How is the UMass MD-PhD Program structured with regard to integration of the two degrees?

The typical program structure is 2 1/3 / 3-5 / 1 2/3 where the students begins by completing the pre-clinical medical education, plus one thematic section in the clerkships, shifting to the graduate school for the PhD studies and returning to finish up to two clinical years of Medical School. However, the Program is flexible enough to accommodate changes based on a reasonable request.