The important question is how it affects YOUR quality of life and if the side effects are worth the benefits for you. Different people react differently.

From what you've said before, it seems like Enhertu is working on your cancer. Statistically, LenPem may work just as well on the total population, but it may or may not work for you. And the side effects may be better or worse.

If it were me, I'd stick with the Enhertu until it stopped working, unless I felt that the quality of life was unacceptable. Better the devil you know.