How do i get my mom to understand?

You're hoping for more from your mother than her past history shows her being able to give. Quite possibly she has never experienced the type of caring you need. The situation is akin to being able to sing a song requires knowing the song. While your need is very real, once more you will need to rely more on yourself and others than you can get from your mother. You realize what you need. Instead of being overwhelmed by your fear, let it motivate you to talk with your mother. On the basis of your present state, mentally you are living with cancer already. Instead, live while you can and find the joy that is available. Worry lacks the power to improve our lives or to save us. What will be, will be and we must handle each situation if it arises, not before. Keep yourself open to present comforts and joys.