Now I have a huge marble/lump on my wrist. I'll probably go to a clinic just to make sure playing these pieces didnt give me cancer (joking obviously). Hopefully its nothing to dangerous. Has anyone else here experienced this? Get a weird looking marble on their wrist cause of playing piano? is it like some kind of muscle stress? And yeah the op 42, and the op. 26 polonaise are the most difficult pieces I've learned so far. Fun very fun, but...
Getting worried.
I dont want to hear the doctor go like, "yeah, were going to have to amputate that." 
Just like Jmenz said, it's most probably a ganglion cyst. Not dangerous, but can be a sign of joint misuse.
In the old days they were "treated" by hitting with a heavy book
It's possible to empty them, but they often come back. They can also be operated, but they still often recur and if one is unlucky like my friend, there can be complications from the operation much worse than the cysts, so I wouldn't recommend that unless they are really making you life difficult.
I have had them too. I had a big one as a teenager, it went away in about a year by itself. Then I got one about 5 years ago on my left wrist. I got it after getting a new bicyckle, so it was related to having a bad wrist position while cyckling. That one actually diminished after I started playing the piano and learned better wrist technique. So yes, it might be related to your playing technique. Do you have a teacher?
Topic: Shouldnt have learned the Waltz and the polonaise...