What types of tumors affect the eyelids, conjunctiva, and periocular tissues?
The eyelids and surrounding tissues (e.g., conjunctiva) are considered extensions of the skin. Therefore, the types of tumors that can develop in the skin can develop in these tissues too.
In general, tumors develop from the abnormal growth and unregulated replication of the cells that make up body tissues. The eyelids and surrounding tissues are made up of many kinds of cells. The edges of the eyelids, for example, have tiny glands, called meibomian glands, containing cells that produce secretions to lubricate the eye. If these cells overmultiply, they develop into benign tumors called meibomian gland adenomas (non-cancerous) or meibomian gland adenocarcinomas, a less common malignant tumor.
The edges of the eyelids also have melanocytes, cells that produce pigment. If these cells overmultiply, they will cause tumors called melanomas. And when skin cells (squamous) overmultiply, they cause squamous cell carcinomas (SCC).
Similarly, the conjunctiva contains lymphoid tissue cells, and if these overmultiply, they cause lymphomas or mast cell tumors.
There are other types of tumors that can affect the eyelids, conjunctiva, and periocular tissues, but the above are the most commonly diagnosed tumors.
What causes these types of tumors?
Why a pet may develop these types of tumors, or any cancer, is not straightforward. Very few cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Squamous cell carcinoma has been attributed to exposure to ultraviolet rays/sunlight. Breeds with light-colored haircoats and breeds that are hairless are especially at risk. Otherwise, the causes for these types of tumors are not clear.
What are the signs of these types of tumors?
The signs of these tumors can vary depending on the type of tumor, where it grows, and whether it is benign or malignant. Benign tumors tend to be polyp- or cauliflower-like in appearance. They may grow on the inside or outside of the eyelids. If they come into contact with the clear surface of the eye (the cornea), they can cause painful corneal scratches that can lead to corneal ulcers. They can also cause general irritation and inflammation leading to eye infections. Malignant tumors tend to be irregular or nodular in appearance. They may ulcerate (break open) and bleed, and become inflamed, infected, and painful.
Other signs that your pet may have a tumor of the eyelid, conjunctiva, or periocular tissue include:
- eye discharge
- protrusion of the third eyelid
- roughening/thickening of the conjunctiva
- repeated pawing or rubbing the eye
How are these types of tumors diagnosed?
Your veterinarian may use a procedure called fine needle aspiration (FNA) to make a diagnosis. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.
In some cases, when the results from FNA are not entirely clear or when surgical removal of the tumor is otherwise indicated, the entire tumor is removed and assessed to get a definitive diagnosis. The tumor is examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is not only helpful to make a diagnosis but can indicate how the tumor is likely to behave.
How do these types of tumors typically progress?
Depending on the type of tumor, its location, and whether it is benign or malignant, these types of tumors may be slow or fast growing and may or may not metastasize (spread elsewhere in the body). Tumors in the conjunctiva are likely to grow more quickly than tumors of the eyelids and tend to invade the surrounding tissue and spread to other sites.
"Depending on the type of tumor, its location, and whether it is benign or malignant, these types of tumors may be slow or fast growing and may or may not metastasize."
Benign tumors typically grow slowly and locally. The growth of malignant tumors can be more rapid and depends on the type of tumor – and even the type of pet. For example, in dogs squamous cell carcinomas do not tend to metastasize, while in cats, they do. Malignant tumors can spread locally, extending into the underlying tissues, or to other areas of the body, including the nearby lymph nodes, lungs, and bone.
Depending on the type of tumor (benign or malignant), staging (searching for potential spread to other locations in the body) is sometimes recommended. This may include radiographs (X-rays) of the lungs, bloodwork, urinalysis, and possibly an abdominal ultrasound. If the lymph nodes appear to be affected, they may be sampled by FNA to determine if spread has occurred.
What are the treatments for these types of tumors?
The treatments for these types of tumors varies with the type of tumor, its location, and its size, and may include surgical removal, radiation therapy, and freezing (cryotherapy). In some cases medical therapy (antibiotics, anti-inflammatories) may be indicated to control pain and clear secondary bacterial infections.
"The treatments for these types of tumors varies with the type of tumor, its location, and its size, and may include surgical removal, radiation therapy, and freezing."
Because these tumors tend to be disfiguring, bothersome, sometimes painful, and may predispose to secondary problems such as eye infections and corneal ulcers, they are usually surgically removed. Prompt removal helps to prevent the secondary problems, and in cases of malignancy, reduce the chance for metastasis. As compared to tumors of the eyelids, tumors of the conjunctiva typically require more extensive surgery to remove them. After surgery, regular rechecks are advisable as conjunctival tumors may regrow.
Radiation therapy may be used in cats with squamous cell carcinoma of the eyelids, particularly when surgery cannot be performed. Radiation therapy has the risk of causing damage to the eye, and in some cases, eye removal (enucleation) may be recommended.
Is there anything else I should know?
The prognosis for tumors of the eyelids, conjunctiva, and periocular tissues depends on the type of cancer, its location, and whether it is benign or malignant. It also depends on how early the tumor is identified and treated. As with all cancers, early intervention offers the best prognosis.