My son has metastatic cancer diagnosed Dec 2016

Since he was diagnosed, my son has had 11 chemo treatments.  After the 8th they told us the cancer hadnt spread.  We were also told when diagnosed that it was terminal.

Now, my son has decided to stop chemo treatment.  He said it wasnt worth the treatment - he was unwell for 10 days and then only 4 good days before starting over again.

My question is - what should I expect will happen now?