I can't remember the percentage for me. I know it wasn't big but big enough to make me go with it. Only you can choose what you can live with - not your oncologist, nor your husband, nor anyone else. Do remember that you can start down the path of chemo and stop if it gets too much.
This is a question that comes up from members every now and then and I think that the inimitable @allyjay puts it really well (so well that I bookmarked this response ages ago):
"Purely on the statistical side, for me, when faced with the same decision as you now are, I looked at it from different angles. One of the scenarios for me was this. I was in a room with 1000 women who were told that they had been diagnosed with my type and grade of breast cancer. We were all told to have such and such surgery, which we did. We were then taken back to that same dreaded room and given a card with a number. Then 830 numbers were read out, and those women were allowed to leave the room and go next door for a celebratory cup of tea and slice of cake....considered cured (10 years). The other 170 shocked women looked at each other with dread. Just then the compere said...."Oh sorry, I forgot, I have another 70 numbers to draw, that is the women who had additional chemo, they can pick up their bags and join the others". If, perchance I was one of the 100 left behind to the future of stage four, would I wish that I might have been one of the other 70, or would I go "Que Sera Sera..." and accept it? For me the answer was "Fuck no" bring it all on, and if the wheels still fall off, at least I would have given it my best shot, and not have been left with the perhaps..." Each of us has to weigh it all up, make our decisions and then go forward. As Afraser says, having started chemo, you can always stop. But it doesn't work the other way. Best of luck."
Good luck with whichever path you choose @dada