Cancer begins when healthy cells change and grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Eyelid cancer is a general term for a cancer that occurs on or in the eyelid. It is broadly categorized as an epithelial tumor, which is on the outer surface. An eyelid tumor can begin from sebaceous (fat), sweat, or apocrine glands, which is a type of sweat gland.
The most common types of cancer occurring on the eyelid are:
Basal cell carcinoma. Under the squamous cells (flat, scale-like cells) in the lower epidermis are round cells known as basal cells. About 80% of skin cancers arise from this layer in skin, and they are directly related to exposure to the sun. Basal cell carcinoma is the most common type of eyelid cancer. It usually appears in the lower lid and occurs most often in individuals with fair or pale skin.
Sebaceous carcinoma. Mostly occurring in middle age to older adults, sebaceous carcinoma is the second most common eyelid cancer. It may start from meibomian glands, which are glands of the eyelids that discharge a fatty secretion that lubricates the eyelids. Less frequently, it starts from glands of Zeis, the sebaceous glands at the base of the eyelashes. Sebaceous carcinoma is an aggressive cancer that normally occurs on the upper eyelid and is associated with radiation exposure, Bowen’s disease, and Muir-Torre syndrome. A large sebaceous carcinoma or one that returns after treatment may require surgical removal of the eye.
Squamous cell carcinoma. Squamous cells make up most of the top layer of the epidermis. Approximately 10% to 30% of skin cancers begin in this layer. These skin cancers usually arise from sun exposure. They may also appear on skin that has been burned, damaged by chemicals, or exposed to x-rays. Squamous cell carcinoma is much less common than basal cell carcinoma, but it behaves more aggressively and can more easily spread to nearby tissues.
Melanoma. The deepest layer of the epidermis contains scattered cells called melanocytes, which produce the melanin that gives skin color. Melanoma starts in melanocytes, and it is the most serious of the three skin cancer types.
The rest of this guide focuses on skin cancer, particularly melanoma.