Can ultrasound detect adenocarcinoma of the stomach?

Not typically: Evaluation of the stomach is not in the usual realm for ultrasound scrutiny. I imagine that in certain cases a significant gastric tumor might be detected but in real practice we would probably detect metastatic lesions in the liver from the stomach cancer rather than the tumor itself.

See answer: Upper endoscopy (with a scope) or upper GI (with oral contrast and x-rays) are preferable ways of evaluating the stomach for adenocarcinoma or other gastric pathology. Ultrasound is not an ideal modality for this purpose.