Molecular staging for patients with malignant melanoma

Molecular staging of cancers hold the promise of being more accurate compared with routine histology, particularly with regard to determining regional-nodal status. With newer reverse transcriptase-PCR (RT-PCR)-based assays, sensitivities reported are as high as identifying one cancer cell in a background of a million normal cells. Although this sensitivity is 100-times what the human eye can differentiate under the microscope, the new challenge becomes determining the relevance of this low-volume disease in the regional basin, in particular, the sentinel lymph node (SLN). Patients with melanomas greater than 0.75 mm in tumor thickness participated in a research study that examined their SLNs with routine histology, immunhistochemical staining and a RT-PCR assay based on the tyrosinase probe. A total of 311 patients were involved in the study and patients whose SLN were negative from all three assays for metastatic disease had a good survival, with a 92% disease-free survival (DFS) and a 97% overall survival (OS) regardless of the tumor thickness or the ulceration status of the primary melanoma. Patients upstaged with the RT-PCR assay had a significantly decreased DFS and OS compared with patients who were SLN negative. Patients who had enough tumor burden in the SLN that allowed their metastatic disease to be identified with routine histology had a 48% recurrence rate at 5 years. A recently published meta-analysis confirmed that molecular staging of the SLN in melanoma contains important prognostic information. Micrometastatic disease missed by routine histology in the SLN in melanoma patients is clinically relevant disease. Molecular staging has the potential of providing a more accurate staging in the SLN, for prognostication and directing adjuvant therapies.