If you are found to be eligible to take part in this study, you will be assigned to a specific dose of topotecan. The first group of participants will receive a smaller dose of topotecan. If patients in that group are able to recover a sufficient number of platelets by Day 22 and no severe side effects are experienced, the next group of participants will be treated with a larger dose topotecan. The dose will continue to be increased for each new group of participants until all the participants in a dose group are unable to recover a sufficient number of platelets by Day 22, or until severe side effects are experienced. There will be 3 patients in each group. The doses of all the other drugs used on this study will be the same for every participants.