Accurate Gene Expression Profiling Requires Intact RNA

Think Fresh, Not Frozen: RNARetain^® Preserves RNA Integrity at Room Temperature

Agendia is committed to providing physicians and their patients accurate and reproducible results.  With its proprietary FDA-cleared RNARetain molecular fixative, physicians have an easy-to-use method for preserving their patient’s tumor sample at room temperature. MammaPrint does not require frozen tissue. 

Fresh tissue preservation memorializes the tumor sample now and forever, thereby conserving the patient’s tumor genome. Thus, the MammaPrint gene expression profile which analyzes thousands of genes, while used for prognosis and prediction today, may also be re-queried in the future once additional predictive profiles are identified for such agents as angiogenesis inhibitors, epothilones, etc.

Gene expression profiling is designed to interpret the RNA message coded by the DNA within the cell which contains the instructions as to which proteins to make or express. The intactness of this message is, therefore, essential if the interpretation is to be correct. It is well known that the RNA message is degraded by formalin fixation. For this reason, all tissue stored by the NIH Tissue Biorepository and for many ongoing clinical trials must be stored in RNALater molecular fixative,⁽¹⁷⁾ the very same as Agendia's proprietary solution.  Only in this manner is the RNA, the cell's genomic message, kept intact and undegraded.

Comparing the RNA Integrity of fresh-fixed tissue to that of FFPE (Figure 1), note the distinct peaks captured in the fresh-fixed sample as well as the clean electrophoresis bands; these are representative of high RNA integrity, as shown with a RIN (RNA Integrity Number) of 9.7.  In fact, part of Agendia’s FDA label stipulates that the RIN must exceed 7.0 in order to perform the test.  Conversely, as discussed in the cited literature, RNA is immediately degraded upon formalin fixation as shown by the lack of distinct peaks, smears instead of clean bands, and a RIN of 2.