Incidence of sentinel node metastasis in patients with thin primary melanoma (<= 1 mm) with vertical growth phase

Background: Patients with thin primary melanomas (less than or equal to 1 m m) generally have an excellent prognosis. However, the presence of a vertic al growth phase (VGP) adversely impacts the survival rate. We report on the rate of occurrence of nodal metastasis in patients with thin primary melan omas with a VGP who are offered sentinel lymph node (SLN) biopsy. Methods: Among 235 patients with clinically localized cutaneous melanomas w ho underwent successful SLN biopsy, 71 had lesions 1 mm or smaller with a V GP. The SLN was localized by using blue dye and a radiotracer. If negative for tumor by using hematoxylin and eosin staining, the SLN was further exam ined by immunohistochemistry. Results: The rate of occurrence of SLN metastasis was 15.2% in patients wit h melanomas deeper than 1 mm and 5.6% in patients with thin melanomas. Thre e patients with thin melanomas and a positive SLN had low-risk lesions, bas ed on a highly accurate six-variable multivariate logistic regression model for predicting 8-year survival in stage I/II melanomas. The fourth patient had a low- to intermediate-risk lesion based on this model. At the time of the lymphadenectomy, one patient had two additional nodes with metastasis. Conclusions: VGP in a melanoma 1 mm or smaller seems to be a risk factor fo r nodal metastasis. The risk of nodal disease may not be accurately predict ed by the use of a multivariate logistic regression model that incorporates thickness, mitotic rate, regression, tumor-infiltrating lymphocytes, sex, and anatomical site. Patients with thin lesions having VGP should be evalua ted for SLN biopsy and trials of adjuvant therapy when stage III disease is found.