Abstract 4529: Prognostic implications of TSPO in human colorectal cancer

Translocator protein (TSPO), previously referred to as peripheral benzodiazepine receptor, is an 18kDa outer mitochondrial membrane protein involved in a number of cellular processes including steroid synthesis, cholesterol metabolism, proliferation, and apoptosis. Elevated TSPO expression has been linked with disease progression, diminished survival, and aggressiveness in a number of cancers. Studies conducted in our laboratory have demonstrated that positron emission tomography (PET) imaging with TSPO targeted probes can be used to non-invasively quantify TSPO levels in tumors. These imaging studies suggest that TSPO ligand PET may be a valuable clinical cancer imaging biomarker. In the current studies, TSPO expression in human colon cancer and paired liver metastases was evaluated using tissue microarrays. These arrays were constructed using 99 primary colon cancers and 95 matched primary colon cancers and liver metastases from Vanderbilt patients with known clinical outcomes. Among these, we found that nearly 2/3 of the colon cancers were positive for TSPO expression (64%). Similar to previous studies in other organ sites, elevated TSPO expression was significantly associated with higher tumor grade in the Vanderbilt cohort of CRC patients. Among patients with grade 2 or grade 3 tumors, an individual with elevated TSPO expression was 3 times more likely to have a grade 3 tumor than a grade 2 tumor. In comparing matched primary colon cancers and associated liver metastases, we found a strong concordance between TSPO levels and localization across matched specimens. No correlation was observed between TSPO expression and Ki67 or pEGFR levels suggesting the potentially unique information provided by the measurement of TSPO levels. In conclusion, clinically relevant prognostic information can be obtained by the measurement of TSPO expression in colorectal cancer. Thus, TSPO targeted PET may be a promising-non invasive biomarker in this setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4529. doi:1538-7445.AM2012-4529