Clark’s level

December 20, 2023

Clark’s level is a system used in pathology reports to describe how far a skin cancer such as invasive squamous cell carcinoma or invasive melanoma has spread into the skin. It’s an important factor in determining the severity and potential behaviour of the tumour. The system consists of five levels, each indicating how deeply the tumour has penetrated through the layers of the skin:

1. Level I: The tumour is confined to the epidermis, the outermost layer of skin. Depending on the tumour type, this is also known as squamous cell carcinoma in situ or melanoma in situ.
2. Level II: The tumour has penetrated the papillary dermis, the upper part of the second layer of skin.
3. Level III: The tumour has filled the entire papillary dermis but has not reached the reticular dermis, the lower part of the second layer of skin.
4. Level IV: The tumour has invaded the reticular dermis.
5. Level V: The tumour has penetrated the subcutaneous fat, the layer beneath the skin.

Each increase in Clark’s level indicates a deeper penetration of the tumour and potentially a worse prognosis, as deeper tumours have a higher risk of metastasizing (spreading) to lymph nodes. However, it’s important to note that while Clark’s level provides valuable information about the depth of the tumour, other factors like the tumour thickness (which measures the actual depth of the invasion in millimetres) and the presence of ulceration are also critical for staging and prognosis. The combined assessment of these factors helps guide treatment decisions.

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