Use quotation marks (e.g. "breast cancer") to search by that exact term or phrase, no variations.
Use multiple keywords separated by spaces (e.g. kidney renal) for broader search results. This search will retrieve items that correspond to any of those words, ranking higher those with all or most of the keywords. Plurals and other variations are automatically included.
To exclude a word from your search, precede it with a hyphen, e.g. -historical