Micrometastases are defined by the UICC TNM Classification of Malignant Tumors as conglomerations of tumor cells measuring between 0.2 mm and 2 mm in size. Clusters of cells sized less than 0.2 mm in maximal dimension are termed isolated tumor cells (ITCs). Tumor clusters measuring larger than 2 mm are macrometastases, usually just called metastases 1. Although the official staging manuals tend to concentrate on micrometastases in lymphatic tissue, it can be applied to any tissue, e.g. liver 2.
These definitions are necessarily histopathological in scope, as in practical terms micrometastases refers to cancers that cannot be visualized on any diagnostic imaging study.
- 1. Mary K. Gospodarowicz, James D. Brierley, Christian Wittekind. TNM Classification of Malignant Tumours. (2017) ISBN: 9781119263579
- 2. Nanko M, Shimada H, Yamaoka H, Tanaka K, Masui H, Matsuo K, Ike H, Oki S, Hara M. Micrometastatic colorectal cancer lesions in the liver. (1998) Surgery today. 28 (7): 707-13. doi:10.1007/BF02484616 - Pubmed