Estimation of expected survival time using gene expression profiling for tumor site origin.

Abstract

10584 Background: Expected survival is an important factor in treatment selection and patient decision making. Gene expression profiling for tissue of origin (GEP TOO) can be used to classify metastatic and poorly-differentiated tumors according to the most likely primary site for difficult-to-diagnose tumors. The Pathwork Tissue of Origin Test, (Redwood City, CA) generates Similarity Scores (SS), one for each of the 15 tissues on the Tissue of Origin Test Panel and sum to 100. The highest SS has been validated as the most likely tissue of origin in a large validation study (Pillai et al. 2010). This abstract reports the relationship between the highest SS for a sample and patient survival. Methods: Two cohorts were analyzed in IRB-approved studies. Cohort 1 consisted of 45 patients with carcinoma of unknown primary treated empirically with therapy for carcinoma of unknown primary with known outcome data including survival. Cohort 2 consisted of 107 patients receiving the TOO test in routine clinical practice and included in a decision impact registry study. The relationship between the highest SS generated by the TOO test was examined using parametric (Gamma) and non-parametric (Cox Proportional Hazards) regression models with covariates of age, gender and median survival of the cancer type indicated. Logrank tests were performed to compare survival in patients with SS above or below 50 in each cohort. Results: The highest SS generated by the TOO Test was strongly and positively correlated with patient survival in both Cohort 1 (p = 0.0093, Cox PH) and in Cohort 2 (p=0.0045, Gamma). In Cohort 1, survival for patients with a SS < 50 was 5.9 mos and for patients with a SS ≥ 50 was 9.7 mos (p=0.03, logrank). In Cohort 2, survival for patients with a SS < 50 was 10.6 mos and 22.6 mos for patients with a SS ≥ 50 (p=0.0073, logrank). Conclusions: The Similarity Scores generated by GEP TOO Test have been validated as an aid to diagnosis for difficult-to-diagnose malignancies. Two independent studies of this GEP TOO Test demonstrated a strong positive relationship between the highest SS and survival. This has the potential to expand the clinical utility of this test beyond diagnosis to include prognosis. Further studies to examine this question are underway.