Paired matched normal sequencing to accurately identify somatic clonal hematopoiesis mutations (CHm) in solid tumor tissue and plasma specimens.

3051 Background: Clonal hematopoiesis (CH), characterized by the presence of somatic mutations in blood cells, can be found in cancer-related genes when sequencing tumor tissue or plasma samples. Inability to distinguish somatic, tumor-derived mutations from CHm can lead to inaccurate treatment decisions. In this prospective study, we confirmed potential CHm in solid tumors by sequencing and analysis of paired matched normal (PMN) specimens. Methods: We prospectively enrolled 56 patients diagnosed with advanced cancer, including lung (16), colorectal (13), breast (10), gastric (7), ovarian (2), pancreatic (2), liver (2), cervix (1), uterine (1), fallopian tube (1), and perihilar bile duct (1). Targeted next-generation sequencing using a 523 gene panel was performed on paired formalin-fixed paraffin-embedded (FFPE) and circulating tumor DNA (ctDNA) samples. Additionally, whole exome sequencing was performed on PMN buffy coat samples. Analysis of all three specimens was performed to classify somatic mutations as tumor-derived or CHm. Results: We identified 21 potential CHm within the FFPE and ctDNA samples of 13 patients (23.2% of the cohort) with lung (7), breast (2), liver (2), colorectal (1), and gastric (1) cancers. CHm were further confirmed when present in buffy coat samples. The VAF of CHm in FFPE and ctDNA samples exhibited a wide range, spanning from 0.85% to 38.4%, with 7 of those identified at <2% VAF. For these same aberrations, VAF in buffy coat samples ranged from 1.6% to 48%, with seven mutations exhibiting VAF levels <5%. Four of these CHm were classified as oncogenic or likely oncogenic. Four CHm, including an oncogenic TP53 mutation, were identified in the oldest patient (75 years old, lung cancer), while an oncogenic DNMT3A mutation was detected in the youngest patient (42 years old, breast cancer). Both had a 30-year history of smoking. Conclusions: Our findings identified somatic CHm in a substantial subset (23.2%) of solid tumors, with four identified as oncogenic or likely oncogenic mutations. The broad spectrum of VAFs for CHm suggests that using VAF as a cut-off to exclude likely CHm may be unreliable. The low VAF CHm found in matched normal specimens indicates low-pass sequencing may not detect critical CHm, even in paired analysis. The diverse age range of patients with CHm (42 to 75 years old) suggests that CHm are not restricted to older populations, and that additional factors, such as smoking history, may play a role. These findings underscore the importance of incorporating routine PMN buffy coat sequencing into clinical practice, to identify somatic CHm that can impact personalized cancer treatment strategies.