Comprehensive genomic profiling of squamous cell carcinoma of unknown primary presenting with liver metastases.

Abstract

755 Background: Carcinomas of unknown primary (CUPs) are comprised of metastatic cancers for which a primary tumor of origin cannot be identified despite a full diagnostic workup. They frequently present with liver metastases, which portend a poor prognosis. Strategies employing comprehensive genomic profiling (CGP) to identify targeted treatments for CUPs have shown potential. Despite this, the molecular landscape of squamous cell carcinomas of unknown primary (SCCUPs) remains poorly defined. This study describes the results of CGP testing in patients with SCCUPs identified in the Foundation Medicine, Inc. database, with a focus on those with liver involvement. Methods: Cases of SCCUPs with FoundationOne CDx (F1CDx) assay results were identified based on a reported diagnosis of CUP and the presence of SCC histology. Cases then underwent central pathologist review and were excluded if a known primary site could be determined based on histology and disease location. Cases with liver involvement were selected based on the site of tissue biopsy. Genomic analyses of identified cases were assessed using the FoundationCORE database. Results: Sixty-nine cases of SCCUP presenting with liver involvement were identified. Alterations were observed in 102 of 324 (31.5%) genes evaluated by the F1CDx assay in at least 1 patient. The most frequently altered genes were TP53 (66.7%) , CDKN2A (33.3%) , CDKN2B (23.2%) , KRAS (21.7%; 0% G12C) , PIK3CA (18.8%), NFE2L2 (11.6%), SOX2 (11.6%), M2M2 (10.1%), and MTAP (10.1%). No patients had microsatellite instability-high disease, only 6 (8.7%) patients had a tumor mutational burden (TMB) ≥ 10, and 11 (15.9%) patients had evidence of HPV infection. Among 33 patients with available PDL-1 testing results, 7 (21.2%) had high-positive expression. An additional 374 cases of SCCUP were identified with involvement outside of the liver. Compared to these cases, patients presenting with liver involvement had less genomic alterations per tumor (5.10 vs 6.71, p=0.005), and were less likely to have TMB ≥ 10 (8.7% vs 38.0%; odds ratio [OR] 0.16, p<0.001). KRAS mutations were observed in 21.7% of those presenting with liver metastases compared to 8.3% of other SCCUP patients (OR 3.07, p=0.07). Conclusions: SCCUPs presenting with liver metastases had reduced numbers of genomic alterations and decreased TMB compared to other SCCUPs, suggesting these tumors may be less likely to respond to immunotherapy. Despite this, 36.2% of these patients had at least one alteration that could potentially guide targeted treatment decisions including entry into biomarker-driven clinical trials. Interestingly, there was a trend toward increased KRAS alterations in those with liver metastases. To our knowledge, this is the first report that describes the genomic landscape of SCCUPs presenting with liver metastases.