Metastasis-associated mutations in clear cell renal cell carcinoma.

600 Background: Over 30% of patients with clear cell renal cell carcinoma (ccRCC) exhibit metastasis at the time of diagnosis and exhibit poor outcome. About 20-50% of patients with localized disease eventually develop metastasis after nephrectomy. The goal of the current study was to identify target gene mutations associated with ccRCC metastasis. Methods: In this IRB approved study, genomic DNA from 128 ccRCC resected specimens (128 unique patients) were profiled using a custom targeted next-generation sequencing (NGS) panel comprising 70 frequently mutated genes and prognostic SNPs in renal cancer. The specimen cohort consisted of 78 primary (29 stage I-III, 30 stage IV, 19 unknown) and 50 metastatic (10 lung, 9 bone, 25 other sites, 6 unknown) lesions. Following hybrid capture, sequencing was performed (MiSeq, Illumina) and variants identified using CLCbio (Qiagen). Chi-square test was used to test for significance. Results: The median specimen had 4 non-synonymous mutations (123/128 samples had at least one mutation). 66 genes showed a non-synonymous mutation in at least one specimen. There was no significant difference between total mutation count between primary and metastatic specimens (Mann-Whitney test). TSC1 mutation was significantly enriched in metastatic (8/50) compared with primary lesions (3/78). No TSC1 mutation was found in the 29 localized (stage I-III) primary lesions. Interestingly, TSC1 maps to 9q34 and our prior copy number studies indicated that loss of 9q is also enriched in metastatic lesions. Of the 11 specimens bearing TSC1 mutation in this cohort, 5 also had loss of 9q. In 44 specimens with known sites of resection, SETD2 and TSC1 mutations were not found in metastases to the lung but found in 30-40% of lesions at other sites, KDM5C and TSC1 mutations were not found in metastases to the bone while 25-30% of lesions at other sites exhibited these mutations. Due to the limited sample size, significance could not be determined for these associations. Conclusions: Preliminary results of this study implicated TSC1 in the metastasis of ccRCC. Since TSC1 mutation is known to confer sensitivity to mTOR inhibitors, our initial finding of absence of TSC1 mutation in lung and bone sites of metastasis may have therapeutic implications.