Abstract 5361: Isolation and genetic characterization of circulating tumor cells from cancer of unknown primary
Authors: Porcellini Elisa , Gelsomino Francesco , Laprovitera Noemi , Riefolo Mattia , Garonzi Marianna , Tononi Paola , Fontana Francesca , D'Errico Antonia , Pantaleo Maria , Manaresi Nicolò , Ardizzoni Andrea , Ferracin Manuela 
Published: September 2020

Background Cancer of unknown primary (CUP) is a heterogeneous group of metastatic cancers whose primary site cannot be determined after standard clinical and pathological evaluation. CUP patients are generally treated with empirical chemotherapy and have poor prognosis. As reported in recent studies, CUPs present an average of 4 genetic alterations per tumor and these genetic alterations can be detected in circulating tumor DNA (Kato 2017). Thus, a potential improvement in CUP outcomes could derive from targeted therapies directed toward actionable mutations, and Circulating tumor cells (CTCs) can provide valuable information. Here, we describe a case of a 51-yr-old Caucasian female (Pt#71) with metastatic CUP. CTCs were detectable in her blood and analyzed for genetic alterations.

Methods Using CellSearch and DEPArray NxT, n=3 CTCs and n=1 leukocyte as a control were isolated from patient's peripheral blood. Single-cell whole genome amplification was obtained with Ampli1 WGA Kit and libraries were generated with Ampli1 OncoSeek Panel and Ampli1 LowPass kits. In parallel, formalin-fixed paraffin embedded (FFPE) tissue derived from a lymph node biopsy was analyzed with two different methods. One curl was sent for comprehensive genomic profile to FoundationOne assay testing (Roche). From another curl, DNA was extracted and directly processed with DEPArray LibPrep and DEPArray OncoSeek Panel kits. After sequencing on Illumina MiSeq platform, raw data were analyzed on MSBiosuite platform (Menarini Silicon Biosystems).

Results CTCs genome-wide characterization allowed the detection of sub-chromosomal losses, including a LOH region comprising the APC gene, and patterns of extensive gains. Moreover, amplification signals were detected in correspondence of FGFR2 and CCNE1 genes. Targeted sequencing on both CTCs and bulk tumor DNA confirmed the FGFR2 amplification in all the samples and detected a somatic variant in APC gene (APC:p.T1556Nfs*3). FoundationOne assay on FFPE biopsy reported the same amplification on FGFR2 and CCNE1 genes, along with a somatic variant in ARID1A gene (ARID1A:p.R1276*), a gene not present in the OncoSeek Panel. On the other hand, APC somatic variant was not identified by FoundationOne, probably due to contamination by normal cells and/or tumor heterogeneity.

Conclusions The comprehensive genomic profile of tumor FFPE tissue and CTCs was highly overlapping and allowed the characterization of genetic alterations in this CUP case, revealing potentially actionable mutations and copy number alterations. The advantage of isolating and analyzing single CTCs is clearly shown by the non-invasive procedure combined with a precise detection of druggable alterations due to cell purity.

Citation Format: Elisa Porcellini, Francesco Gelsomino, Noemi Laprovitera, Mattia Riefolo, Marianna Garonzi, Paola Tononi, Francesca Fontana, Antonia D'Errico, Maria Pantaleo, Nicolò Manaresi, Andrea Ardizzoni, Manuela Ferracin. Isolation and genetic characterization of circulating tumor cells from cancer of unknown primary [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 5361.