Typical Metastatic Sites for Melanoma
Melanoma most commonly metastasizes to regional lymph nodes first, followed by distant sites including lungs, liver, brain, bone, and small bowel, with virtually any organ potentially affected through predominantly hematogenous spread. 1, 2
Pattern of Metastatic Spread
Regional Metastases
- Lymph nodes are the initial and most common site of metastatic spread, with risk directly correlated to primary tumor thickness and level of invasion 1
- Regional nodal involvement occurs in 5-40% of patients depending on primary tumor characteristics 1
- In-transit metastases (between primary site and regional nodes) represent another pattern of locoregional spread 1
Distant Metastatic Sites (Stage IV)
Most Common Visceral Sites:
- Lungs - among the most frequently involved organs 1, 2, 3, 4
- Liver - commonly affected and associated with poor prognosis 1, 2, 5, 3, 4
- Brain - frequent site of metastasis, particularly in patients with initially localized lesions 1, 4
- Bone - common metastatic site 4, 6
- Small bowel - frequently involved gastrointestinal site 2, 3
Additional Sites:
- Virtually any organ can be affected by melanoma metastases 2, 6
- Skin and subcutaneous tissues (distant from primary) 5
- Other lymph node basins beyond regional drainage 6
Clinical Implications by Site
Prognostic Significance
- Liver and brain metastases are associated with shorter overall survival compared to lung, lymph node, or subcutaneous metastases 1, 5
- The site of metastasis is the most significant predictor of outcome in stage IV disease 1
- Elevated lactate dehydrogenase (LDH) is an independent poor prognostic indicator and should be measured at stage IV diagnosis 1
Imaging Recommendations for Detection
- Abdominal, thoracic, and cerebral CT scans are the most useful imaging modalities for detecting distant metastases 1
- Brain imaging (MRI or CT with contrast) should be performed even with minimal CNS symptoms, as cerebral metastases may be present with few other metastatic sites 1, 4
- In approximately 10% of cases, distant asymptomatic metastases are discovered at the time of regional nodal involvement diagnosis 1
Unique Characteristics
- Melanoma metastases spread predominantly through hematogenous routes, distinguishing it from many other solid tumors 2, 6
- Liver and brain metastases demonstrate significantly reduced immune infiltration compared to lung, subcutaneous, and lymph node metastases, potentially explaining poorer immunotherapy response rates 5
- Melanoma can produce unpredictable manifestations that may be indistinguishable from other diseases on imaging alone 2