The depth of tumor invasion is closely related to the patient’s prognosis. Clinically, there are mainly the TNM grading method which was proposed internationally in 1992 after the synthesis of Clark’s grading method and Breslow’s measurement method and American JC (American JC).
1. Clark’s grading method: This method was designed by pathologist Clark to measure the depth of melanoma infiltrating the skin according to the anatomical level. Grade I: Tumor cells are confined to the epidermis above the basement membrane.
Grade II: The tumor cells break through the basement membrane and invade into the dermal papillae.
Grade III: The tumor cells filled the dermal papillary layer and invaded further down, but not to the dermal reticular layer.
Grade IV: The tumor cells have invaded into the dermal reticular layer.
Grade V: The tumor cells have crossed the dermal reticular layer and invaded into the subcutaneous fat layer.
Clark grading provides a grading system for the degree of skin invasion by malignant melanoma, which can evaluate the 5-year survival rate of patients after surgery.
2. Breslow thickness grading: Breslow (1970) studied the relationship between vertical thickness of melanoma and prognosis and classified melanoma into 5 grades based on the thickest part of the melanoma (thickness from the granular layer to the deepest part of the melanoma) measured by an eyepiece micrometer.
Less than 0.75MM, 0.76-1.50MM, 1.51-3.00MM, 3.01-4.50MM and greater than 4.50MM.It was found that the greater the thickness the worse the prognosis. This microscopic grading method, which was widely adopted later, was proved to be of great value in determining prognosis.
3. The American JC proposed the international TNM grading method with the following grading conditions.
1.Primary tumor (PT)
PTx primary tumor cannot be determined.
PT0 No evidence of primary tumor.
PTis primary melanoma (Clark grade I).
PT1 tumor thickness ≤0.75mm, invading the dermal papilla (Clark grade II).
PT2 tumor thickness >0.75mm, <1.5mm, invading the interface between dermal papillae and reticular layer (Clark grade III), or both.
PT3 tumor thickness >0.15mm, <4mm, invading the dermal reticular layer (Clark grade IV), or both.
PT3a tumor thickness >1.5 mm, <3 mm.
PT3b tumor thickness >3mm, <4mm.
PT4 tumor thickness >4mm, invasion of subcutaneous tissue (Clark grade V), or both, or satellite damage within 2cm of the primary tumor.
PT4a tumor thickness >4mm, invading subcutaneous tissues.
PT4b satellite damage within 2cm of the primary tumor.
2.Local lymph nodes (regionallymphnodes, N)
Nx whether local lymph nodes metastasis cannot be determined.
N0No local lymph node metastasis.
N1 local lymph node metastasis, the largest lymph node ≤ 3cm.
N2 local lymph node metastasis with its largest lymph node >3cm.
N2a local lymph node metastasis with its largest lymph node >3cm, or in the process of metastasis.
N3b is in the process of metastasis.
N3c has both N2a and N2b.
3. Distant metastases (distant metastases, M)
Mx distant metastases are uncertain.
M0 no distant metastases.
M1 distant metastases.
M1a metastasis to lymph nodes other than skin, subcutaneous tissue or local lymph nodes.
M1b visceral metastasis.
4.Grading criteria
Grade I PT1 or PT2, N0, M0.
Grade II PT3, N0, M0.
Grade III PT4, N0, M0.
Any PT, N1 or N2, M0.
Grade IV any PT, any N, M1.