Clonal Hematopoiesis Associated with Adverse Outcomes Following Autologous Stem Cell Transplantation for Non-Hodgkin Lymphoma

Background

Clonal hematopoiesis of indeterminate potential (CHIP) is an age-related phenomenon characterized by the presence of somatic mutations in peripheral blood (PMIDs: 25426837, 25426838). Although CHIP was originally defined in healthy older adults without cytopenias, it can be found in other contexts as well. For example, one recent report described four patients with therapy-related myeloid neoplasm (TMN) arising after treatment for other cancers, all of which were driven by TP53 mutations that could be found at very low levels in samples drawn years before the development of TMN (PMID: 25487151). However, there has not yet been a more systematic study of CHIP in this type of context.

In this study, we sought to understand how CHIP behaves and influences outcomes in the context of autologous stem cell transplantation (ASCT), arguably the most extreme selective pressure that can be studied in the context of native hematopoiesis. We hypothesized that in patients with Non-Hodgkin Lymphoma (NHL) undergoing ASCT, the presence of CHIP at the time of transplantation would be associated with an increased risk of TMN and other adverse outcomes.

Methods

We analyzed exome sequencing data from 10 patients with TMN after ASCT (City of Hope Cancer Center, Duarte, CA), and performed targeted sequencing of 116 genes on banked, mobilized peripheral blood from an additional 401 patients with NHL who underwent ASCT (Dana Farber Cancer Institute, Boston, MA), to determine whether there is a clonal connection between CHIP at the time of ASCT and subsequent TMN, and to determine whether the presence of CHIP at the time of ASCT influences subsequent outcomes.

Results

In 7 of 10 TMN patients for whom we analyzed exome sequencing data, mutations present at the time of TMN were also detectable in the pre-ASCT sample. PPM1D, a key mediator of the DNA damage pathway, was mutated in 2 patients, as was TP53 (2 patients), TET2 (2 patients) and PRPF8 (1 patient). In our larger cohort of 401 unselected ASCT patients, CHIP was common (121 patients, 30.2%) and was associated with older age but not with other demographic or treatment-related factors. PPM1D was the most commonly mutated gene (54 mutations in 48 patients).

In the ASCT cohort of 401 patients, 18 patients developed TMN. The presence of CHIP at the time of ASCT significantly increased this risk: the 10-year cumulative incidence of TMN, with death and allogeneic transplant as competing risks, was 12.4% for patients with CHIP, compared to 3.5% for patients without CHIP (P=0.002, Figure 1A). Moreover, the presence of CHIP at the time of ASCT conferred significant risks beyond TMN alone, as patients with CHIP had significantly inferior overall survival compared to patients without CHIP (10-year OS 30.6% versus 60.9%, P=0.0003, Figure 1B). This difference was driven primarily by late mortality and not by an increased risk of relapse or by the difference in rate of TMN. Although other variables were associated with OS in univariate analysis, multivariate analysis in a Cox proportional hazards model showed that only older age (60 or above), aggressive lymphoma, and presence of CHIP were significantly associated with survival.

Conclusion

We show that CHIP at the time of ASCT for NHL is common and is associated with an increased risk of TMN and decreased overall survival independent of the TMN risk. These results have substantial clinical and translational implications. They suggest the need to specifically study the connection between CHIP and lymphoma more deeply, which could be accomplished by assessing CHIP in patients with newly diagnosed lymphoma prior to the administration of any chemotherapy or mobilizing agents. They also suggest the need to consider alternative therapeutic approaches for patients with lymphoma and a high risk of TMN who are being considered for ASCT. Finally, they underscore the need to study clonal hematopoiesis in the context of treatment for other cancers to determine whether these results may be relevant to an even larger number of patients.

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