What is the difference between satellite lesions and melanoma in transit in a patient with a history of melanoma, particularly nodular or desmoplastic subtypes?

Satellite Lesions vs Melanoma In-Transit: Key Distinctions

Satellite lesions are lymphatic metastases located within or immediately adjacent to the primary melanoma biopsy site or wide excision scar, while in-transit metastases are lymphatic deposits located between the primary tumor and the regional lymph node basin. 1

Anatomic Location Defines the Distinction

The critical differentiating factor is anatomic proximity to the primary site:

• Satellite metastases: Occur within or directly adjacent to the melanoma biopsy site or subsequent wide excision scar 1
• In-transit metastases: Located between the primary tumor site and the regional lymph node basin, but not reaching the nodal basin 1, 2

Both represent lymphatic spread of melanoma cells through dermal and subcutaneous lymphatic channels rather than hematogenous dissemination 2

Microscopic vs Macroscopic Presentation

Microsatellites (Microsatellitosis)

• Detected histopathologically in either the biopsy or wide excision specimen 1
• Not clinically apparent but identified on pathologic examination 1
• Must be documented in pathology reports on biopsy or wide excision specimens 1

Macroscopic Satellites

• Clinically apparent satellite lesions visible on examination 1
• Should be documented on gross tumor specimens 1

Staging Implications: All Confer Stage III Disease

Both satellite and in-transit metastases upstage patients to Stage III melanoma, regardless of whether regional nodal disease is present. 1

AJCC-8 N Classification

• Results in N classification of N1c, N2c, or N3c based on the number of tumor-involved regional lymph nodes (0,1, or ≥2 respectively) 1
• Microsatellites alone (without regional nodal disease) classify as at least N1c 1
• If sentinel lymph node biopsy is positive in a patient with microsatellites, this upstages to at least N2c, Stage IIIC 1

Prognostic Significance

Survival outcomes are similar among patients with microsatellites, macroscopic satellites, and in-transit metastases, with all three conferring worse survival compared to melanoma without these features. 1

Key Prognostic Points

• All three patterns are associated with poorer relapse-free survival (RFS), disease-specific survival (DSS), and overall survival (OS), even among patients with synchronous nodal disease 1
• Microsatellites are linked to higher rates of sentinel lymph node positivity 1
• Some studies suggest patients with Stage III melanoma based on microsatellitosis alone may have higher melanoma-specific survival rates compared to those with satellite/in-transit metastasis or positive sentinel lymph node biopsy, though this remains debated 1
• Patients presenting with satellite or in-transit metastases at initial diagnosis have worse outcomes, suggesting more aggressive disease biology 3

Management Differences

NCCN Guidelines recommendations differ based on the type of regional disease present:

For Microsatellites (ME-4 pathway)

• Sentinel lymph node biopsy should be considered, especially if it will alter management decisions 1
• Adjuvant treatment considerations differ from those with nodal or clinical satellite/in-transit disease 1
• Patients with microsatellitosis alone were not included in prospective randomized trials testing adjuvant therapy for resected Stage III melanoma 1

For Clinical Satellites or In-Transit Disease (ME-7 pathway)

• Management differs from patients without regional disease (ME-1 and ME-2) or those with regional disease limited to lymph nodes (ME-5 and ME-6) 1
• Definitive surgical resection remains the preferred therapeutic approach when feasible 2
• When surgery cannot achieve reasonable cosmetic and functional outcomes, local, regional, or systemic therapies must be considered 2

Critical Pathology Reporting Requirements

Evidence of microsatellites, clinical satellites, and in-transit metastases is a critical element of initial workup and must be included in pathology reports. 1

• Document any macroscopic satellites on gross tumor specimens 1
• Report microsatellites identified histopathologically in biopsy or wide excision specimens 1
• This documentation directly impacts staging, prognosis, and treatment algorithms 1

Special Considerations for Specific Melanoma Subtypes

Desmoplastic Melanoma

• Pure desmoplastic melanoma (>90% of invasive melanoma with prominent stromal fibrosis) has lower rates of sentinel lymph node positivity compared to conventional melanoma 1
• Neurotropism (perineural invasion) increases risk for local recurrence in pure desmoplastic melanoma 1
• Extensive neurotropism, head/neck location, and close histologic margins are risk factors where adjuvant radiation may be considered 1
• The role of sentinel lymph node biopsy in pure desmoplastic melanoma remains controversial due to conflicting reports 1

Nodular Melanoma

• No specific differences in satellite vs in-transit definitions apply to nodular subtype 1
• Standard anatomic location criteria remain the distinguishing feature 1