There has been so much discussion about the changes happening with the new PubMed interface I think new about the subject subset strategies being updated kind of got lost in the noise.
Each year the subject subset search strategies are reviewed to determine if modifications are needed. These modifications can be something like changing MeSH, adding or deleting terms, or changing parts of the strategy to optimize retrieval. According to the NLM Technical Bulletin February 5, 2010 post, the Bioethics, Cancer, and Toxicology were revised. Complementary Medicine and Space Life Sciences are next on the list to be revised in the future. The PubMed Subset Strategies page has already been updated reflecting the changes to the three terms.
It is probably a good idea to check this page out anyway to make sure your search strategies for Aids, Complementary Medicine, Systematic Reviews, etc. are up to date and you are getting the most out of your search. Obviously these strategies aren’t for every search on Aids or Cancer but if you need to do a massive comprehensive search or if you are looking for ways to expand your search this is a great resource.