Sentinel lymph node mapping: A diagnostic procedure used to determine the first lymph node or nodes that drain a tumor for removal and examination for possible lymph node involvement. If the sentinel node is cancer-free, then other lymph nodes are also considered cancer-free.

Sentinel node: The first lymph node or nodes to drain a tumor. The sentinel node is located and removed in a procedure called sentinel lymph node mapping to determine whether the cancer has spread to the lymph nodes.

Side effect: A result of drug or other therapy which is in addition to the desired therapeutic effect.

Site: The part of the body where a cancer first appears.

Skin graft: A surgical procedure in which a piece of skin is transplanted from one area to another.

Skin: The outer covering of the body, consisting of an outer layer, the epidermis, an inner layer, the dermis, and a layer of fatty tissue.

Skin lesion: Changes in color or texture of the skin.

SLN biopsy: A surgical procedure in which lymph nodes that drain a tumor are identified and examined under a microscope to check for cancer cells.

SPF: See Sun protection factor.

Squamous cell carcinoma: Cancer of the squamous cell.

Squamous cells: Flat cells that make up most of the epidermis, the outer layer of skin; they look like fish scales.

Stage: The extent of a cancer, especially whether the disease has spread from the original site to other parts of the body.

Staging: A system for determining how far a tumor has spread from its point of origin.

Stress: A reaction of the body to a perceived or imagined threat.

Subcutaneous: Under the skin.

Subcutis: The deepest layer of skin. Together with the lower part of the dermis, the subcutis contains fatty tissue and collagen. The subcutis conserves heat and helps protect the body's organs from injury.

Sun protection factor (SPF): A scale for rating sunscreens. Sunscreens with an SPF of 15 or higher provide the best protection from the sun's harmful rays.

Sunscreen: A substance that helps to block the effect of the sun's harmful rays. Using lotions or creams that contain sunscreens can help protect the skin from premature skin aging and damage that may lead to cancer.

Surgical excision: Removal of tissue by a doctor or surgeon using a scalpel (sharp knife) or other instrument designed for cutting.

Systemic treatment: Treatment using substances that travel through the bloodstream, reaching and affecting cancer cells all over the body.