For me, it's my Cancerversary. That will never not be weird to say.
Everyone defines their Cancerversary as something different. Some people it's the day they're diagnosed, Some call it the day they started treatment. I like to call it my last day of that chapter, the day I had my surgery to remove that pesky, sketchy uterus. For me, it's a day to celebrate.
It's also a day to remind everyone to go to the doctor. Check your boobs. Check your prostate. If you've got a vagina, get your PAP done regularly (they say you can do it every 3 years now if you haven't had an abnormal result, so yay!). I know it's uncomfortable and it sucks but lemme tell you not catching cancer early enough to do something about it sucks way worse. Take care of yourselves, and encourage the people you care about to take care of themselves.
Tell people you love them. Give your pets extra pats for me. Eat that extra piece of cake. Enjoy life while you can.
Related: go vote so people can have healthcare for this kind of shit.