My Husband Has Lung, Brain, Brain Stem And Spinal Cord

My husband has lung, brain, brain stem and spinal cord cancer.
He is vomiting a lot. His oncologist has given him medication for this. It seems to make him sicker.
Now my question:
Recently he is throwing up a white milky fluid.
Do you have any idea what this is?

Side note:
I have check on line (no luck). His doctor is very hard to reach.

Thank you in advance,
Shilo