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Acral: In reference to the skin, acral refers to the palms of the hands or the soles of the feet.
Actinic: Developing due to exposure to the sun.
Amelanotic: Does not contain the pigment melanin.
Basal cell: The cell type located in the deepest layer of the epidermis, which is responsible for creating new skin cells. When basal cells become cancerous, they form a basal cell carcinoma.
Benign: Not cancerous.
Biopsy: A medical procedure in which a small piece of skin or tissue is removed and is then examined under a microscope by a pathologist (medical doctor/MD with specialized training in pathology) to determine a diagnosis.
Cancer: The uncontrolled proliferation of abnormal cells. Cancerous cells differ from non-cancerous cells in that they have the potential to spread to other parts of the body and cause disease in distant organs and structures.
Carcinoma: A cancer of epithelial cells. Epithelial tissues line nearly all surfaces and cavities of the body, including the skin, other organs, and blood vessels.
Carcinoma in-situ: A cancerous tumor of the epithelial cells that has not left its location of origin. In other words, the cancer has not spread to near or distant structures.
Congenital: Describing a condition that has been present since birth.
Crust: In the context of the skin, a dry and hardened layer overlying a lesion or wound, commonly called a scab.
Dermatologist: A physician (medical doctor/MD) who has specialized training in diagnosing skin cancers and diseases of the skin, hair or nails.
Dermis: The layer of skin that is sandwiched between the epidermis and hypodermis. The dermis contains connective tissue, hair follicles, sweat glands, blood vessels, nerves, and immune cells.
Epidermis: The most superficial (outer) layer of cells in the skin. Cell types that are found within the epidermis include basal cells, squamous cells (keratinocytes), melanocytes and Merkel cells.
Hyperplasia: An increase in the number of cells of an organ or tissue, causing the organ or tissue to become enlarged. This can be an initial step in the development of cancer.
Hypodermis: The tissue layer that is located below the dermis. The hypodermis connects the skin to the fibrous tissue of the bones and muscles and is used for fat storage. The hypodermis is also called the subcutaneous layer or superficial fascia.
Incidence: The number of cases of a medical condition occurring in a population within a specific period of time. This can also refer to the number of cases per unit of people; for instance, the number of cases of a disease each year per 100,000 people in a specific population.
Invasive cancer: When cancer cells have broken out of the tissue they began in and have spread to nearby tissue or to distant organs.
Keratin: A protein that is responsible for the structure of hair, nails, and the outer layer of skin. In skin, keratin protects the cells from damage and stress.
Keratinocyte: A cell type that is found in the outer layer (epidermis) of the skin and produces keratin. Keratinocytes protect against pathogens and ultraviolet (UV) radiation and minimize heat and water loss. In the skin, keratinocytes are also referred to as squamous cells. When keratinocytes in the skin become cancerous, they form a squamous cell carcinoma.
Keratosis: A growth on the skin, such as a wart or callus, that is made primarily from keratin. A keratotic skin growth tends to feel rough or scaly, rather than soft like normal skin.
Lesion: An area of an organ or tissue that has been injured or damaged or contains abnormal cells, such as a wound or a tumor.
Lynch syndrome: An inherited condition that increases the risk of many types of cancer, including cancer of the colon, skin, and endometrium. Lynch syndrome was formerly called hereditary nonpolyposis colorectal cancer (HNPCC).
Melanin: A dark brown or black pigment that is found in the hair, skin, and eyes. Melanin is responsible for the darkening of skin when exposed to sunlight.
Malignant: Describes a disease (e.g., cancer) where the cells are abnormal and grow uncontrollably. These cells can spread to nearby tissues and to other areas of the body.
Melanocytes: Cells that produce the pigment melanin, which gives eyes, skin, and hair its color. Melanocytes that become cancerous form a tumor called a melanoma.
Margin: Edge or border. When a skin cancer is surgically removed, the tissue is examined under a microscope by a pathologist to determine if the margins appear to be free of cancer cells. If cancer cells are observed at the edges of the tumor, the margins are said to be positive, which suggests that the tumor may not have been completely removed.
Merkel cells: A cell type that is found at the base of the skin epidermis, nestled between basal cells. The exact function of Merkel cells remains unclear. When Merkel cells become cancerous, they form a neuroendocrine tumor called Merkel cell carcinoma.
Metastasis/metastasize: When cancer spreads from where it first formed. For example, a melanoma of the forearm that has metastasized to the brain. This patient now has metastatic melanoma, not a new primary brain cancer.
Mucosa: Cell layer that lines the internal organs and surfaces within the body. Mucosa cells produce mucus, causing mucosal surfaces, such as the inside of the mouth, to feel wet or slippery.
Mutation: Change in the structure of DNA. Many mutations are harmless, but others can lead to the development of cancer.
Neoplasm: A tumor, or unusual growth that grows faster than normal. Although neoplasms can be either benign (non-cancerous like a wart) or cancerous, today the term is more often used to refer to a malignant growth.
Neoplastic: Related to a neoplasm or tumor.
Neuroendocrine: Relationship between the nervous system (brain and nerves) and endocrine system (makes hormones). Neuroendocrine tumors are rare and contain cells that have features of both nerve cells and endocrine cells Merkel cell carcinoma is an example of a neuroendocrine tumor that occurs in the skin.
Nevus/nevi: Medical term for a mole(s).
Nodule: Lumps that grow under the skin.
Pathologist: A physician (medical doctor/MD) who is trained to diagnose diseases by examining tissue under the microscope and by conducting specialized laboratory tests on tissue samples.
Pigment: Gives color to eyes, hair, and skin.
Sebaceous: Pertaining to the oil-secreting sebaceous glands of the skin.
Sebum: The oily, yellowish substance secreted by the sebaceous glands to lubricate the skin and protect it from drying out.
Solar: Caused or produced by the sun.
Squamous cell: Flat, thin cells that line external and internal surfaces of the body. Squamous cells in the epidermis of the skin are also called keratinocytes because of their production of keratin. Squamous cells in both skin and internal organs can give rise to squamous cell carcinoma, but these cancers behave differently.
Subungual: Located under the nail of a toe or finger. For example, a subungual melanoma that develops under a fingernail.
Symptomatic: The state of being in which one experiences and/or displays the effects of a disease. A growth in the skin that is symptomatic might be itchy, sore or bleed.
Translucent: Semi-clear; images seen through translucent materials look out of focus or like shadows. For example, some basal cell carcinomas appear to be almost translucent.
Tumor: A mass or growth made up of cells that divide more rapidly than normal. Tumors may be benign, pre-malignant, or malignant.
Ulcerated: Having developed an ulcer (or ulcers). Ulcerated skin tumors may bleed, ooze, or have scabs on their surface.
Ultraviolet light (UV): A kind of radiation that has more energy than visible light but less energy than X-rays. We can’t see it, but it is still damaging to our eyes, skin, and DNA. UV radiation is naturally emitted from the sun but can also be produced artificially by devices like sunlamps used in tanning parlors.