This will be a multi-center prospective study of up to 350 patients, each having both pre-treatment (prior to chemoradiation) unstained sections on charged slides from the FFPE block that was used for diagnosis of rectal or anal cancer and sections of unstained, post-surgical, resected tissue (pathologic confirmation of treatment response based upon endoscopy or ultrasound can be accepted in place of post-surgical resected tissue). Per the CLIA-compliant SOPs (Appendix A), one slide will be stained with H&E to define the area of tumor within the tissue, and the remaining slides will be used for immunohistochemical (IHC) detection of the biomarkers described above to assess the performance of the proprietary IHC assay. Any remaining slides not used for IHC staining will be used for a parallel gene expression discovery effort using TaqMan high throughput RT-PCR analysis (Appendix B, Sub-study 1).