Biological behaviour and clinical implications of micrometastases

Background: The most important prognostic determinant in cancer is the identification of disseminated tumour burden (metastases). Micrometastases are microscopic (smaller than 2 mm) deposits of malignant cells that are segregated spatially from the primary tumour and depend on neovascular formation (angiogenesis) to propagate. Methods: The electronic literature (1966 to present) on micrometastases and their implications in malignant melanoma and epithelial cancers was reviewed. Results: Immunohistochemical techniques combined with serial sectioning offer the best accuracy for detection of nodal micrometastases. Molecular techniques should be reserved for blood samples or bone marrow aspirates. Detection of micrometastases in regional lymph nodes and/or bone marrow confers a poor prognosis in epithelial cancers. The concept of sentinel node biopsy combined with serial sectioning and dedicated screening for micrometastases may improve staging procedures. Strategies against angiogenesis may provide novel therapies to induce and maintain micrometastatic dormancy. Conclusion: The concept of micrometastases has resulted in a paradigm shift in the staging of epithelial tumours and our overall understanding of malignant processes.