Previstage™ GCC Technical Information

Limitations of Traditional Staging

Traditional methods of examining lymph nodes (LNs) for metastases involve microscopically examining hematoxylin and eosin (H&E) stained 5µm sections of each LN. However, this method has two important limitations. From a sampling perspective, less than 1% of a node is often examined resulting in a significant chance of missing metastases.[3] Figure 1 illustrates two photomicrographs of sections taken through a lymph node at different levels. Section 1 shows the absence of visible metastases, while section 2, taken several sections lower through the same lymph node, reveals the presence of clear metastases. This example clearly shows the problem with traditional sampling.

2 H&E slides of the same colorectal cancer lymph node

Figure 1

Two photomicrographs of sections in the same lymph node, taken at different depths through the node. Section 1 shows the absence of metastases, while Section 2 clearly shows the presence of metastases. Slide source: Bernard Tetu, M.D., Centre Hospitalier Universitaire de Quebec, L’Hotel-Dieu de Quebec, Quebec, Canada

Additionally, studies have shown that the limit of detection for manual histologic examination of slides is about one malignant cell in a field of 200 normal cells.[3,4] Together, the limitations of inadequate sample review and low resolution for detecting metastases results in missed metastases and inaccurate staging.

More Sensitive Method of Detection

Molecular methods offer a more sensitive method of detecting occult metastases. As few as one metastatic cell in 10 million [6-7] normal cells can be detected as opposed to 1 in 200[2] by standard histopathology.[4] In addition, molecular methods interrogate a larger portion of the lymph node than traditional sectioning and therefore have the potential to identify occult metastases missed by histopathology.[1,5]

Several biomarkers have been introduced as possible markers for detecting occult metastases including CEA, CK-20, MAGE-A3, GalNAc-T, c-MET.[1,3,5,6] Although these have demonstrated some promise, none are specific only to colorectal cells, colorectal cancer or metastases, and therefore lack the specificity needed as a specific diagnostic marker for metastases.

Previstage™ GCC Colorectal Cancer Staging Test

A new molecular assay, the Previstage™ GCC Colorectal Cancer Staging Test overcomes problems with sampling errors, marker specificity and persistence of expression in CRC and metastases. Using ultrasensitive quantitative RT-PCR, the assay interrogates the patient’s lymph nodes to identify levels of GCC consistent with that found in LNs with histologically-confirmed, clinically significant metastases from stage III CRC patients. This unique methodology minimizes the sampling error inherent in traditional histopathological examination of lymph nodes and helps identify occult metastases that may result in a more accurate staging of the patient.

Key Points

  • Lymph node staging is the most important prognostic factor for CRC recurrence [1,2]
  • The number of lymph nodes to examine is debated, but generally a minimum of 12 is recommended [2]
  • Limitations on the volume of the lymph node examined as well as resolution of microscopy results in missed metastases [1]
  • Molecular methods of detecting metastases have been shown to be clinically significant for colorectal cancer prognosis [1,5,6]
  • Previstage™ GCC molecularly identifies occult metastases in the lymph node and provides a more accurate determination of the rectal or colon cancer stage than histopathology alone

References

  1. Iddings D, Ahmad A, Elashoff D, Bilchik A. The prognostic effect of micrometastases in previously staged lymph node negative (N0) colorectal carcinoma: a meta-analysis. Ann Surg Oncol 2006;13:1386-92.
  2. Compton CC, Fielding P, Burgart LJ, et al. Prognostic factors in colorectal cancer: College of American Pathologists Consensus Statement 1999. Arch Pathol Lab Med 2000;124:979-94.
  3. Frick GS, Pitari GM, Weinberg DS, Hyslop T, Schulz S, Waldman SA. Guanylyl Cyclase C: a molecular marker for staging and postoperative surveillance of patients with colorectal cancer. Expert Rev Mol Diagn 2005;5:701-13.
  4. Schulz S, Hyslop T, Haaf J, et al. A validated quantitative assay to detect occult micrometastases by reverse transcriptase polymerase chain reaction of Guanylyl Cyclase C in patients with colorectal cancer. Clin Canc Research 2006; 12:4545-52.
  5. Nicastri DG, Doucette JT, Godfrey TE, Hughes SJ. Is occult lymph node disease in colorectal cancer patients clinically significant? J Mol Diag 2007;9:563-71.
  6. Bilchik AJ, Hoon DSB, Saha S, et al. Prognostic impact of micrometastases in colon cancer: interim results of a prospective multicenter trial. Ann Surg 2007;246:568-77.
  7. Lucas KA, Pitari GM, Kazerounian S, et al. Guanylyl cyclases and signaling b y cyclic GMP. Pharmacol Rev 2000;52:375-413.
  8. Birbe R, Palazzo JP, Walters R, et al. Guanylyl Cyclase C is a marker of intestinal metaplasia, dysplasia, and adenocarcinoma of the gastrointestinal tract. Hum Pathol 2005;36(2):170-9.
  9. Cagir B, Gelmann A, Parks J, et al. Guanylyl Cyclase C messenger RNA is a biomarker for recurrent stage II colorectal cancer. Ann Intern Med 1999;131:805-12.