I can't say anything about the management of the Pan-Mass Challenge, but I did look up the Jimmy Fund / Dana Farber Cancer Institute on Charity Navigator, and Dana Farber is rated as a 4-star charity (which is the highest star rating).

I've been using Charity Navigator to check out organizations before giving them money. Their stated purpose from their home page, for whatever it's worth - "Charity Navigator, America's premier independent charity evaluator, works to advance a more efficient and responsive philanthropic marketplace by evaluating the financial health of America's largest charities.".

--- Denise