Who is 'people'? They're not the same set, not all of cancer research is looking at people currently 'dying from cancer', nor are there going to be enough from different demographies declaring 'I am concerned about dying from cancer more than my privacy' and volunteering their data. And even if there were, that trait itself is probably skewing your data and not necessarily generalisable to people not (so particularly) concerned about 'dying from cancer'.
It would be useful to have control data sets as well, from those without cancer/illness. This is a problem in a lot of medical research where those affected with an ailment are much more likely to share data, participate in trials, and donate their bodies to science than healthy individuals are.