forming in the eye.
Treatment efforts for retinoblastoma have been a success throughout developed countries. In recent years, therapies can now reduce the formation of the florets or rosettes in retinoblastoma. These therapies include brachyradiotherapy and intra-arterial chemotherapy.
Cancer Metastasis to the Eyes
If you are familiar with oncology, you would have noticed that melanoma is a term related to skin cancer. If you can remember, uveal melanoma has risk factors relating to sun exposure and skin color. As it turns out, skin cancer has associations with some ocular cancers.
Scientists have had some basis for this relationship since 1998. This article states that skin melanoma is one of the primary cancers leading to ocular cancer. Specifically, melanoma can cause metastasis in the retina.
Metastasis may occur in different sources of primary cancer. These are the specific primary cancer metastasis affecting different regions of the eye:
- Iris metastasis: due to breast carcinoma, lung carcinoma, sarcoma, and skin melanoma.
- Choroidal metastasis: due to breast and lung neoplasm in women or lung and gastrointestinal neoplasm in men.
- Retinal metastasis: due to lung carcinoma, skin melanoma, breast carcinoma, gastrointestinal carcinoma, and uterine cancer.
- Vitreous metastasis: due to cutaneous melanoma and large-cell lymphoma.
- Eyelid metastasis: due to lung, breast, and renal cell carcinoma, as well as melanoma.
- Optic disk metastasis: due to other ocular metastases.
- Conjunctival metastasis: due to other ocular metastases.
- Orbital metastasis: very rare metastasis occurring from several primary cancers.
From these primary sites, we can see how most contain the word carcinoma. This is because the epithelial tissues that these cancers affect play a crucial role in metastasis. In addition, these tissues cover the organs and passages of the body.
Cancer and Ocular Diseases
We have discussed the effect of other cancers on ocular cancer. Now, we will talk about the effects of cancer on ocular diseases. The similarities between the skin and the eyes are one to focus on. This is because both contain melanocytes that produce pigments that absorb light. This can lead us to some correlational studies.
In a 2021 study conducted in South Korea, a cohort database consisted of data from 2002 to 2015. Researchers investigated this data from over 1 million individuals regarding skin cancer and ocular cancer. They found that skin cancer has a significant association with ocular comorbidities such as macular degeneration.
Additionally, melanoma and retinopathy correlate with one another. Melanoma-associated retinopathy involves an abnormal response of the immune system to cancer cells. This can lead to patients having visual distortions and night blindness.
Other cancers, such as small-cell lung carcinoma, correlate with retinopathy. Scientists think that cancer-associated retinopathy may be an autoimmune condition. If the disease worsens, it can cause photoreceptor degeneration, leading to loss of vision.
Cancer is not only related to retinopathy. Other ocular diseases associated with cancer include cone dysfunction and bilateral diffuse uveal melanocytic proliferation. Cone dysfunctions can cause reduced central vision and color abnormalities. On the other hand, bilateral diffuse uveal melanocytic proliferation leads to a progressive loss of vision.
Ocular Cancer Treatment Advancements
Since most of these diseases are genetic, researchers are looking to use stem cells for treatment. Stem cells are the very foundation from which all other cells arise. It has an incredible capacity for self-renewal and regeneration. Thus, we can utilize this capacity to treat degenerative disorders in the body.
Scientists have described extensive research on stem cells in the book “Cancer Stem Cells: New Horizons in Cancer Therapies”. In the chapter on ocular cancer, they noted several stem cell markers on different eye tumors. Common markers include CD44, CD133, and SOX2. Researchers use these markers to identify and isolate stem cells for laboratory studies.
Since ocular cancer is one of the rarest cancers, it lacks focus in research and treatment. As such, scientists are still conducting further studies to specifically target ocular cancer cells. Right now, they are more focused on dealing with primary cancers that can cause ocular cancer.