Kelly Cartwright lost her leg to synovial sarcoma in 2004. She just won the gold medal for the Long Jump and the silver medal for the 100m.
Here she talks about her disease and how it lead her to athletics:
http://www.youtube.com/watch?v=2K1jMfkT90c
Here is a video about her training where she explains the difference between her regular prosthetic leg and her athletic prosthetic leg:
http://www.youtube.com/watch?v=YyyTg7Ez4fw
Here is an interview after she won the gold medal for the long jump: