Abstract LB-B02: Detection of Clonal Hematopoiesis of Indeterminate Potential in Solid Tumors: Implications for Interpretation of Molecular Testing
Authors: Severson Eric A. A. , Riedlinger Gregory M. , Goldfinger Mendel , Connelly Caitlin , Ramkissoon Shakti , Frampton Garrett , Ross Jeffrey , Miller Vincent , Vergilio Jo-Anne , Elvin Julia , Hadigol Mohammad , Hirshfield Kim M. , Rodriguez-Rodriguez Lorna , Ganesan Shridar , Khiabanian Hossein 
Published: August 2018

Clonal hematopoiesis of indeterminate potential (CHIP) is caused by the expansion of hematopoietic stem cells that harbor oncogenic mutations. CHIP is associated with older age and increased mortality, and has been detected in a substantial percentage of the normal peripheral blood of cancer patients. Here, we hypothesize that CHIP may also be detected in solid tumor sequencing assays due to the presence of admixed hematopoietic cells; some mutations present in these data, especially those present at lower mutation allele frequency (MAF) relative to the tumor major clone, may signal the presence of CHIP rather than alterations in the solid tumor, and directly impact diagnosis, treatment, and patient prognosis.

Comprehensive genomic profiling (CGP), even without matched normal DNA, provides an unbiased view of both heterogeneous solid tumor cells and admixed non-tumor populations. CGP using the FoundationOne® and FoundationOne®Heme platforms was used to profile 97,670 solid tumors, with 257 shared genes interrogated via DNA-seq by both assays. These tumors were categorized into 23 cancer types. Logistic regression was used to evaluate the relationship between genomic alterations and patient age. The probability that each mutation’s MAF was significantly less than expected from tumor purity was calculated. CHIP-associated mutations were defined as those in the NCCN guidelines for Myelodysplastic Syndrome or previously detected CHIP in healthy individuals.

CHIP-associated alterations should correlate with increasing age regardless of tumor type. Therefore, the log odds ratio of alteration rate for each disease group and gene combination before and after age 60 was calculated. After correction for multiple

hypotheses, only DNMT3A, TET2, SF3B1, and ASXL1 had significantly more alterations after age 60 across all disease groups (p &lt;0.05). Concordantly, the rates of mutations within DNMT3A, TET2, SF3B1, and ASXL1 were strongly correlated with increasing patient age (DNMT3A p = 9.1E-75;TET2 p = 1.8E-109; SF3B1 p = 3.4E-47; ASXL1 p = 1.9E-41). Moreover, mutations in these genes were detected at decreased MAFs in patients older than 60 years (DNMT3A p &lt;1.3E-6; TET2 p &lt;3.1E-15; ASXL1 p &lt;6.1E-7; SF3B1 p &lt;2.7E-13).

To validate that these mutations existed in non-tumor elements, CGP of 1,636 solid tumors treated at Rutgers were analyzed; 36 patients had TET2 and DNMT3A mutations at MAFs significantly below the expected (p &lt;0.05). The median age of these patients was 68 years; 53% of them had a history of smoking, and 58% had chemotherapy and/or radiation prior to CGP. Matched peripheral blood samples were available for 13 patients; microdissected lymphocytes from a lymph node biopsy without histologic evidence of tumor were available for another patient. When these hematopoietic samples were sequenced, 11 out of 14 (79%) had the same TET2 or DNMT3A mutation found in the solid tumor. For the other three patients, the mutations were detected exclusively in microdissected tumor cells enriched from the original samples.

Overall, our analysis provides compelling evidence that when CHIP-associated mutations are observed in high-depth CGP of solid tumor samples at MAFs significantly different than expected, caution is necessary for appropriate patient management, and a hematologic workup should be considered in the appropriate clinical context.

Citation Format: Eric A. A. Severson, Gregory M. Riedlinger, Mendel Goldfinger, Caitlin Connelly, Shakti Ramkissoon, Garrett Frampton, Jeffrey Ross, Vincent Miller, Jo-Anne Vergilio, Julia Elvin, Mohammad Hadigol, Kim M. Hirshfield, Lorna Rodriguez-Rodriguez, Shridar Ganesan, Hossein Khiabanian. Detection of Clonal Hematopoiesis of Indeterminate Potential in Solid Tumors: Implications for Interpretation of Molecular Testing [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B02.