Small lesions of breast or colorectal origin have been eradicated with 5-fluorouracil (5-FU) therapy and did not recur after the chemotherapy was discontinued. This has not occurred in larger lesions. It is preferable to treat patients with known remaining disease early rather than to wait for them to become symptomatic which often renders them poor risk for effective chemotherapy. In patients having curative resections for gastrointestinal, breast, or testicular cancers that are high risk for developing recurrence, adjuvant chemotherapy appears promising.