Are galaxies homogeneous?

Title worded awkwardly, but I was thinking about the chemical makeup of our planet, and the other bodies in our solar system. Is the chemical makeup of our star system similar to every other star system? And if not, are we more similar to stars nearest to ours? Is it totally random? Like does every star system have roughly the same amount of iron, hydrogen, oxygen, etc. When averaged out? Has this even been studied?