Evaluation of treatment responses to methotrexate and cyclophosphamide among T-LGL patients with and without Y640F and D661Y STAT3 mutations – a retrospective observational study Free

Introduction T-cell large granular lymphocytic leukemia (T-LGL) is a rare chronic lymphoproliferative disorder characterized by a clonal expansion of CD3+ T-lymphocytes and its association with autoimmune diseases such as rheumatoid arthritis (RA). The signal transducer and activator of transcription 3 (STAT3) pathway is a key pathway in T-LGL pathogenesis, with frequent gain of function mutations observed. Y640F and D661Y are the most common STAT3 mutations, accounting for ~60% of reported mutations. Despite its chronic and often indolent nature, treatment options for T-LGL are limited and can result in significant side effects. Data are mixed on whether or not STAT3 mutations are predictive of response to medications such as methotrexate (MTX) cyclophosphamide (CTX), which are the most commonly utilized medications to treat T-LGL. Given the rarity of T-LGL and its limited treatment options, a more comprehensive understanding of the impact of STAT3 mutations on treatment outcomes is urgently needed.

Methods Clinical characteristics and laboratory records were retrospectively reviewed for T-LGL patients who were evaluated at least once at a single academic center. All patients provided peripheral blood samples for STAT3 mutation analysis. Patients with multiple STAT3 mutations and patients with variant allele fractions less than 15% were excluded from this analysis. Patients were considered evaluable for response if they received at least 3 months of documented therapy and had clinical or laboratory follow up to confirm response. Complete response (CR) was defined as normalization of complete blood count (absolute neutrophil count (ANC) >1500/µL, absolute lymphocyte count <4000/µL, hemoglobin >11 g/dL, platelets >100,000/µL) on at least one laboratory assessment. Partial response (PR) was defined as hematological improvement without a CR (ANC >500/µL, increase in hemoglobin level by 1g/dL, or decreasing transfusion requirement). No response was defined as the lack of CR or PR. Data analysis was performed using GraphPad Prism 9.5.1 (GraphPad, San Diego, CA). Contingency analysis using chi-square or Fisher's exact test with two-tailed p values was performed to analyze the association between STAT3 mutation status and response to MTX or CTX. A p value of ≤0.05 was considered significant.

Results A total of 226 patients were analyzed, including 82 with STAT3 mutations (mutated) and 144 without STAT3 mutations (wild type, WT). Among mutated patients, 48 (58%) had Y640F mutation and 36 (42%) had D661Y mutation. Median follow up from time of T-LGL diagnosis to date of last clinic follow up was 6.8 years (range 0.4-28 years) for mutated patients and 5.6 years (range 0.2-23 years) for WT patients (p=0.34). Sex ratios were similar between mutated and WT patients (50% male vs 48% male). Comorbidities were balanced between groups (mean Charlson Comorbidity Index score of 2.5 versus 3.0 between mutated and WT patients, respectively). No difference in RA incidence was observed between mutated and WT patients (21% versus 27%, p=0.68). The most common treatment indications among mutated patients (n=81 who received at least 1 line of treatment) were neutropenia (51%), anemia (23%) and neutropenia with anemia (15%). The most common treatment indications among WT patients (n=137 who received at least 1 line of treatment) were neutropenia (52%), anemia (18%), and neutropenia with anemia (15%). Among evaluable patients, ORR to 1^st or 2^nd-line MTX regardless of treatment indication was 44% (51/116), 54% (21/39), and 50% (10/20) among WT, Y640F, and D661Y groups, respectively (p>0.05 for all comparisons). ORR to 1^st or 2^nd-line CTX, regardless of treatment indication, was 54% (27/50), 80% (8/10), and 81% (13/16) among WT, Y640F, and D661Y groups, respectively. Mutated (Y640F+D661Y combined) patients showed a significantly higher ORR to CTX than WT patients (81% versus 54%, p=0.02 by chi-square test). Patients with Y640F mutations and neutropenia showed significantly higher ORR to MTX than WT patients with neutropenia (69% versus 47%, p=0.05 by chi-square test), and a trend toward higher ORR than D661Y patients with neutropenia (p=0.06 by chi-square test).

Conclusions In this retrospective review, T-LGL patients with Y640F or D661Y STAT3 mutations demonstrated higher response rates to CTX than WT patients. Patients with Y640F mutation who had neutropenia demonstrated higher response rates to MTX than WT patients with neutropenia.