The expiry date of any pharmaceutical product depends on what is in it. Most chemicals that are used will not deteriorate over the space of a year or two, however if the cream contains other things, such as antibiotics, extracts from animals (eg placenta extracts etc) then it is advisable not to use it.

I think that the main danger is not that the ingredients in the cream are harmful, but that after being opened it is no longer sterile and could contain bacteria or something. If it were only a year or two I would say that there is no danger using the cream, but if it is 10 years I would recommend that you throw it away.

FYI, check out this web site, it lists the ingredients in Neutrogena hand cream.