For our work, we are currently do both western blot and IHC for a lot of our targets for two reasons. The first is that is is always nice to confirm a result using two different methods, the second is that by performing experiments that give you both quantitative and qualitative data you will more likely arrive at the right conclusion... is the change in protein level homogeneous across the tumour or confined to a region specific.

Thank you for the information.But more region may be covered in heterogeneous tissue whilw performing western blot

Sorry I didn't really answer your question in my reply, You are right you can miss your target proteins using IHC, but if you think about it, you would need that small region of the tumour to have a massive increase/decrease of your target otherwise it would be diluted in the total protein of the tumour so you might not pick up any difference by western anyway.

I suggest to do both, cover all bases and then get all of the info.