PubMed offers the option of limiting a search to a specific subject by using built-in subsets. Cancer is one of the subsets available and the strategy used to create it is regularly revised and updated to maximize relevant retrieval. Here is the description of the Cancer Subset: “This strategy uses terms from the Neoplasms and related branches of MeSH (Medical Subject Headings), cancer-related text words, and MEDLINE journal titles. It was created jointly by NLM (National Library of Medicine) and the National Cancer Institute to facilitate searching for subjects in all areas of cancer, ranging from clinical care to basic research.”

This subset can be used in a PubMed search as cancer[sb].  Example: “health care disparities” AND cancer[sb]

You can also search for a concept (“health care disparities”) and then limit the results to the cancer subset using the filter options in the left sidebar of the database. Both of these methods achieve the same results.