Unknown primary cancer (UPC): Accuracy of tissue of origin prediction by molecular profiling

Abstract

11070 Background: Molecular profiling may be useful to identify the primary site and direct therapy for patients (pts) with UPC. Since most UPC pts never have a primary site identified, the accuracy of molecular profiling diagnoses are difficult to verify. We identified a group of UPC pts who had a primary site subsequently identified during their clinical course, and performed a 92-gene real time polymerase chain reaction (RT-PCR) assay (Arch Pathol Lab Med 130:465, 2006) on tissue from the initial diagnostic biopsy. We then compared the RT-PCR diagnosis with the subsequent clinical diagnosis. Methods: 38 of 501 UPC pts (7%) seen between 2000 and 2008 had their primary tumor subsequently identified during life. 24 of the 38 pts had tissue biopsies (excluding FNA cytology) and are the subject of this study. The RT-PCR assay was performed on unstained slides from the formalin-fixed, paraffin-embedded (FFPE) initial diagnostic biopsy, and the assay predictions were compared to the actual primary sites (found later). No clinical or pathologic data (other than sex, biopsy site, and 1 H&E stained slide) were used in the prediction of the primary site. Results: 16 of 24 assays were successful (8 had no tumor or RNA in the material). 11 of 16 predictions of the site of origin (68%) were correct, corresponding to the actual primary sites found 3–58 months (median 8.5 months) after the initial diagnosis of UPC. Primary sites correctly identified included breast 2, ovary/peritoneal 4, NSCLC 1, colorectal 2, gastric 1, melanoma 1. 3 predictions were inaccurate (colorectal, testicular, sarcoma) in patients with gastroesophageal, pancreas and NSCLC, respectively. 2 assays were unclassifiable. Conclusions: RT-PCR performed on FFPE initial diagnostic tissue was accurate in predicting the primary site of origin in 11 of 16 pts with UPC who eventually had their primary site identified clinically. These data provide a direct validation of the reliability of this RT-PCR assay in predicting the primary site in pts with UPC. When used in concert with clinical features and IHC stains, molecular profiling may provide the basis for more successful site-directed therapy for many of these pts. Prospective studies of RT-PCR in UPC are ongoing. [Table: see text]