35. Factors predictive of clinical outcomes in patients with thin cutaneous melanoma

Abstract

<h3>Background</h3> Although the outlook for patients with thin (≤ 1mm) melanomas is generally good, a minority of patients will suffer adverse clinical outcomes (distant metastasis and death). The aim of this study was to identify clinico-pathological factors predictive of poorer clinical outcomes in a large number of patients with thin melanomas, by comparing patients with distant metastases with those who did not experience any tumour recurrence. <h3>Methods</h3> Patients with thin melanoma (≤1mm thick) were identified in the Melanoma Institute Australia database. From this group, all patients who experienced distant metastasis, and 1000 random patients who experienced no recurrences were identified. The association of clinico-pathological features with the development of brain metastasis, distant metastasis-free survival (DMFS) and melanoma-specific survival (MSS) was analysed. <h3>Results</h3> Of 5628 patients with thin melanoma, 174 experienced distant metastasis. Factors significantly associated with development of brain metastasis included: Breslow thickness 0.51-0.76mm (OR = 3.8, 95%CI = 1.1-13.7) and 0.76-1.00mm (OR = 5.2, 95%CI = 1.5-18.6), compared with 0.01-0.50mm; ulceration (OR = 4.4, 95%CI = 1.8-10.7); anatomical location in trunk vs other sites (OR = 2.4, 95%CI = 1.2-4.7); and mitoses ≥1/mm² (OR = 2.5, 95%CI= 1.2-5.5). Factors independently associated with shorter DMFS were: greater thickness (0.76-1.00mm vs 0.01-0.50mm, HR=3.5, 95%CI = 1.8-6.7); ulceration (HR = 3.0, 95%CI = 1.7-5.1); anatomical location in head/neck vs extremities (HR = 2.6, 95%CI = 1.4-4.7); and mitoses ≥1/mm² (HR=1.7, 95%CI= 1.1-2.6). Independent predictors of poorer MSS were: age >50 years (HR = 2.4, 95%CI = 1.6-3.7); greater thickness (0.76-1.00mm vs 0.01-0.50mm, HR=3.5, 95%CI= 1.6-7.5); ulceration (HR = 2.8, 95%CI= 1.6-4.9); and mitoses ≥1/mm² (HR = 2.0, 95%CI = 1.3-3.4). <h3>Conclusions</h3> Tumour thickness subgroups (0.01-0.50mm, 0.51-0.75mm and 0.76-1.00mm) are associated with significantly different clinical outcomes. Subgrouping of tumour thickness in thin melanomas should be considered in future revisions of the AJCC melanoma staging system.