Circulating Tumor DNA Predicts Time to First Treatment in Previously Untreated Follicular Lymphoma: Analysis from a Prospective Clonal Evolution Study
Authors: Lakhotia Rahul , Pittaluga Stefania , Phelan James D. , Graeter Allison , Melani Christopher , Gordon Max J , Muppidi Jagan R. , Ng Sam Y. , Berg Sumaya , Evans Sarah , Pradhan Amynah , Tadese Atekelt , Morrison Candis , Bryant Bonita , Yang Yandan , Davies-Hill Theresa , Lindenberg Liza , Ahlman Mark , Mena Esther , Bergvall Ethan , Micheletti Nick , Yee Laura M , Jacob Allison P. , Gallucci Monica , Simmons Heidi , Bagaev Alexander , Meerson Mark , Postovalova Ekaterina , Kudryashova Olga , Kotlov Nikita , Fowler Nathan H. , Jaffe Elaine S. , Staudt Louis M. , Wilson Wyndham H. , Roschewski Mark 
Published: December 2024

Background:Follicular lymphoma (FL) shows marked heterogeneity in clinical course including spontaneous regression and histologic transformation (HT). Watchful waiting (W&W) is routinely employed, but monitoring is not standardized. A subset of pts require treatment early after diagnosis, but biologic basis is unclear. Improved classifiers and monitoring tools are needed. Circulating tumor DNA (ctDNA) is a highly tumor-specific biomarker that is prognostic in aggressive B-cell lymphomas. We previously showed that ctDNA in plasma can be identified in &gt;90% FL pts with next-generation sequencing of Ig heavy- and light-chain loci. Here, we present updated results from serial ctDNA monitoring of pts on a prospective clinical trial [NCT03190928].

Methods:

Adult pts with grade 1-3A FL were eligible if evaluable disease, no HT, and no prior systemic therapy. Pts underwent W&W until they met uniform protocol-defined treatment criteria and then monitored until 2nd line therapy. Baseline testing included plasma, CT and PET, and biopsy. Clinic visits were every 4m for 2y, every 6m in years 3-5, then annually with CT scans every other clinic visit. PET scans were repeated at 2y, or at suspected disease progression. Cell-stabilizing tubes (plasma) and PBMCs were drawn at each visit. Analysis of ctDNA was performed using the research version of clonoSEQ blinded to clinical outcomes. The primary endpoint was progression requiring treatment within 2 years of enrollment. Pts who required treatment in first 2 years were labeled early progressors and those without treatment were labeled non-progressors.

Results:

78 pts enrolled between July 2017 and Aug 2021, of which 77 had baseline plasma samples. Of 58 pts with available FFPE tumor biopsies, all (100%) had ≥1 dominant clonotype(s) identified from tumor. Of 19 pts without FFPE, ≥1 dominant clonotype was identified from plasma in 7 (37%). These 65 pts with trackable clonotype(s) comprised the study population. Median age of the study population was 57y (range 24-84), including 12 (18%) low-risk, 25 (39%) intermediate-risk, and 28 (43%) high-risk by FLIPI. Baseline ctDNA was detectable in 60 (92%) pts with median (interquartile range [IQR]) level of 34 (6-114) lymphoma molecules per mL. Four (80%) pts with undetectable ctDNA at baseline had stage 1-2 disease. Baseline ctDNA levels correlated with both FLIPI (p&lt;0.01) and total metabolic tumor volume (TMTV) on PET (p&lt;0.001).

Three pts were unevaluable for progression at 2y due to non-progression events including a second malignancy, sudden death, and hemolytic anemia requiring rituximab. Thirty-three (53%) pts were early progressors and 29 (47%) were non-progressors at 2y. Median time to treatment (TTT) was 20m (95% CI, 10-68). Early progressors had median (IQR) baseline ctDNA level of 38.2 (13-189.4) compared to 18.7 (1.2-56.8) lymphoma molecules per mL for non-progressors. Pts with &gt;median baseline ctDNA levels had median TTT of 9.7m (95% CI, 2.8-NE) compared to 37m (95% CI, 17-NE) for pts with &lt;median ctDNA (p=0.06). All 5 pts with undetectable baseline ctDNA remained treatment free after median 5.4y of follow-up.

Median (IQR) baseline TMTV was 138 (39-388) cm3. Pts with &gt;median baseline TMTV had median TTT of 5.3m (95% CI, 2.1-28) compared to 54m (95% CI, 26-NE) for pts with &lt;median TMTV (p&lt;0.001). Serial ctDNA samples were available for 37 pts. Rising ctDNA levels were observed in 10 (83%) of 12 pts prior to or at the time of treatment. Fluctuating ctDNA patterns were observed in 25 pts without progression which corresponded to changes on serial CTs.

Ten (15%) pts had HT. Neither baseline ctDNA levels (p=0.85) nor TMTV (p=0.65) were associated with increased risk of subsequent HT. Twenty-three (39%) pts had spontaneous regression of tumor lesions by ≥25% on CT. Lower baseline ctDNA levels (p=0.02) and TMTV (p&lt;0.01) were associated with subsequent spontaneous regression. Twenty pts with spontaneous regression had serial samples and 13 (65%) had decrease in ctDNA levels corresponding to CTs.

Conclusions:

Circulating tumor DNA is detectable in baseline plasma of &gt;90% pts with untreated FL. Quantitative ctDNA levels correlate with both FLIPI and TMTV and are associated with earlier need for treatment. Serial ctDNA monitoring shows fluctuating levels that correlate with tumor burden on CT which provides a non-invasive method to monitor disease. Baseline ctDNA levels and TMTV do not predict future histologic transformation.