Well I hope other people will answer because I am curious...I had all 3 from pathologists (plus my deans letter). That was basically because I did a post soph fellowship and the physicians who knew me best were pathologists. I thought about getting an LOR from either a surgeon I knew pretty well or an IM person who seemed to like me so much I thought he was going to kidnap me and give me the Clockwork Orange treatment until I agreed to go into IM. He was one of the folks who told me I was "wasting a talent" by not doing an IM residency. (My talent is that old people like me). Unfortunately, which I did not tell him, having old people like you does not really help pay the bills unless you are in the religion business, because old people do not spend money on anything unless it is grandchildren or god. Not to say that I am in this for the money, it's because IM involves too much peripheral stuff for me. If it was all challenging diagnoses and being nice to old people, well sign me up. Instead it's paperwork, avoiding diagnostic tests, and arguing with people over appointments or costs. That and sticking your finger up someone's butt to look for the cancer.
But anyway, to be back on topic I had 2 letters from pathologists at my home institution, where I did the PSF. One was the residency PD and the other was the director of AP, both of whom had lots of contacts, etc. The other was a bigwig at an away institution where I did a rotation.
The consensus seems to be that you need at least one letter from a pathologist who can specifically attest to your ability and motivation to do pathology. If you have done lots of research, probably a letter from there. But if you have an IM or pediatrician who knows you really well and can write you a letter, go for it. ERAS allows you to send usually 3 letters + deans letter to each program, but they don't have to be the same letter. Thus you can send different letters to different programs if you think it would be helpful.
