micrometastatic

Micrometastatic refers to the presence of very small clusters of cancer cells that have spread from a primary tumor to distant sites but are too small to be detected by standard imaging. Micrometastases are usually identified only by microscopic examination of tissue or by molecular assays and can occur in lymph nodes, bone marrow, liver, lungs, or other organs.

Detection and classification: In pathology, micrometastases are identified by immunohistochemical staining for epithelial markers such as cytokeratins, or by molecular techniques like RT-PCR or sequencing that can detect tumor-specific transcripts. In some cancers, the term micrometastasis is part of a formal size-based classification of nodal metastases; for example, in breast cancer lymph node metastases are categorized as macrometastases (>2 mm in greatest dimension), micrometastases (0.2–2 mm), and isolated tumor cells (≤0.2 mm). Definitions can vary by cancer type and staging system.

Clinical significance: The prognostic and therapeutic implications of micrometastases are context dependent. In some tumor types, the presence of micrometastases is associated with higher risk of relapse or progression and can influence treatment planning; in others, their clinical relevance remains uncertain or they may reflect minimal residual disease that may not progress.

Biological and research aspects: Micrometastases raise questions about cancer cell dormancy, metastatic spread, and the effectiveness of systemic therapies in eradicating disseminated tumor cells. Ongoing research seeks to identify biomarkers, detect micrometastases earlier, and understand their dynamics to guide adjuvant treatment.