The whole point of the dataset was the molecular side. Gene expression, copy number changes, and mutations.
These (and others) molecular traits differ between gender, race, and age. An over representation of a specific gender or race might affects the effectiveness of the developed therapies towards other gender/race combinations.
This visualization is meant to show at a glance how these clinical variables are currently distributed in one of the most used and relevant cancer data-sets.
The people at The Cancer Genome Atlas did a great job, but much more has to be done to achieve the ambitious goal of Precision Medicine and have therapies personalized to each one genetic makeup.
Even weighting the tissue types by actual incidence rather than number of samples would be far more interesting.
I was one of (many many many) co-authors on several TCGA consortium papers, so I'm quite familiar with it, and with the challenges going forward, but this visualization addresses none of those challenges.