Gene expression microarray-based assay to determine tumor site of origin in a series of metastatic tumors to the ovary and peritoneal carcinomatosis of suspected gynecologic origin.

The origin of the primary tumor is sometimes difficult to determine in peritoneal and ovarian metastases. A series of 25 metastatic tumors to the ovary and 7 cases of peritoneal carcinomatosis of suspected gynecologic origin were collected. Total RNA was extracted from frozen tumor tissue and studied by the Tissue of Origin-Frozen test, a microarray-based gene expression test from Pathwork Diagnostics (Redwood City, CA). Independently, formalin-fixed, paraffin-embedded tumor tissue was subjected to pathologic analysis. Immunohistochemical stains included keratins 7 and 20, estrogen and progesterone receptors, CDX2, villin, CEA, WT-1, TTF-1, mammoglobin, GCDF-15, and CD31. Clinical data were considered as gold standard, and after clinicopathologic evaluation, the tissue of origin was found in 29 cases. The Tissue of Origin-Frozen test correctly identified the ovary as site of origin in 7 of 7 peritoneal carcinomatosis cases, whereas immunohistochemical stains only allowed appropriate recognition in 5. In addition, the Tissue of Origin-Frozen test identified correctly the site of origin in 18 of the 22 metastatic tumors to the ovary with known origin. In the remaining 4 tumors, the correct origin was the second option in 2 cases and was not determined in the other 2. Immunohistochemistry correctly identified the site of origin in 17 of these 22 ovarian metastases. A combination of Tissue of Origin-Frozen and immunohistochemistry correctly identified the site of origin in 19 of 22 ovarian metastases of known origin. Although conventional pathologic examination and immunohistochemistry are commonly used for assessing the tumor site of origin, Tissue of Origin testing can be useful in difficult cases.