This is from an earlier post of yours elsewhere:
"My question is, if it were a pancreatic cyst, would have it shown on the ultrasound?"
Probably yes. Here's a paper from a radiologists' journal:
Transabdominal Ultrasound Detection of Pancreatic Cysts Incidentally Detected at CT, MRI, or Endoscopic Ultrasound
"The overall detection rate of [pancreatic cysts using ultrasound] was 88.3%..."
From you again:
"Is there a possibility of it not showing?"
Smaller cysts, and those in certain regions of the pancreas, are less detectable.
But why think of the pancreas rather than the stomach? That seems more likely, especially with the occult blood found.