micrometastasis

Micrometastasis refers to the presence of small clusters of cancer cells that have spread from a primary tumor but are too small to be classified as macrometastases. In many cancer staging systems, micrometastases are defined as deposits measuring between about 0.2 millimeters and 2 millimeters in diameter. Deposits smaller than 0.2 millimeters are often described as isolated tumor cells. Micrometastases can be found in lymph nodes, distant organs, or other tissues.

Detection of micrometastases relies on detailed histopathological examination, often with immunohistochemical staining or molecular techniques to identify tumor cells that are not visible on routine sections. Sentinel lymph node biopsy is a common method for detecting nodal micrometastases in certain cancers, particularly breast cancer and melanoma. The identification of micrometastases may require serial sectioning and enhanced staining to increase sensitivity.

The clinical significance of micrometastases varies by cancer type. In some cancers, their presence influences staging and can alter treatment decisions, such as the use of adjuvant systemic therapy. In others, micrometastases may have a limited or uncertain impact on prognosis, and their management remains a topic of ongoing research. Not all micrometastases progress to overt metastatic disease; some may remain dormant or regress.

Limitations and controversies include variability in definitions, differences in detection sensitivity, and divergent guidelines across cancer types. The interpretation of micrometastases is thus context-dependent, requiring integration of tumor biology, patient factors, and established clinical guidelines.