Clark levels in melanoma: meaning and Breslow comparison

The five anatomical levels

1. I: confined to the epidermis; melanoma in situ.
2. II: invasion into the papillary dermis.
3. III: fills the papillary dermis to its interface with the reticular dermis.
4. IV: invasion into the reticular dermis.
5. V: invasion into subcutaneous tissue.

Clark, Breslow and TNM are different concepts

Clark describes which layer is involved; Breslow measures thickness in millimetres; TNM also describes regional and distant spread. A Clark level cannot be converted directly into a TNM stage.

Reading an older report

Clark level may appear in older reports. Ask your doctor to interpret it alongside Breslow thickness, ulceration and stage. Older diagrams displaying survival percentages have been removed from this page to avoid misleading comparisons.

Clark level III or IV is not stage III or IV melanoma

A Roman numeral in a pathology report can cause understandable confusion. Clark level IV means invasion into the reticular dermis, a layer of the skin. It does not mean stage IV melanoma. Likewise, Clark level III describes the depth of invasion within the skin, not lymph-node involvement.

The overall TNM stage answers a different question: how extensive is the disease? A Clark level alone cannot establish that stage or select a treatment.

Why is Breslow thickness used instead?

Breslow thickness measures vertical depth in millimetres. Clark assessment depends on identifying anatomical boundaries and is less reproducible. Clark level is no longer used in the AJCC eighth-edition staging criteria, although a pathology report may still mention it.

Questions to take to your appointment

• Does this number refer to a Clark level or to the overall melanoma stage?
• What are the Breslow thickness and ulceration findings?
• Is staging complete, or are any additional assessments needed?
• Which findings determine the next step in my care?

These distinctions help you read the report accurately; they cannot provide an individual prognosis without the remaining clinical information.