That's the problem with cancer when it spreads and becomes mestatic, it is virtually impossible to get rid of it as there are often hidden cancer cells waiting to erupt. Of course there are very rare situations where people live stable or even NED for a long time. But it's rare and even rarer when the primary diagnosis is lung cancer and when it has spread to everywhere including the brain. Once it hits the brain it's extremely difficult to get rid of.I guess my non medico brain can comprehend if there is surgery and tumours removed and then further treatment, it could give NED results. But with just treatment, where does the remnants of the tumour go after treatment has killed it? Does it get absorbed by the body or something? Or is it still there, just dormant?