Welcome to the club no one wants to be a part of. Try not to get ahead of yourself. You don't know the treatment plan yet, so it is hard to make a decision about work. Listen, take notes, and ask questions. Bring someone with you to all appointments. Another set of ears is good.
When I was diagnosed in 2014, I happened upon this site. You will find excellent support here. You can ask questions,vent, be angry, whine, and throw tantrums. No one will judge you. We have all traveled down your road. Try to be positive. Breast cancer treatments have come so far, so you will beat it.