Malignant melanoma: from cell kinetics to micrometastases.

Malignant melanoma (MM) micrometastases are basically seen in three locations inside the peritumoral dermis. They are localized (i) inside the interstitial sector of the dermal stroma; (ii) abutted to the external surface of the microvasculature; and (iii) more rarely present inside vascular channels. Single-cell and paucicellular micrometastases may be disclosed using immunohistochemistry even in the absence of larger microsatellites, which represent micronodular nests of metastatic cells. The presence of microsatellites is frequently tied to markers of MM aggressiveness including thickness and the Ki-67 index. Micrometastases may be present in the same conditions, but even as early as thin MM showing a small growth fraction. Microsatellites as well as micrometastases appear to predict locoregional extension and decreased relapse-free interval, but not distant metastasis and overall survival. These considerations have implications for patient care since patients with microsatellites and micrometastases are now included in the clinical stage III category of the disease. Their implication as a prognostic factor is not fully dependent on or linked to other markers of MM aggressiveness.