Clonal relationship of synchronous head and neck cancer and esophageal cancer assessed by single nucleotide polymorphism-based loss of heterozygosity analysis

BACKGROUND: The prognoses of head and neck squamous cell carcinoma (HNSCC) and esophageal squamous cell carcinoma (ESCC) are poor, especially when both tumors occur at the same time. We examined the clonal relatedness of HNSCCs with synchronous ESCCs to confirm whether the second tumors were metastasis or separate second primary malignancies (SPMs) using loss of heterozygosity (LOH) analysis. METHODS: Twenty-one pairs of formalin-fixed paraffin-embedded tissue from HNSCC patients with synchronous esophageal cancer were analyzed by single nucleotide polymorphism (SNP) array using the Illumina HumanCytoSNP FFPE-12 BeadChip (San Diego, CA), which contains approximately 300,000 probes. LOH was identified using Nexus Copy Number software (El Segundo, CA). RESULTS: Comparing the LOH pattern between HNSCC and paired ESCC, we found that 20 out of 21 paired tissues had a high number of discordant LOHs (LOH identified solely in the primary HNSCC but not in synchronous ESCC at the same genomic location) and a low number of concordant LOHs (LOH at the same genomic location in both HNSCC and ESCC). Only one case fell into the undetermined category. Therefore, these 20 ESCCs were classified as SPMs or second field tumors (SFTs). Moreover, the HNSCC patients with molecularly confirmed esophageal SPM had significantly poorer survival than the other patients. CONCLUSIONS: We propose the use of a genome-wide SNP array as a tool to differentiate metastatic tumors from SPM/SFT. The SNP array offers genome-wide LOH information that earlier microsatellite analysis studies lack. The ability to accurately identify SPM should contribute to a better treatment plan and follow-up care of these patients.