my father had acid reflux off and on his whole life, but nothing a few Tums wouldnt handle. Then in 1997 he got it so bad he couldnt sleep for weeks. The doctors kept giving him antacids, to no avail, and finally they decided his gallbladder was to blame. They performed surgery and found the GB was fine - but his pancreas had three tumors. He died less than a year later in a Whipple surgey (removal of most or all of pancreas)

So i think, yes, severe acid reflux can be a sign of cancer - pancreatic, and maybe other forms (liver, stomach, etc)