Cancer Skin Cancer Diagnosis Breslow Thickness of a Melanoma This tumor classification help determine one's prognosis By Timothy DiChiara, PhD Timothy DiChiara, PhD Timothy J. DiChiara, PhD, is a former research scientist and published writer specializing in oncology. Learn about our editorial process Updated on March 23, 2022 Medically reviewed by Doru Paul, MD Medically reviewed by Doru Paul, MD Doru Paul, MD, is triple board-certified in medical oncology, hematology, and internal medicine. He is an associate professor of clinical medicine at Weill Cornell Medical College and attending physician in the Department of Hematology and Oncology at the New York Presbyterian Weill Cornell Medical Center. Learn about our Medical Expert Board Print If your healthcare provider sees a suspicious mole during an exam, the next step is a skin biopsy. If that reveals melanoma, a pathologist will perform tests to determine how advanced the disease is—a process called staging. In addition, the thickness of the tumor is measured and assigned what's called a Breslow number. This figure has been found to be significant when coming up with a patient's prognosis. damiangretka/Getty images Once the stage and the Breslow number have been accurately determined, your healthcare provider can effectively plan your treatment. The TNM System In 2016, the American Joint Committee on Cancer (AJCC) released new guidelines for staging melanoma, known as the TNM system. Each letter of this name stands for a different aspect of a tumor's characteristics: T (tumor): The important aspects of the tumor itself include how big it is, whether it has ulcerated (there is a breakdown of the skin over the melanoma), and if it has spread beyond its own boundaries.N (lymph nodes): Has the cancer spread to nearby lymph nodes?M (metastasis): Has the cancer spread to distant lymph nodes or distant organs, such as the lungs, liver, brain, or bones? Once TNM factors have been identified, the cancer is given a number from 0 to IV— and sometimes a letter, from A to C—with higher numbers meaning the cancer is more advanced. Melanoma Stages 0 Through IV Breslow Thickness Besides the TNM number, you may also hear the healthcare provider refer to a Breslow number, a measurement of thickness used for melanomas that have not spread. (Another measurement, called the Clark level, is no longer used as it has been deemed too subjective.) In general, melanomas less than 1 millimeter (mm) thick—about 1/25 of an inch—have a very small chance of spreading. As the melanoma becomes thicker, it has a greater chance of spreading. First reported by Alexander Breslow, MD, in 1970, the Breslow thickness is defined as the total vertical height of the melanoma, from the very top (called the granular layer) to the area of deepest penetration in the skin. An instrument called an ocular micrometer is used to measure the thickness of the excised (removed) tumor. Due to its accuracy in predicting outcomes, the Breslow thickness has been incorporated into the standard TNM staging system for melanoma. The Breslow thickness is an extremely important prognostic factor in melanoma, along with tumor (T) stage and the existence of skin ulceration (broken skin, bleeding, swelling). In general, the higher the Breslow thickness, the worse the prognosis—in other words, the thicker the melanoma, the greater chance it has of spreading. Prognosis Based on Breslow Number Five-year survival rates can be determined by Breslow thickness. Keep in mind that these survival rates are averages and may not reflect your individual case: Less than 1 mm: Around 95%, meaning 95 people out of 100 people will be alive five years after being diagnosed with a melanoma that is less than 1 mm thick1.01 to 2 mm: Around 90%2.01 to 4 mm: Around 77%Greater than 4 mm: 65% A Word From Verywell While melanoma can be a frightening diagnosis, more and more effective treatments are available, even for late-stage cancers. Accurate staging will result in receiving the most effective treatment possible. Skin Cancer Doctor Discussion Guide Get our printable guide for your next doctor's appointment to help you ask the right questions. Download PDF Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. 3 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. National Cancer Institute. SEER Training Modules. Melanoma staging schemes. Melanoma Molecular Map Project. TNM staging. Gawkrodger, D, Ardern-Jones, MR. Dermatology E-Book: An Illustrated Colour Text. New York, NY: Elsevier Health Science; 2016. Additional Reading American Cancer Society. Melanoma skin cancer stages. American Cancer Society. Survival rates for melanoma skin cancer, by stage. Balch CM, Gershenwald JE, Soong SJ, et al. Final version of 2009 AJCC melanoma staging and classification. J Clin Oncol. 2009;27(36):6199-206. doi:10.1200/JCO.2009.23.4799 Gershenwald, JE, AJCC Melanoma Staging System (8th Edition) By Timothy DiChiara, PhD Timothy J. 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