I am trying to run an IHC analysis of my CAM-tumour tissues. Since my tumour on CAM was extremely small and difficult to slice at the right position, I pre-embedded my sample in 5% agarose with a fixed orientation. Then I proceeded with the following tissue processing for paraffin embedding. However, these agarose-pretreated samples showed negative signals after IHC staining. Since I didn't change the protocol and antibody dilution for my experiment, I doubt that the agarose affects the IHC staining process. Has anyone come across the sample problem? I would really appreciate it if you could offer any suggestions. Thanks in advance.