In bioanalysis of tissue specimens, there are two main options for long-term sample storage: formalin-fixed paraffin-embedded (FFPE) samples and frozen samples. An editorial article by Caitlin Smith, (found here) nicely outlines the benefits and detriments of each. Though FFPE samples are preferred for immunostaining and morphology, she concludes that frozen samples are preferable to FFPE samples for molecular analysis and native morphology for several reasons. Foremost among them is the higher potential for quality degradation during preparation and storage. Frozen specimens, which do not suffer the same degradation, are particularly necessary for analyses involving mass spectrometry, quantatative real-time PCR, and Western blotting.