Sentinel lymph node biopsy in patients with T1a cutaneous malignant melanoma: A multicenter cohort study

Background: Sentinel lymph node biopsy is not routinely recommended for T1a cutaneous melanoma due to the overall low risk of positivity. Prognostic factors for positive sentinel lymph node (SLN1) in this population are poorly characterized. Objective: To determine factors associated with SLN1 in patients with T1a melanoma. Methods: Patients with pathologic T1a (\ 0.80 mm, nonulcerated) cutaneous melanoma from 5 highvolume melanoma centers from 2001 to 2020 who underwent wide local excision with sentinel lymph node biopsy were included in the study. Patient and tumor characteristics associated with SLN1 were analyzed by univariate and multivariable logistic regression analyses. Age was dichotomized into #42 (25% quartile cutoff) and[42 years. Results: Of the 965 patients identified, the overall SLN1 was 4.4% (N = 43). Factors associated with SLN1 were age #42 years (7.5% vs 3.7%; odds ratio [OR], 2.14; P =.03), head/neck primary tumor location (9.2% vs 4%; OR, 2.75; P =.04), lymphovascular invasion (21.4% vs 4.2%; OR, 5.64; P =.01), and $2 mitoses/mm2 (8.2% vs 3.4%; OR, 2.31; P =.03). Patients \ 42 years with $2 mitoses/mm2 (N = 38) had a SLN1 rate of 18.4 % Limitations: Retrospective study. Conclusion: SLN1 is low in patients with T1a melanomas, but younger age, lymphovascular invasion, mitogenicity, and head/neck primary site appear to confer a higher risk of SLN1. ( J Am Acad Dermatol 2023;88:52-9.)