The number of U.S. registered clinical trials using stem cells increased from 709 at in summer 2007 to 2,319 today. For trials using stem cells in heart disease grew by 110% last year (from 118 to 56); Parkinson’s disease fell by 100% last year (from 1 to 0). That’s according to an index of clinical trials just posted by Stanford’s Chris Scott.

Scott examined used the world’s largest registry of clinical trials to see how many included the term stem cells, categorized them, and then compared results between two years. Not surprisingly, the vast majority of trials were in hematology and oncology indications, for which bone marrow transplants, which contain stem cells, have been practiced for generations. One comment notes that as little as 5 years ago, all such trials would have fallen under that indication.

Scott offers caveats for his analysis. In particular, not every hit in a text search need be real. Nonetheless, the numbers are fascinating.

One category the analysis does not explore is trials using fetal stem cells. Those that I know of are all for neurological indications, and at least three have received or asked for regulatory approval to start trials within the twelve months. (The trials that have been given the green light are StemCells and ReNeuron.)

Given reports that a boy developed tumours in his brain and spinal cord after an unregulated (and highly criticized) stem cell procedure, this would be an interesting category to watch. In fact, just days after the reports came out, the FDA told NeuralStem to put its plans for a clinical trial on hold.

As research on all types of stem cells grows, it will be very interesting to see how the mixtures of cell types and indications studied shifts.