It may not be related to the Casodex, but I would certainly want to immediately get him in to see a Gastroenterologist. The esophageal varices can be life threatening if one happens to break and start leaking. There are ways to examine them and to treat them if active bleeding is confirmed.
The esophageal varices often develop as a result of livers that have been damaged by chronic viral diseases or other liver traumas. This can result in an over-pressure in the portal vein, and the nearby veins in the esophagus and stomach. They swell up, and can eventually leak or burst.
I'd want to stop the bleeding first. Then treat anything dangerous in the the liver. Then resume/continue prostate cancer treatments.
If he already had esophageal varices he most likely already had a liver problem. However, bleeding and black tarry stools with the varices could be life threatening. Call his doc ASAP.
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