Abstract 5432: Cancer of unknown primary site-of-origin: An enigma ready to be miR-solved

Background Cancer of Unknown Primary is a rare syndrome of metastatic cancers for which the primary site cannot be recognized after detailed physical examinations, blood analyses, imaging and immunohistochemical (IHC) testing. CUPs make up 3-5% of newly diagnosed cancers worldwide and represent an important diagnostic and clinical problem. Treatment failure to empirical chemotherapy is common, resulting in progressive disease and poor prognosis. We and others proposed that a molecular inference of the tissue of origin could be feasible for most CUP tumors (Ferracin et al. J Pathol, 2011), thus giving access to more effective therapeutic agents and potentially extending CUP patient life-expectancy. Methods We optimized a cancer-type classifier based on microRNA (miRNA) expression for the prediction of CUP primary tumor site (Laprovitera et al., Front Oncol. 2018). Specifically, we designed a molecular assay to quantify the absolute copy number of 89 miRNAs in formalin-fixed paraffin-embedded (FFPE) samples using EvaGreen-based Droplet Digital PCR (BioRad). We tested 153 samples from three groups: primary tumors (N=95), metastases of known origin (N=10) and cancers of unknown origin (N=48). CUP diagnosis was obtained after a detailed histo-pathological investigation as per CUP diagnostic guidelines (NCCN occult primary v.2-2019 and ESMO guidelines). The study was approved by the local ethical committee. Results We investigated a pre-determined set of 89 miRNAs to infer the site-of origin of metastatic cancers of unknown or uncertain primary. Primary tumors from 16 different sites (lung, pancreas, liver, bile duct, kidney, bowel, testis, ovary, endometrium, stomach, bladder, breast, prostate, melanoma, gastrointestinal neuroendocrine, head and neck) were tested for absolute miRNA expression and used to train our classifier (Tibshirani et al. PNAS, 2002). We used the metastases of known origin as a test-set for our molecular prediction. We applied the shrunken centroids approach as predictive algorithm to obtain the most probable CUP site(s)-of- origin. Our results were judged against the hypothesized primary site suggested by standard diagnostic workup and pathological assessment. The molecular test was successfully applied to all CUP samples and provided a site-of-origin identification (with a probability > 50%) for all samples, potentially within a one-week time frame from sample inclusion. Conclusions Our study demonstrated that miRNA expression profiling in CUP samples have the potential to be employed in a clinical setting. Our molecular analysis can be performed on-request, concomitantly with the standard diagnostic workup and in association with genetic profiling, to offer valuable indication about the possible primary site thereby supporting treatment decisions. This work was supported by grants from the Italian Association for Cancer Research (AIRC) to MF (IG 18464). Citation Format: Noemi Laprovitera, Elisa Porcellini, Mattia Riefolo, Elisabetta Broseghini, Ingrid Garajova, Silvia Sabbioni, Martin Pichler, Andrea Ardizzoni, Antonia D'Errico, Manuela Ferracin. Cancer of unknown primary site-of-origin: An enigma ready to be miR-solved [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5432.