Melanoma Staging Classification: Stage 2A to Lung Metastasis
This melanoma should be reclassified as Stage IV M1b disease, specifically indicating lung metastasis with or without M1a disease. 1
Current Stage Classification
The presence of distant lung metastasis automatically upgrades this melanoma to Stage IV disease, regardless of the initial Stage 2A classification. 1 According to the AJCC 8th edition TNM classification system, the M1b designation specifically applies to lung metastasis with or without M1a (distant skin, soft tissue, or nonregional lymph node) involvement. 1
Key Staging Components to Document
When reporting this Stage IV disease, you must document:
- All sites of metastatic disease (in this case, lung-only metastasis) 1
- Serum LDH level at diagnosis of Stage IV, as this is an independent predictor of poor outcome and incorporated into AJCC staging 1
- Number and location of lung metastases (solitary versus multiple), as this has significant prognostic implications 2
- Presence or absence of extrapulmonary disease, which independently predicts survival 2
Prognostic Implications
The M1b classification (lung-only metastasis) carries a better prognosis than M1c (non-CNS visceral metastases) or M1d (CNS metastases), though still represents advanced disease. 1
Critical prognostic factors that should be assessed include:
- Solitary versus multiple pulmonary metastases: A solitary pulmonary metastasis confers significantly better survival (HR 2.7) compared to multiple lesions 2
- Absence of extrapulmonary disease: This independently predicts improved survival (HR 1.9) 2
- Elevated LDH: This indicates worse prognosis and must be documented 1
Treatment Considerations
For this Stage IV M1b disease, molecular testing for BRAF mutations is mandatory before initiating systemic therapy. 3 Additional testing for NRAS and c-kit mutations should be performed if BRAF is wild-type. 3
Surgical Metastasectomy Consideration
Pulmonary metastasectomy should be considered if the patient has:
- A solitary pulmonary metastasis 2
- Absence of extrapulmonary disease 2
- Good performance status 4
- Long disease-free interval from initial diagnosis 4
Metastasectomy independently predicts survival (HR 0.42) in carefully selected patients, with median survival of 40 months versus 13 months in non-surgical patients. 2 However, 88% of patients experience recurrence at a median of 5 months post-procedure. 2
Systemic Therapy Options
For patients with resected Stage IV disease (if metastasectomy is performed):
- Adjuvant immunotherapy with checkpoint inhibitors can be considered, though prospective data specifically for resected Stage IV disease are limited 1
- Adjuvant dabrafenib plus trametinib can be considered for completely resected BRAF-V600-mutated Stage IV melanoma if there is a contraindication to immunotherapy 1
Common Pitfalls
Do not continue using the Stage 2A designation once distant metastasis is confirmed—this represents a fundamental change in disease classification and prognosis. 1
Do not assume all lung metastases have the same prognosis—the number of lesions and presence of extrapulmonary disease dramatically affect outcomes. 2
Do not proceed with treatment without molecular testing—BRAF mutation status is essential for treatment planning in Stage IV disease. 3