Stress may or may not be a factor in bc but it's not a good thing generally. Cancer can bring out a lot of stuff that otherwise gets buried. While having treatment, we are usually fully occupied (if not too tired to care). Afterwards there can be a bit of angst coming home to roost. Luckily I didn't have family matters causing distress, but I found counselling immensely helpful in sorting out my new normal. Your new normal would be very good if it cut out unhelpful stress so do give counselling a try. Think of it as training for a new role/life.