The short answer
Clark level is a scale from I to V that names the deepest skin layer a melanoma reaches. Level I stays in the top layer. Level V reaches the fat under the skin. NCI notes that Breslow thickness is more reproducible, so current staging relies on thickness. This page explains both.
Clark level names the deepest layer of skin the melanoma reaches, on a scale from I to V.
It is a description of layers, not a measurement in millimeters.
NCI states that Breslow thickness is more reproducible and should always be reported. Current T categories use thickness.
If your report lists a Clark level, ask your care team how it fits with the rest of your report.
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This page is for anyone whose melanoma pathology report lists a Clark level. It explains what each level means and how it relates to Breslow depth.
Clark level describes skin layers
Skin has layers. The top layer is the epidermis. Under it is the dermis, which has a thin upper part (papillary dermis) and a thicker lower part (reticular dermis). Under that is a layer of fat called subcutaneous tissue.
Clark level names the deepest layer the melanoma reaches. NCI lists five levels:
- Level I: only in the epidermis. This is melanoma in situ. It is not invasive.
- Level II: grows into the papillary dermis.
- Level III: fills and expands the papillary dermis, but does not go into the reticular dermis.
- Level IV: grows into the reticular dermis, but not into the fat below.
- Level V: grows through the dermis into the subcutaneous tissue.
How Clark level compares with Breslow depth
Breslow depth is a measurement in millimeters. Clark level is a description of layers. Skin is thicker in some parts of the body than others, so the same Clark level can mean a different real depth.
NCI states that Breslow thickness "is more reproducible" and "should always be reported." Current T categories for melanoma are based on thickness and on whether the tumor is ulcerated. That is why many newer reports focus on Breslow depth, and some leave Clark level out.
If your report lists both, the Breslow depth is the one that sets the T category. See What Does Breslow Depth Mean?
What Clark level does not tell you
Clark level is about the main tumor only. It does not say whether cancer is in lymph nodes or elsewhere. It is not a stage.
It also does not predict what will happen to you. Your care team looks at the full report, including thickness, ulceration, and lymph node results, to plan next steps.
Ask these before you leave
- What Clark level and Breslow depth are on my report?
- Which one is used for my T category?
- Is the tumor ulcerated?
- What are the next steps, and why?
Related pages
See Melanoma Stages, What Does Carcinoma In Situ Mean?, and Understanding Your Pathology Report.
Sources
Common questions
What is Clark level?
It is a scale from I to V that describes how deep into the layers of the skin a melanoma has grown. Level I is only in the top layer. Level V has reached the fat under the skin.
Is Clark level still used?
Some reports still list it. NCI notes that Breslow thickness is more reproducible and should always be reported, and current T categories are based on thickness and ulceration.
Is Clark level the same as stage?
No. Stage combines the main tumor, lymph nodes, and any distant spread. Clark level describes only the depth of the main tumor by skin layer.
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
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