Background. A consensus for which patients with thin melanomas (B≤ mm) should undergo sentinel lymph node biopsy (SLNB) is not established. We describe a large single institution experience with SLNB for thin melanomas to determine factors predictive of nodal metastases. Methods. Retrospective review from 2005 to 2010 identified 271 patients with thin melanomas who underwent SLNB, along with 13 additional patients not treated with SLNB who developed a nodal recurrence as first site of recurrence. Clinicopathologic characteristics were correlated with nodal status and outcome. Results. Median age was 55 years, and 53 % of patients were male. Median Breslow thickness was 0.85 mm. Overall, a positive sentinel lymph node (SLN) was found in 22 (8.1 %) of 271 cases; 8.4 % of melanomas ≥0.76 mm were SLN positive with 5 % of T1a melanomas ≥0.76 mm and 13 % of T1b melanomas ≥0.76 mm having SLN metastases. Only two of 33 highly selected patients with melanomas<0.76 mm (both T1b) had a positive SLN. Logistic regression analysis demonstrated that mitotic rate ≤1/mm 2 significantly correlated with nodal disease (p<0.05) and ulceration correlated with SLN metastases (p<0.05). Median follow-up was 2.1 years. Overall survival did not differ between positive and negative SLN patients (p = 0.53) but was worse for patients presenting with a nodal recurrence (p<0.01). Conclusions. SLN metastases were seen in 8.4 % of thin melanomas ≥0.76 mm, including 5 % of T1a melanomas ≥0.76 mm. We believe these rates are sufficient to justify consideration of SLNB in these patients, while the indications for SLNB in melanomas<0.76 mm remain to be defined.
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