Health

Skin Cancer: What Is It?

Skin Cancer: The Basics

Introduction

Each year, about a million people in the United States learn that they have skin cancer. This National Cancer Institute (NCI) booklet will give you some important information about this disease. It explains how skin cancer is diagnosed and treated and has information about preventing this disease.

Research has led to better methods of diagnosing and treating this disease. It is encouraging to know that skin cancer is now almost 100 percent curable if found early and treated promptly.

Our knowledge about skin cancer and other types of cancer is increasing rapidly. For up-to-date information or to order this publication, call the NCI-supported Cancer Information Service (CIS) toll free at 1-800-4-CANCER (1-800-422-6237). 

The Skin

The skin is the body’s outer covering. It protects us against heat, light, injury, and infection. It regulates body temperature and stores water, fat, and vitamin D. Weighing about 6 pounds, the skin is the body’s largest organ. It is made up of two main layers: the outer epidermis and the inner dermis.

The epidermis (outer layer of the skin) is mostly made up of flat, scale-like cells called squamous cells. Under the squamous cells are round cells called basal cells. The deepest part of the epidermis also contains melanocytes. These cells produce melanin, which gives the skin its color.

The dermis (inner layer of skin) contains blood and lymph vessels, hair follicles, and glands. These glands produce sweat, which helps regulate body temperature, and sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin’s surface through tiny openings called pores.

What Is Cancer?

Cancer is a group of more than 100 diseases. Although each type of cancer differs from the others in many ways, every cancer is a disease of some of the body’s cells.

Healthy cells that make up the body’s tissues grow, divide, and replace themselves in an orderly way. This process keeps the body in good repair. Sometimes, however, normal cells lose their ability to limit and direct their growth. They divide too rapidly and grow without any order. Too much tissue is produced, and tumors begin to form. Tumors can be benign or malignant.

• Benign tumors are not cancer. They do not spread to other parts of the body and are seldom a threat to life. Often, benign tumors can be removed by surgery, and they are not likely to return.

• Malignant tumors are cancer. They can invade and destroy nearby healthy tissues and organs. Cancer cells also can spread, or metastasize, to other parts of the body and form new tumors.