There are some who say in the age of the Internet you need to grow a thick skin - that may be a bit true but it also should not be used as an excuse to allow people to say or do things are are quite frankly offensive to reasonable people.

However - they need to be told that it is offensive or they will never know better. That means you need to stand up and politely let them know (in a private IM also so as to not attract undue drama). If they decide to take it the wrong way then so be it - blacklist them and be on your way. If they then harass or incite other harass you (as you have blacklisted them) then report them for said harassment.

Most of the time people use these words because they incorrectly think it is cool and the adoring masses find them amusing - most people will react kindly to a "hey can you throttle back on the cancer stuff as my mum is has cancer and may not live - it's no joke" those that do not are most likely not the sort of people you will want to be around anyway.