Basal Cell Carcinoma is the most common malignant tumor of the skin as well as of the eyelids. It is a low-grade tumor that may be locally invasive but it rarely metastasizes. The risk factors include excessive sun exposure, fair skin, exposure to radiation, history of previous basal cell carcinoma. It begins as a small pimple with a pearly rim and eventually ulcerates with raised edges looking like a crater which is why it's also known as "RODENT ULCER". The more common site of involvement includes the lower eyelid and the tumor is painless. However, it needs treatment otherwise there is a chance that it may metastasize. For tumors that are detected early, surgical excision can be easily done but tumors that are more extensive require special techniques for removal like the Mohs micrographic surgical excision procedure. Radiotherapy and cryotherapy are also useful for treatment but then in these cases there is a higher chance of recurrence.
I had one last year, was in hospital to have it checked ready for removal at a later date. Weirdly it fell off in the shower