Staging of malignant melanoma

Staging of primary melanoma can be carried out in 2 steps

• initial staging is based on the histopathological features reported by the pathologist looking at the microscopic sections of the tumour
  • melanoma is staged as 0-IIC, based on factors such as the thickness of the tumour and the presence or absence of ulceration
• in many hospitals in the UK, this first step is followed by the option of a second, which is a sampling of the lymph nodes most likely to contain secondary melanoma cells (sentinel lymph node biopsy). If a sentinel lymph node biopsy is performed and microscopic disease is detected, the melanoma becomes stage III. If no microscopic disease is detected then the initial stage is used

Summary of the TNM staging used for melanoma is below:

Primary Tumour (T)

• TX Primary tumor cannot be assessed (for example, curettaged or severely regressed melanoma)
• T0 No evidence of primary tumor
• Tis Melanoma in situ
• T1 Melanomas 1.0 mm or less in thickness
• T2 Melanomas 1.01-2.0 mm
• T3 Melanomas 2.01-4.0 mm
• T4 Melanomas more than 4.0 mm

NOTE: NICE guidance states a and b subcategories of T are assigned based on ulceration and number of mitoses per mm2, as shown below (1)

Note that the AJCC 8th Edition of melanoma staging has changed the classification of T1a and T1b melanoma (and have removed the number of mitoses per mm2 as part of the classification) (2)

• T1a: < 0.8 mm thickness without ulceration
• T1b: < 0.8 mm thickness with ulceration or 0.8 - 1.0 mm thickness with or without ulceration

Regional Lymph Nodes (N)

• NX Patients in whom the regional nodes cannot be assessed (for example, previously removed for another reason)
• N0 No regional metastases detected
• N1-3 Regional metastases based upon the number of metastatic nodes and presence or absence of intralymphatic metastases (in transit or satellite metastases)

NOTE: N1-3 and a-c subcategories assigned as shown below

Notes

• 1 Micrometastases are diagnosed after sentinel lymph node biopsy and completion lymphadenectomy (if performed)
• 2 Macrometastases are defined as clinically detectable nodal metastases confirmed by therapeutic lymphadenectomy or when nodal metastasis exhibits gross extracapsular extension

Distant Metastatis (M)

• M0 No detectable evidence of distant metastases
• M1a Metastases to skin, subcutaneous, or distant lymph nodes
• M1b Metastases to lung
• M1c Metastases to all other visceral sites or distant metastases to any site combined with an elevated serum LDH

NOTE: Serum LDH is incorporated into the M category as shown below:

Clinical staging includes microstaging of the primary melanoma and clinical/radiologic evaluation for metastases

• should be used after complete excision of the primary melanoma with clinical assessment for regional and distant metastases

Reference:

• NICE (July 2015).Melanoma: assessment and management
• AJCC, 8th Edition, 2018