Cancer of the appendix, the small pouch-like organ attached to the large intestine that supports the immune system, affects 1 or 2 people for every million people in the U.S., according to the research.
Archived version: https://archive.is/newest/https://www.independent.co.uk/news/health/appendix-cancer-gen-x-millennials-increase-b2770460.html
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I seem to remember an article saying that the appendix is used by the body to store gut bacteria, as a reserve in case the gut bacteria in the intestines are killed off by disease or something similar.
True, and it seems to also have function in the immune system.