The MSigDB Oncogenic Signatures  ontology contains gene sets relevant to cancer.
Statistics can now be found in the footers of each table in the GREAT web output.
All ontology data was downloaded and built between June 2013 and March 2014.
Subramanian, A., et al. Gene set enrichment analysis: a knowledge-based approach for interpreting genome-wide expression profiles, Proc Natl Acad Sci U S A. 2005 Oct 25; 102(43):15545-50.