Letter of Recommendation Question?

A lot of universities require 2 letters from college professors for transfer admissions. I worked extremely closely with an academic oncologist the past two summers doing research. Would getting a letter from him suffice as 1 of the 2 letters? His official title is technically Assistant professor of oncology at a major research university (but at the med school, not undergrad).

Or does the letter have to be from a professor whom I took a class with over the school year?

I believe this question would be best answered by the admissions office at one of the schools you are interested in applying to. From my knowledge, the schools require a letter of recommendation from a professor whom you have taken a class with and has given you a LETTER grade. Best of Luck.