It's not common to use "ground breaker" as a noun. It's often used as an adjective"This is a ground-breaking product" or "She has a ground-breaking idea." I don't know how to say that in Spanish, but the meaning is that something is completely new and revolutionary, nothing like it has existed before.

i have found in a dict "break ground " to mean: empezar/preparar el camino, as i didn't know the word, assunming that groundbreaker comes from this verb, you could use: pionero. I am not quite sure, although i may understand the concept in english. in any case, you can exlain the meaning to me and i'll look for something more specific. Probably spanish has not a term for this and we use some periphrasis.

no es "revolucionario?" :P según http://www.spanishdict.com, es como "iniciación de una obra, colocación de la primera piedra."