Background: RAS mutations confer radiation resistance in rectal cancer, with very low pCR rates, below 5%. Midostaurin is an oral, multi-target TKI, FDA-approved for FLT3 mutated leukemia, that sensitizes colorectal tumors to radiation, and more pronounced in RAS mutant tumors through inhibition of PKCα. The purpose of this study is to establish the MTD of midostaurin with 5-FU-based CRT for locally advanced rectal cancer and explore the efficacy based on genotype. Methods: Patients with MRI or ultrasound defined T3 or T4 or node+ adenocarcinoma of the rectum and without evidence of metastatic disease were enrolled an IRB-approved protocol (NCT01282502). Patients received infusional 5-FU 225 mg/M2/day continuously. Standard radiotherapy was administered to 50.4 Gy in 28 fractions. Midostaurin was given on days of radiation twice daily. Dose was escalated in a 3+3 design: dose level 1 was 50 mg BID, dose level 2 was 75 mg BID. TME was performed 6-9 weeks following the completion of chemoradiation. Genotyping was performed using whole exome sequencing, with either blood or adjacent normal tissue normal control. Results: 19 patients were enrolled from October 2011 through November 2016. 3/19 patients were female; median age was 53 years. Clinical stage: 5/19 stage II, 14/19 stage III. The MTD was declared at 75 mg BID. All 19 patients completed therapy and underwent resection. At least one grade 3-4 toxicity occurred in 9/19 of patients. The most common Gr 3+ toxicity was lymphopenia (5/19) and rash (3/19) The pathologic complete response (pCR) for all patients completing study therapy was 3/19. R0 resection was achieved in all 19 patients. With a median follow up of 3.0 years, two patients had recurrence- both had synchronous local and distant. DFS at 3 years is 89.5% (CI 75.7-100%), and OS-3 was 87.7% (CI 71.6-100%). 16/19 tumors have been sequenced: KRAS mutant 2/16, NRAS 3/16, BRAF 3/16. Genotype of pCR patients: 2/3 RAS mutant, 1/3 not sequenced yet. Conclusions: Midostaurin combined with chemoradiation is well tolerated. Final genotyping results and correlation of RAS status and pCR will be presented at the meeting. Clinical trial information: NCT01282502