Capabilities for quantitative mass spectrometry–based proteomic profiling of formalin-fixed archival tissue have been developed. Using Liquid Tissue reagents and protocols, we have effectively profiled and validated known and novel cancer biomarkers across a wide variety of fixed cancer tissue samples. Recently developed applications include quantification of protein expression in fixed archival tissue with an emphasis on oral cavity (head and neck squamous cell carcinoma—HNSCC) and breast cancer. Spectral count bioinformatics provides a non-labeling method for quantitative proteomics of formalin-fixed histologically-defined oral cavity cancer. Results indicate many proteins were differentially expressed in cells obtained by laser microdissection of normal, highly differentiated, moderately differentiated, and poorly differentiated HNSCC fixed tissue. Candidate protein biomarkers found to be differentially expressed in the process of HNSCC progression were confirmed and validated by immunohistochemistry on large panels of HNSCC tissue. In addition, we have developed and evaluated a method for direct detection and absolute quantification by selected reaction monitoring (SRM) of HER2 directly in formalin-fixed paraffin-embedded breast cancer tissue using a stable isotope standard peptide derived from HER2. Soluble protein extracts from a collection of breast cancer tissues known to express a range of HER2 were prepared using Liquid Tissue reagents, and quantitative levels were determined. Results demonstrate the ability to quantitate HER2 expression in Liquid Tissue extracts from fixed tissue sections that correlate with standard IHC and indicate the ability to quantify HER2 in immunohistochemical-negative cells. These cumulative results demonstrate development of technologies for quantitative proteomic analysis of proteins that can be applied to the vast worldwide formalin-fixed tissue archives.
