Polis Massa used to be a real planet. It had a civilization and everything. Then it blew up, or was destroyed or something. The natives all died, and the planet was reduced to asteroids. At some point, someone went there and built a space station complete with a medical center. Someone must have been making money off of it, since it remained fully staffed and operational- maybe a bit out of date. The most notabel thing about the facility is that they refused treatment to noone and did not require patients to fill out any forms. Obi-Wan Kenobi met Yoda there after defeating Darth Vader. Pade Amidala died giving birth to Luke Skywalker and his sister Leia on Polis Massa. After that, the Rebel Alliance used it as a base for a little while, and it was one of the 47 different places where plans for the Death Star were intercepted.
Luke and Leia were born there, but neither stayed long. Pade died there. Other than that, there were some droids and aliens there.