Pathological specimens used in molecular pathology
The working material that is generally used in pathologies is formalin-fixed paraffin-embedded tissue. Since a high tumor cell content is very important for molecular analysis as the allelic fraction of variants can be in the range from very low (around 5 %) to very high (100 %), the pathologists mark the tumor areas on hematoxilin-eosin stained slides and estimate the tumor cell content in these areas. Nucleic acids, DNA as well as RNA, can both be isolated from these tissues after deparaffinization by macro-dissection of the tumor area(s) from unstained sections of tissue slides and used for a diverse spectrum of techniques. The increase in biomarkers being tested presents new challenges to molecular pathology as the available material becomes more limited. Figure 1 depicts the change in the need for biomarker testing compared to tissue availability and thus available nucleic acids.
