http://groups.google.com/advanced_group_search

type alt.support.cancer in the "Return only messages from the newsgroup"
box
(I usually start by sorting by date, depending on the search words or
phrase)

In the case of (for instance) Astrocytoma, I would limit the search to 3
months first to see who the most recent posters are, then re-search
under each poster's name to follow their progress and/or find them on
the newsgroup and read their recent posts.

Then I might search further back, so change the time criteria to
"anytime".

This is just one example of how to search the archives.
J