Melanoma: Diagnosis - TNM

The pathologist will report on different aspects of the melanoma:

T stands for thickness. This is based on an important measurement for how thick (deep) a melanoma is, called Breslow thickness. It is the distance in millimetres from the surface of the skin to the deepest melanoma cells. The different depths are:

• Less than or equal to 0.75 mm

• 0.76-1.5 mm

• 1.51-4 mm

• Greater than or equal to 4 mm

It also looks at whether the melanoma is ulcerated. A melanoma is said to be ulcerated if the layer of skin covering the melanoma cannot be clearly seen.

N refers to whether the melanoma has spread to the lymph nodes.

M is whether the melanoma has spread to other parts of the body (secondary or metastatic cancer). 

There are also different levels of how far the tumour extends that is used in conjunction with Breslow thickness called Clark’s Level:

• Level I – Melanoma confined to the epidermis (melanoma in situ)

• Level II – Tumour extends into the papillary dermis

• Level III – Tumour extends to in between the papillary and reticular dermis

• Level IV – Tumour extends into the reticular dermis

• Level V – Tumour invasion of subcutaneous tissue