Chapter 17: Radiation Therapy for Metastatic Melanoma

RADIATION THERAPY IN PATIENTS WITH AJCC STAGE III MELANOMA

Radiation therapy (RT) in patients with metastatic melanoma in regional lymph nodes may be used as adjuvant treatment, or occasionally as definitive treatment, when surgery is not feasible or contraindicated. The rationale for adjuvant RT in patients with stage III melanoma is to reduce the risk of regional node field recurrence, which can cause significant morbidity and seriously reduce quality of life. The notion that melanoma rarely responds to RT has been dispelled by a recent randomized study in patients with AJCC stage III melanoma that demonstrated a significant reduction in node field recurrence with the addition of adjuvant RT.¹ Whether improved regional control improves survival remains speculative. However, metastasis to a regional node field undoubtedly indicates an increased risk of distant metastasis, with a progressive reduction in survival associated with increasing tumor burden in the node field.²

Node Field Recurrence Following Therapeutic Node Dissection

Multiple surgical series have reported a range of node field recurrence rates, which vary considerably according to the extent of lymph node involvement. Node field recurrences range from 15% to 60%, with a median of approximately 30% (Table 17-1). As expected, locoregional relapse rates tend to increase with worsening histopathologic features. The most important prognostic factor appears to be the presence of extranodal tumor extension, including matted nodes. In a randomized study, extranodal extension was associated with a hazard ratio of 1.69 for node field recurrence after adjusting for other known prognostic factors.³ The number of positive nodes and size of involved nodes are also important; recurrence rates of 60% to 80% have been reported for multiple nodes or nodes >6-cm diameter.⁴ The site of the node field is also relevant, with higher relapse rates in the neck (35% to 45%) compared with the axilla (25% to 35%) and the groin (10% to 20%).⁴

Results of Adjuvant Radiation Therapy After Nodal Dissection

To reduce these high rates of node field relapse, adjuvant RT has been recommended when adverse pathological features have been identified. An earlier phase III trial comparing lymph node dissection alone versus lymph node dissection plus adjuvant RT reported a trend toward improved survival in the RT arm, but there was no ...