The endoscopy went well this afternoon, and visual indications are that Sam doesn't have evidence of GvHD, but rather gastritis, probably caused by the chemo before his transplant. Straightforward to treat (but also definitely necessary to treat, as Sam's lost maybe 10 pounds over the past week). We'll hopefully get back tissue analysis from the lab tomorrow that's more definitive. Assuming nothing surprising here, I think pretty good chance we get Sam home in the next day or two. 

Also bonus: I now know what the insides of Sam's esophagus, stomach & small intestines look like! Exciting day.