Q. How does basal cell carcinoma differ from other skin cancers and how is it treated?

A. Basal cell carcinoma is the most common skin cancer: The American Cancer Society estimates that 8 out of 10 skin cancers are basal cell carcinomas. It is the major reason that more people develop skin cancer than all other forms of cancer combined.

All skin cancers involve cells with abnormal genetic changes that allow them to multiply uncontrollably and form tumors, but their severity and effects differ depending on the types of cells they originate from, how fast they grow, and whether they spread to other tissues. Skin cancers are usually grouped into two major categories: melanoma and nonmelanoma. Melanoma is a cancer of skin cells that produce the pigment melanin; it is the most dangerous form of skin cancer because it’s more likely to spread to other parts of the body. Over 99 percent of nonmelanoma skin cancers are either basal cell carcinoma or squamous cell carcinoma. Both arise from cells called keratinocytes that are the main structural component of the skin.

Basal cell carcinoma is a slow-growing cancer that very rarely metastasizes and is considered the least dangerous skin cancer. But Dr. Thomas Kupper, chief of dermatology at Brigham and Women’s Hospital and Dana-Farber Cancer Institute, emphasizes that squamous and basal cell carcinomas can invade adjacent tissues, including bone, and can cause damage if not caught early.