FDA Clears Test that Helps Identify Cancer Type in Tumor Sample

Abstract

The US Food and Drug Administration (FDA) on July 31, 2008, cleared for marketing a test that can help health care professionals to determine what type of cancer cells are present in a malignant tumor. The Pathwork Tissue of Origin test compares the genetic material of a patient's tumor with genetic information on malignant tumor types stored in a database. The test uses microarray technology to analyze thousands of pieces of genetic material at 1 time and considers 15 common types of malignancy, including bladder, breast, and colorectal tumors. “The clearance of the Pathwork test is another step in the continued integration of molecular-based medicine into standard practice,” said Daniel Schultz, MD, director of the FDA's Center for Devices and Radiological Health, which oversees medical diagnostics. “In the past, scientists have classified different types of cancers based on the organs in which the tumors develop. With the help of microarray technology, they will be able to classify these types of cancers in a standardized non–reader-dependent manner based on the patterns of gene activity in the tumor cells.” The Pathwork Tissue of Origin test is the second in vitro diagnostic multivariate index assay (IVDMIA) device to be cleared by the FDA. In July 2007, the FDA issued a draft guidance document to address premarket pathways and postmarket requirements for IVDMIAs. These tests combine the values of multiple variables to yield a single, patient-specific result. Microarray technology can simultaneously measure gene expression levels of large numbers of genes. Small DNA fragments are placed or arrayed on a slide and then RNA, which has been extracted from the tumor tissue and labeled with a fluorescent marker, is spread over this “microarray.” Because RNA binds to its complementary DNA strand, the level of binding that occurs indicates how active the gene being evaluated is. This is determined by placing the array under a scanning microscope and measuring the intensity of the fluorescent light at each RNA–DNA site on the array. Pathwork's proprietary software converts the scanned image data to gene expression measurements. The gene expression patterns are then compared with known gene expression patterns in the database that correspond to different tumor types. The Pathwork Tissue of Origin test has been demonstrated to provide patterns that confirm the existing tissue of origin of the 15 common tumor types using standard clinical and pathologic information. The accuracy of this test is similar to that achieved by expert pathologists using current standards of practice. PathChip, the gene expression array used in the Pathwork Tissue of Origin test, is custom-designed for Pathwork Diagnostics of Sunnyvale, California, by Affymetrix Inc., of Santa Clara, California. PathChip is the first custom Affymetrix gene expression array to be cleared for diagnostic use.