A close friend of the family has cancer , but can't speak anymore? is that brain mets causing it?

It depends: What do you mean that one can't speak anymore? Do you mean -slurred speech? Hoarseness or really can't talk anymore? What kind of cancer that your close friend had? If the cancer involved the voice box, or the treatment is affected the voice box- then that will effect on her her/his ability to talk. Brain mets that is located on the areas that regulate speech also can affect one's abiity to talk.

Not necessarily: A number of problems can cause a cessation of speech but your friend's oncologist needs to know about your friend's issue and then do an evaluatain. Brain mets certainly is one of the many possibilities that the oncologist can address--but there are others so i would not rush to judgement.