Trametinib, Fluorouracil, and Radiation Therapy Before Surgery in Treating Patients With Stage II-III Rectal Cancer

Trametinib will be given for 5-day lead-in period by mouth daily Monday-Friday starting at day -14 through -10 and concurrently for the duration of radiation therapy (approximately days 1-38).The dose of Trametinib will be escalated: 0.5 mg, 1.0 mg, 2mg. If the 2 mg dose level causes DLT (dose-limiting toxicity)in 2 out of 6 patients and the 1mg dose level was acceptable, then a 1.5 mg dose cohort will be used.

Will be administered as a continuous infusion over 120 hours at a dose of 225 mg/m2/day on Monday to Friday of every week starting day 1-38.

Radiation therapy will be delivered to the pelvis during (approximately) days 1-33 (five days a week, Mondays through Fridays for 25 fractions) using a 3-field or 4-field 3-D conformal plan to the primary tumor, surrounding soft tissues, and at risk lymph node stations (peri-rectal, presacral, internal iliac, with or without external iliac) to a total dose of 45 Gy in 1.8 Gy daily fractions. A boost radiation field will be delivered during (approximately) days 36-38. The boost will encompass the primary rectal tumor and involved lymph nodes with a 2-2.5 cm margin, which should include the presacral space. The boost dose will be 5.4 Gy in 1.8 Gy fractions for a total dose of 50.4 Gy.