LE-SN38 will be administered IV over 90 minutes. At least three patients will be studied at each dose level and at least three patients will complete one 21-day course before any patient is enrolled at the next dose level. Study drug administration will continue on an every 21-day schedule in the absence of progressive disease or unacceptable toxicity. A subsequent course of treatment may be administered at least 21 days after receiving a prior dose of LE-SN38 when study criteria are met.