One of the most important roles of cancer chemotherapy is as adjuvant therapy to eradicate or suppress minimal residual disease after primary field treatment with surgery or irradiation. Failure of primary field therapy to eradicate tumor is due principally to occult micrometastases of tumor stem cells outside the primary field. These distant micrometastases are more likely to be present in patients with positive lymph nodes at the time of surgery (eg, breast cancer), in patients with tumors known to have a propensity for early hematogenous spread (eg, osteogenic sarcoma, Wilms’ tumor), and in patients with certain pathologic or molecular risk factors (eg, high proliferative index, vascular invasion, oncogene amplification). Given specific risk factors, the risk of recurrent or metastatic disease can be extremely high (> 80%). Only systemic therapy can adequately prevent micrometastases.
