Incidence of mutated DNA damage response pathway and clinically actionable alterations in Chinese patients with unknown primary tumor revealed by comprehensive genomic profiling.

Abstract

e13523 Background: Carcinoma of unknown primary(CUP) is a clinically aggressive disorder with early tumor dissemination. Without drugs specifically approved for CUP, the outcome of standard chemotherapy is generally poor. Identifying molecular traits of CUP can be beneficial not only for better therapy approach but also potentially for all patients with metastatic dissemination. Methods: From January 2015 to July 2019, 36 unique cases were diagnosed as CUP. DNA was extracted with formalin-fixed paraffin-embedded specimens(FFPEs) or plasma samples and sequenced with 400+ gene panels. Results: In this cohort, identified sites of tumor dissemination included lymph node(36%), bone(19%), liver(8%), lung(5%), gut(5%). More than half of patients were male(65%) with a median age of 62 years old(range:42-82). 83% of CUP patients harboured at least one altered DNA damage repair(DDR) gene including TP53(74%), ATM(19%), ARID1A(11%), ATR(11%). Patients with altered homologous recombination repair (HRR) pathway(42%) showed significantly increased tumor mutational burden(TMB) compared to patients with intact HRR(p = 0.025). MYC gene displayed the most copy number variation (gain, 22%) followed by CDKN2A(loss, 15%) and ZNF217(gain, 15%). Clinically actionable mutations were identified in ten patients including KRAS G12C(3), PIK3CA E545K(2), PIK3CA E542K(1), BRAF V600L(1), EGFR L861Q(1), EML4- ALK(1), ALK L1196M(1). One SCC patient with lymph node metastasis had a PIK3CA mutation E545K and a resistant ALK mutation L1196M without prior ALK TKI treatment, suggesting this patient might benefit from PI3K inhibitors. Unfortunately, He progressed on paclitaxel and cisplatin and died in 2019. The other ADC patient with lymph node metastasis achieved SD on pemetrexed disodium and oxaliplatin. He harboured a KRAS G12C mutation (allele frequency 77.75%), indicating target therapy with KRAS inhibitor might be a better treatment option. Conclusions: Majority of CUP patients showed impaired DDR pathway. TMB of CUP patients with altered HRR pathway is significantly higher than ones with intact HRR. Comprehensive genomic profiling revealed the potentiality of target therapy in CUP patients with clinically actionable mutations.