Having anonymity is never an excuse for allowing behavior you would otherwise not in person. The internet is simply another form of (instant) communication; you wouldn't yell out "hope you get cancer!" over the phone to someone, etc.
On the same subject; go to a meeting of cancer survivors/family of cancer survivors, and say something with the phrase 'cancer' in it. See if anyone there is OK with using it as a descriptive modifier for your sentences.
When you experience life, you (usually) start to gain more appreciation and humility and compassion for others and their own struggles as well. Cancer isn't a joke, it's a serious disease that plagues millions just in the US.