Lymph node metastasis is the most important predictor of prognosis, af
ter surgery, in colorectal carcinoma. The term ''micrometastasis'' has
evolved from a morphological definition to one that is used with mole
cular-based techniques. We review the literature to evaluate the signi
ficance of detecting micrometastases in colorectal carcinoma, either b
y morphological or molecular techniques, and address technical difficu
lties encountered with both. Routine use of immunohistochemistry is no
t recommended as most studies show little change in staging or prognos
is. Radioimmunoguided surgery may prove beneficial, but problems of fa
lse positives in benign diseases need to be addressed. Immunohistochem
ical detection of micrometastatic deposits in bone marrow aspirates ho
lds the most promise for clinical practice. Molecular techniques are m
ore sensitive than immunohistochemistry, but prognostic value needs to
be determined. Molecular diagnostics can also determine genetic alter
ations and mutations that should improve our understanding of metastat
ic colon cancer and staging accuracy. (C) 1998 Wiley-Liss, Inc.