Have you a doctor or specialist who can advise specifically in relation to your family history? The oncologist is trying to reduce your risk of cancer recurrence but you may find a decision easier if someone else with specialist knowledge can advise about the potential risks some chemotherapies may have in relation to other health factors. These risks may actually be very small but you are entitled to know about them. Your treatment is your decision but you want to make it with as much information as possible. Seeking a second, specialised opinion is just being practical. Best wishes.