You need to live or you don't. It's up to you on how you want to deal with cancer. Cancer patients have a better chance to communicate with their family members because they have a longer time to talk about their illness. It's different from someone who dies of a heart attack. Often, people need the time to talk about how they feel about their family members.
Cancer gives people a chance to do that.
Discuss the illness right away. The sooner the better. The family needs to know. The family is paramount. The family is the most important thing.