Paradigm of metastasis for melanoma and breast cancer based on the sentinel lymph node experience.

Lymph node status is the most reliable prognostic indicator for patients with melanoma and breast cancer. Because it is the first node draining the primary cancer, the sentinel lymph node (SLN) is most likely to harbor metastatic cancer cells. The Breslow thickness of the primary melanoma and the size of primary breast cancer are highly correlated with SLN metastasis. If the SLN is negative, its negative predictive value for the remaining nodal basin exceeds 95%; thus, survival rates for melanoma and breast cancer increase when the SLN is negative. The rate of SLN identification is more than 95%, and the false-negative rate is about 5%. SLN data from melanoma and breast cancer are so convincing that they have been incorporated into the new American Joint Committee on Cancer classification of these cancers. The therapeutic value of additional lymph node dissection after a positive SLN for melanoma or breast cancer is still controversial. In melanoma, a 3-year follow-up may confirm better survival when the SLN is negative. However, about 25% of histologically negative SLNs may be upstaged by molecular techniques, and patients whose SLNs are positive by polymerase chain reaction (PCR) assay may develop recurrence. In most cases, melanoma and breast cancer follow an orderly progression of metastasis to the SLN; however, a small subgroup may develop systemic dissemination without SLN involvement. Current SLN experience has confirmed that the earlier the cancer, the less its potential for metastasis. Since treatments for metastatic cancer are still limited, early detection and resection are imperative. Better understanding of the molecular and genetic mechanisms of metastasis will be critical to select high-risk patients for adjuvant therapy.