Patients with rectal cancer who are candidates for pre-operative radiation therapy may be enrolled in the Phase I, single center study. Patients will have a full blood count, biochemistry, urinalysis, and ECG for safety evaluation. Sequential cohorts of three patients will be given increasing doses of oral topotecan and fixed doses of concurrent radiation (45 Gy) over five weeks. The starting dose of oral topotecan is 0.25 mg/m2 to be concomitantly administered with radiation (45 Gy) x 5 days every week unless the radiation is interrupted for Holidays/Weekends or toxicity requiring treatment delays occurs. A total of 25 doses are planned.

Inclusion Criteria:

• Patients with histologically confirmed rectal cancer.
• Candidates for preoperative radiotherapy.
• Primary tumor at least 3cm and clinical stage of T2, T3, or T4 and any N according to the Astler-Coller modification of the Dukes staging system.
• Eastern Cooperative Oncology Group (ECOG) performance status less than 2.
• Diagnosis of rectal cancer should be no more than 90 days from start of therapy.
• Evaluation at the H. Lee Moffitt Cancer Center.
• Recovery from prior surgery and life expectancy at least 3 months.

Exclusion Criteria:

• A primary tumor totally excised.
• Recurrent rectal cancer that failed initial treatment.
• Exposure to topotecan, infection, immunodeficiencies, conditions of the gastrointestinal (GI) tract which would affect absorption, medication that maintains motility/gastric emptying.
• Any concomitant malignancy within the last five years.
• Severe medical problems unrelated to the malignancy which would limit compliance with the study.
• Patients of child bearing potential.
• Not practicing adequate contraception.
• Patients who are pregnant or lactating.
• Use of an investigational drug within 30 days or 5 half-lives of the first dose.