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If you got an answer, I assume that it is that the likelihood that acid reflux is an indication of any metastasis is quite low. And a single episode of acid reflux would be even more remote as an indication of any metastasis.
On the other hand, the stress on the body of dealing with cancer will commonly lead to an acid irritation syndrome, so it is common that someone dealing with cancer will also need to use a medicine to suppress stomach acid to ease such problems.