Sentinel lymph node biopsy in melanoma: a micromorphometric study relating to prognosis and completion lymph node dissection.

BACKGROUND

Sentinel lymph node (SLN) positivity has been found to be strongly associated with a poor prognosis in melanoma.

OBJECTIVES

This large referral centre study was conducted: (i) to confirm the powerful prognostic value of SLN biopsy (SLNB); (ii) to correlate patient prognosis to the micromorphometric features of SLN metastasis in SLN-positive patients; and (iii) to correlate these micromorphometric features to the likelihood of positive completion lymph node dissection (CLND).

PATIENTS AND METHODS

SLNB was performed in 455 cases of primary melanoma between January 1999 and December 2004; for patients with positive SLN, the following micromorphometric features were registered: size of the largest metastasis (two diameters), depth of metastasis, number of millimetric slices involved, maximum number of metastases on a single section, presence of intracapsular lymphatic invasion and extracapsular spread. Kaplan-Meier survival curves were compared with the log-rank test; multivariate analysis was performed using a Cox regression model. Dependence of CLND status on micromorphometric features of SLN was assessed by the chi(2) test and predictive values of the different features were evaluated by multivariate analysis using a logistic regression model.

RESULTS

A positive SLN was identified in 98 of our 455 cases. Survival was significantly shorter in SLN-positive patients than in SLN-negative patients. Extracapsular invasion was found to be an independent prognostic factor of disease-free survival; ulceration of the primary and the maximum diameter of the largest metastasis were identified as independent predictive factors of disease-specific survival. Age and the lowest diameter of the largest metastasis were identified as independent predictive criteria of positive CLND, whereas depth of metastasis was not. Positivity of CLND was not significantly associated with a worse prognosis.

CONCLUSIONS

Our study confirms the previously demonstrated strong prognostic value of SLNB. It also confirms the relationship between tumour burden in the SLN (evaluated by the maximum diameter of the largest metastasis) and clinical outcome. We point out a new micromorphometric feature of SLN, which seems to be predictive of CLND status: the lowest diameter of the largest metastasis.