ABSTRACT
Bone marrow fibrosis (MF) reflects stromal remodeling and has been associated with treatment resistance and adverse outcomes in hematologic malignancies; however, its clinical significance in acute lymphoblastic leukemia (ALL) remains uncertain. We retrospectively analyzed 103 patients with newly diagnosed ALL and documented MF grades between 2018 and 2023, comparing patients with MF grades 0–1 and those with MF grades 2–3. Higher‐grade MF was present in 50 patients (48.5%). B‐ALL accounted for a greater proportion of cases in the MF 2–3 group than in the MF 0–1 group (94.0% vs. 69.8%; nominal p = 0.002), and this difference remained statistically significant after false discovery rate correction. No mutation‐level difference between the MF groups remained significant after correction for multiple comparisons. In Cox regression, MF 2–3 was associated with a lower observed hazard of death compared with MF 0–1 (adjusted HR, 0.26; 95% CI, 0.12–0.55; p < 0.001). A similar association was observed in a sensitivity analysis restricted to patients with B‐ALL (adjusted HR, 0.30; 95% CI, 0.13–0.70; p = 0.005). Given the retrospective design, limited number of deaths, and potential residual confounding, this unexpected inverse association should be considered exploratory and should not be interpreted as evidence of a biologically protective effect of MF. In conclusion, higher‐grade MF was common in newly diagnosed ALL and was associated with B‐lineage disease. An unexpected inverse association between MF grade and observed mortality was identified in this cohort and persisted in the B‐ALL‐restricted sensitivity analysis. External validation is required before MF can be considered for prognostic stratification or treatment decision‐making.
Keywords: acute lymphocytic leukemia, bone marrow fibrosis, hematopoietic stem cell transplantation, prognostication
1. Introduction
Acute lymphocytic leukemia (ALL) represents a clinically and biologically heterogeneous hematologic malignancy characterized by uncontrolled proliferation of immature B‐ or T‐lymphoid precursors. Contemporary risk‐adapted therapeutic strategies, incorporating variables such as age, leukocytosis, immunophenotypic features, cytogenetic and molecular abnormalities, and measurable residual disease (MRD), have significantly improved outcomes through optimized induction regimens, risk‐stratified consolidation therapies, and targeted agents, including tyrosine kinase inhibitors for Philadelphia chromosome‐positive disease and CD19/CD22‐directed chimeric antigen receptor (CAR) T‐cell therapies for relapsed/refractory cases [1, 2]. Nevertheless, a substantial proportion of patients experience therapeutic failure attributable to intrinsic leukemia cell resistance mechanisms or permissive bone marrow microenvironmental crosstalk. Emerging evidence implicates bone marrow fibrosis (MF), which is a dynamic stromal remodeling process marked by abnormal extracellular matrix deposition, as a potential microenvironmental determinant of treatment resistance [3]; however, its pathobiological significance and prognostic implications in ALL remain poorly characterized.
In the 2022 WHO classification, myelodysplastic neoplasms (MDS) are defined by morphological and/or genetic features. Among morphologically defined categories, MDS with increased blasts includes MDS‐IB1, MDS‐IB2, and MDS with fibrosis (MDS‐f) [4, 5]. While bone MF is known to harbor disease‐specific prognostic implications across hematologic malignancies [6, 7], its impact remains heterogeneous.
In acute myeloid leukemia (AML), moderate‐to‐severe MF (2–3 grade) correlates with complex cytogenetics and JAK2 mutations, conferring reduced median overall survival, particularly in elderly patients refractory to intensive chemotherapy [8]. Conversely, reports in other malignancies yield varying results: in chronic myeloid leukemia (CML), higher baseline MF grades have been linked to conflicting outcomes, with some suggesting improved survival potentially related to treatment effects [9], while others associate it with a reduced likelihood of achieving treatment‐free remission [10]. Similarly, in multiple myeloma and chronic lymphocytic leukemia, some retrospective data suggest that increasing MF severity correlates with inferior progression‐free and overall survival, respectively.
Despite these advancements, a comprehensive understanding of MF's role in ALL remains elusive. Although bone marrow fibrosis in ALL has been described previously, including in pediatric ALL cohorts, its clinicopathological relevance in contemporary ALL populations remains incompletely defined. We aimed to delineate the distinct clinicopathological features of MF in a contemporary, mixed‐age ALL cohort and, importantly, to explore whether MF status may be associated with clinical outcomes, including patterns observed in patients who underwent HSCT—a critical aspect not addressed in prior literature. Therefore, we conducted this retrospective study to provide a comprehensive clinical and pathological profile of MF in a mixed‐age cohort of ALL patients, explore its association with survival using multivariable survival analysis, and describe baseline clinical variables associated with outcomes in patients with different MF grades. We hope to provide descriptive data that may inform future validation studies in this specific subgroup of patients.
2. Methods
2.1. Study Design
This retrospective study analyzed clinical data from 103 newly diagnosed ALL patients at Xinqiao Hospital of Army Medical University between January 2018 and November 2023. In our daily clinical practice, bone marrow biopsies were performed in the vast majority of patients with newly diagnosed ALL.
The inclusion criteria were as follows: fulfillment of the diagnostic criteria for ALL; complete medical records, including follow‐up data; adequate and well‐preserved bone marrow biopsy specimens; available genetic and molecular testing; and documented antileukemic treatment and response assessment. Follow‐up through December 2024 was conducted via medical record review or telephone interviews. This study has received ethical approval from both our institutional ethics committee and the Chinese Ethics Committee for Clinical Trial Registration (Approval No.: ChiECRCT‐20180145), in accordance with the principles of the Declaration of Helsinki.
2.2. Marrow Fibrosis‐Related Examination Methods
MF was assessed by two senior hematopathologists through biopsy examinations centrally at our institution. Bone marrow trephine biopsy specimens were fixed in 10% neutral‐buffered formalin, decalcified, paraffin‐embedded, sectioned at 3–4 μm, and stained with hematoxylin and eosin, and reticulin silver staining. Reticulin staining was performed using a reticulin staining reagent (DMRD0162; Shenzhen Dartmon Biotechnology Co. Ltd., Shenzhen, China) on an SS330 PLUS automated special staining system. CD20 immunohistochemistry was performed using a ready‐to‐use mouse monoclonal anti‐human CD20 antibody (clone L26, catalog no. KIT‐0001; Fuzhou Maixin Biotechnology Development Co. Ltd., Fuzhou, China) on an Autostainer Link 48 automated staining platform (Agilent Technologies). Representative microscopic images were acquired using an Olympus BX63 microscope equipped with an Olympus DP74 digital camera (Olympus, Tokyo, Japan). MF grading was performed according to the WHO (2016) MF criteria, with all cases stratified into MF 0–1 and MF 2–3 cohorts. To ensure accuracy, two senior hematopathologists independently evaluated the fibrosis severity. The reviewers were blind to the patients' clinical data and treatment outcomes. In instances where the initial grades differed, a final consensus score was determined through joint re‐evaluation using a multi‐head microscope. Only cases with adequate biopsy specimens (containing intact bony trabeculae) were included in the analysis. MF grade was determined from the diagnostic bone marrow biopsies. Post‐treatment bone marrow biopsies were performed only when clinically indicated and were not obtained at prespecified time points. Therefore, serial changes in MF grade during treatment were not systematically analyzed.
2.3. Molecular and Genetic Analysis
Genetic characterization was performed using conventional cytogenetics (G‐banding), fluorescence in situ hybridization (FISH) with specific probes (e.g., BCR::ABL1 and KMT2A break‐apart probes), and targeted next‐generation sequencing (NGS).
2.4. Treatment and Post‐Remission Management
Treatment strategies reflected routine clinical practice during the study period and varied according to age and disease characteristics. Initial therapy was selected based on age, immunophenotypic lineage, BCR::ABL1 status, and clinical fitness. Pediatric patients generally received pediatric multiagent chemotherapy, whereas adults received age‐ and fitness‐adapted multiagent regimens. Patients with BCR::ABL1‐positive ALL received tyrosine kinase inhibitor‐containing therapy when indicated. Post‐remission treatment was adapted to treatment response and generally included consolidation and/or maintenance therapy, with targeted therapy as appropriate. Allogeneic HSCT was generally considered for patients with high‐risk disease features, persistent MRD or other suboptimal treatment response, relapsed or refractory disease, and suitable transplant eligibility with an available donor. Treatment response was assessed after completion of the first induction course. Complete remission (CR) was defined as < 5% blasts in the bone marrow, absence of circulating leukemic blasts and extramedullary disease, an absolute neutrophil count of ≥ 1.0 × 109/L, and a platelet count of ≥ 100 × 109/L. For the present analysis, only CR achieved after the first induction course was counted; responses achieved only after subsequent re‐induction or salvage therapy were not classified as CR.
2.5. Measurable Residual Disease Assessment
MRD data were retrospectively extracted from the medical records. Because MRD testing was not performed at a uniform protocol‐defined time point across this retrospective cohort, we used the earliest evaluable MRD result documented between diagnosis and the first documented remission assessment. When multiple MRD measurements were available within this interval, only the earliest evaluable result was used for the present analysis. MRD status was classified as positive or negative according to the contemporaneous clinical laboratory report, whereas cases without an interpretable result were categorized as unevaluable. Given the heterogeneous timing of MRD assessment, MRD data were summarized descriptively and were not included as covariates in the survival models.
2.6. Statistical Analysis
Categorical variables were compared using Pearson's chi‐squared test or Fisher's exact test, as appropriate. Non‐normally distributed continuous variables were compared using the Wilcoxon rank‐sum test. For the 16 between‐group comparisons presented in Table 1, p values were adjusted for multiple testing using the Benjamini‐Hochberg false discovery rate procedure. Both nominal and adjusted p values are reported. Factors associated with CR were evaluated using univariable and multivariable logistic regression. OS was defined as the interval from diagnosis to death from any cause; patients who were alive or lost to follow‐up were censored at the date of last known contact. Factors associated with OS were evaluated using Cox proportional hazards models. Allogeneic HSCT was modeled as a time‐dependent covariate in a start‐stop Cox model, with patients contributing unexposed person‐time before transplantation and exposed person‐time thereafter. To limit overfitting given the number of outcome events, the multivariable Cox model was kept parsimonious and included age per 10‐year increase, KMT2A abnormality, MF grade (0–1 vs. 2–3) as the primary exposure of interest, and allogeneic HSCT modeled as a time‐dependent covariate. Because leukemia lineage differed substantially between the MF groups, a sensitivity analysis restricted to patients with B‐ALL was performed using the same Cox model specification. Ties were handled using the Efron method. Analyses were performed using R version 4.4.3 and IBM SPSS Statistics version 30. All tests were two‐sided, and p < 0.05 was considered statistically significant.
TABLE 1.
Baseline features in newly diagnosed ALL patients by MF groups.
| Parameter | MF 0–1 | MF 2–3 | Overall | p | FDR‐adjusted p |
|---|---|---|---|---|---|
| (N = 53) | (N = 50) | (N = 103) | |||
| Age, year | 0.807 | ||||
| Mean (SD) | 28.2 (16.0) | 29.2 (17.3) | 28.7 (16.6) | ||
| Median [Min, Max] | 24.0 [2.00, 58.0] | 26.0 [2.00, 66.0] | 25.0 [2.00, 66.0] | ||
| < 18 | 18 (34.0%) | 17 (34.0%) | 35 (34.0%) | ||
| 18–35 | 20 (37.7%) | 17 (34.0%) | 37 (35.9%) | ||
| > 35 | 15 (28.3%) | 16 (32.0%) | 31 (30.1%) | ||
| Sex | 0.871 | ||||
| Female | 22 (41.5%) | 19 (38.0%) | 41 (39.8%) | ||
| Male | 31 (58.5%) | 31 (62.0%) | 62 (60.2%) | ||
| Type | 0.002 | 0.032 | |||
| B‐ALL | 37 (69.8%) | 47 (94.0%) | 84 (81.6%) | ||
| T‐ALL | 16 (30.2%) | 3 (6.0%) | 19 (18.4%) | ||
| WBC, × 109/L | 0.105 | ||||
| Mean (SD) | 95.9 (162) | 43.7 (62.6) | 70.6 (127) | ||
| Median [Min, Max] | 32.9 [0.690, 920] | 16.0 [0.690, 297] | 27.0 [0.690, 920] | ||
| HGB, g/L | 0.187 | ||||
| Mean (SD) | 92.7 (34.6) | 83.3 (27.4) | 88.1 (31.5) | ||
| Median [Min, Max] | 88.0 [35.0, 179] | 79.5 [49.0, 170] | 81.0 [35.0, 179] | ||
| PLT, × 109/L | 0.950 | ||||
| Mean (SD) | 67.4 (59.2) | 81.2 (88.0) | 74.1 (74.5) | ||
| Median [Min, Max] | 45.0 [5.00, 317] | 51.0 [5.00, 388] | 49.0 [5.00, 388] | ||
| BCR::ABL1 | 14 (26.4%) | 17 (34.0%) | 31 (30.1%) | 0.533 | |
| IKZF1 | 6 (11.3%) | 5 (10.0%) | 11 (10.7%) | 1.000 | |
| NOTCH1 | 9 (17.0%) | 2 (4.0%) | 11 (10.7%) | 0.053 | 0.283 |
| NRAS | 5 (9.4%) | 6 (12.0%) | 11 (10.7%) | 0.756 | |
| KRAS | 1 (1.9%) | 7 (14.0%) | 8 (7.8%) | 0.028 | 0.224 |
| PAX5 | 3 (5.7%) | 4 (8.0%) | 7 (6.8%) | 0.710 | |
| KMT2A | 6 (11.3%) | 1 (2.0%) | 7 (6.8%) | 0.113 | |
| KMT2D | 3 (5.7%) | 4 (8.0%) | 7 (6.8%) | 0.710 | |
| Complex karyotype | 2 (3.8%) | 5 (10.0%) | 7 (6.8%) | 0.261 | |
| Risk stratification | 0.191 | ||||
| Standard | 10 (18.9%) | 16 (32.0%) | 26 (25.2%) | ||
| High | 43 (81.1%) | 34 (68.0%) | 77 (74.8%) |
Note: p values were adjusted across the 16 between‐group comparisons using the Benjamini–Hochberg false discovery rate procedure. The bold values indicate statistical significance (p < 0.05).
Abbreviations: ALL, acute lymphoblastic leukemia; HGB, hemoglobin; MF, marrow fibrosis; PLT, platelets; WBC, white blood cell.
3. Results
3.1. Patient Characteristics
Among 112 ALL patients treated from January 2018 to November 2023, 103 had documented MF status. The exclusion of the remaining 9 patients was strictly due to technical reasons (e.g., insufficient biopsies specimen, severe crush artifact, or poor preservation quality) rather than based on any specific clinical characteristics or bias in patient selection. Through histopathological stratification, patients were classified into two groups: the MF 0–1 group (no or mild fibrosis) and the MF 2–3 group (moderate or severe fibrosis). The MF 2–3 group exhibited markedly increased reticulin fibrosis compared with the MF 0–1 group (Figure 1). The cohort comprised 53 MF 0–1 cases (51.4%; MF‐0: 10 cases [9.7%]; MF‐1: 43 [41.7%]) and 50 MF 2–3 cases (48.5%; MF‐2: 33 [32.0%]; MF‐3: 17 [16.5%]).
FIGURE 1.
Representative bone marrow pathological findings in patients with ALL. (A) Hematoxylin and eosin (H&E) staining. (B) CD20 immunohistochemical staining. (C) Gomori reticulin staining showing MF 0–1. (D) Gomori reticulin staining showing MF 2–3. Scale bars = 50 μm. ALL, acute lymphoblastic leukemia; MF, marrow fibrosis.
Analyzed variables included age, sex (female or male), ALL type (B‐ALL or T‐ALL), presenting blood counts (WBC, HGB, PLT), genetic abnormalities (e.g., BCR::ABL1, IKZF1, NOTCH1, NRAS, KRAS, PAX5, KMT2A, KMT2D), cytogenetic profiles, HSCT administration, and treatment outcomes (CR and relapse). Comparative analyses of clinical characteristics between groups are presented in Table 1. After Benjamini‐Hochberg correction for the 16 comparisons presented in Table 1, the difference in ALL lineage remained statistically significant (FDR‐adjusted p = 0.032), whereas none of the mutation‐level comparisons remained significant.
The cohort demonstrated a median age of 25 years (range 2 to 66 years), comprising 35 pediatric ALL cases (< 18 years, 34.0%) and 68 adults (≥ 18 years, 66.0%). MF 2–3 exhibited significantly higher B‐ALL prevalence than the MF 0–1 group (94.0% vs. 69.8%, p = 0.002), indicating T‐ALL's reduced association with severe fibrosis (6.0% vs. 30.2%). No intergroup differences emerged in age, sex, or complete blood count at initial diagnosis (all p > 0.05; Figure 2A).
FIGURE 2.
Baseline peripheral blood counts, genetic alteration profiles, and treatment modalities according to marrow fibrosis grade in patients with ALL. (A) Distributions of white blood cell (WBC) count, hemoglobin (HGB), and platelet (PLT) count in the MF 0–1 and MF 2–3 groups. (B) Frequencies of selected genetic alterations in the overall cohort and according to MF grade. (C) Sankey diagram showing the distribution of HSCT and CAR‐T treatment between the MF 0–1 and MF 2–3 groups. (D) Proportions of patients receiving neither treatment, HSCT only, CAR‐T only, or both HSCT and CAR‐T in the two MF groups. ALL, acute lymphoblastic leukemia; CAR‐T, chimeric antigen receptor T‐cell therapy; HGB, hemoglobin; HSCT, hematopoietic stem cell transplantation; MF, marrow fibrosis; PLT, platelet; WBC, white blood cell.
Nominally, KRAS mutations were more frequent in the MF 2–3 group than in the MF 0–1 group (14.0% vs. 1.9%; nominal p = 0.028), although this difference did not remain statistically significant after FDR correction. NOTCH1 alterations trended toward MF 0–1 predominance (17.0% vs. 4.0%, p = 0.053). BCR::ABL1, IKZF1, NRAS, PAX5, KMT2A, and KMT2D displayed comparable frequencies (all p > 0.05; Figure 2B). Complex karyotype (5 or more chromosomal abnormalities) occurred in 7 patients (6.8%), numerically enriched in the MF 2–3 group (10.0% vs. 3.8%, p = 0.261) without statistical significance.
MRD status within the defined assessment window was evaluable in 94 of 103 patients (91.3%). Among these patients, 40 (42.6%) were MRD‐positive and 54 (57.4%) were MRD‐negative, whereas 9 patients (8.7%) had no evaluable MRD result. Because the timing of MRD assessment was not uniform across the cohort, these data were used for descriptive comparison only.
3.2. Therapeutic Interventions Analysis
The overall CR rate after first induction was 64.1% among ALL patients (66/103), with almost equivalent efficacy observed across the two MF groups (64.2% [34/53] vs. 64.0% [32/50], p = 1.000). Univariable and multivariable logistic regression analyses identified age as an independent risk factor for CR achievement (Table 2). Patients > 35 years demonstrated a reduced likelihood of CR compared to those under 18 years (OR = 0.12, 95% CI: 0.03–0.43, p = 0.002). Analysis revealed no adverse impact of moderate–severe MF 2–3 fibrosis on CR rate after the first induction compared with MF 0–1 (OR = 0.99, 95% CI: 0.44–2.23, p = 0.987).
TABLE 2.
Logistic regression analysis of factors associated with complete remission after first induction in the study cohort.
| Variables | Univariate analysis | Multivariate analysis | ||
|---|---|---|---|---|
| OR (95% CI) | p | OR (95% CI) | p | |
| Age, year | ||||
| < 18 (n = 35) | Reference | Reference | ||
| 18–35 (n = 37) | 0.37 (0.12–1.03) | 0.063‐ | 0.33 (0.11–0.96) | 0.046 |
| > 35 (n = 31) | 0.27 (0.09–0.77) | 0.017 | 0.12 (0.03–0.43) | 0.002 |
| Sex | ||||
| Female (n = 41) | Reference | |||
| Male (n = 62) | 0.88 (0.38–2.00) | 0.760 | ||
| Type | ||||
| B‐ALL (n = 84) | Reference | |||
| T‐ALL (n = 19) | 0.73 (0.26–2.06) | 0.535 | ||
| BCR::ABL1 (n = 31) | 1.94 (0.79–5.16) | 0.164 | 4.47 (1.46–16.38) | 0.014 |
| Risk stratification | ||||
| Standard (n = 26) | Reference | |||
| High (n = 77) | 0.58 (0.20–1.49) | 0.272 | ||
| MF | ||||
| 0–1 (n = 53) | Reference | |||
| 2–3 (n = 50) | 0.99 (0.44–2.23) | 0.987 | ||
Note: The bold values indicate statistical significance (p < 0.05).
Abbreviations: ALL, acute lymphoblastic leukemia; CI, confidence interval; CR, complete remission assessed after the first induction course; MF, marrow fibrosis; OR, odds ratio.
Unlike most hematologic malignancies, ALL treatment protocols are age‐stratified (pediatric or adult), primarily manifested in chemotherapy intensity, agent selection, and transplantation strategies. We focused on HSCT therapy in ALL patients with concurrent MF; of 103 patients, 77 (74.8%) underwent HSCT, showing comparable rates between MF 0–1 (38 cases, 71.7%) and MF 2–3 groups (39 cases, 78.0%). CAR‐T therapy was limited to 10 cases (9.7%), distributed as 3 (5.7%) vs. 7 (14.0%) across two MF groups (p = 0.193). Eight patients received both therapeutic strategies, while 24 underwent neither intervention. Comparative treatment selection patterns between cohorts are detailed in Figure 2C,D.
3.3. Survival
During a median follow‐up of 22 months, 31 deaths occurred. In univariable Cox regression analyses, older age per 10‐year increase (HR, 1.28; 95% CI, 1.05–1.57; p = 0.017) and KMT2A abnormality (HR, 4.12; 95% CI, 1.40–12.08; p = 0.010) were associated with a higher hazard of death, whereas MF 2–3 compared with MF 0–1 was associated with a lower observed hazard of death (HR, 0.34; 95% CI, 0.15–0.73; p = 0.006). Allogeneic HSCT, modeled as a time‐dependent covariate, was also associated with a lower observed hazard of death (HR, 0.21; 95% CI, 0.10–0.43; p < 0.001). In the multivariable model including age, KMT2A abnormality, MF grade, and time‐dependent allogeneic HSCT, older age (adjusted HR, 1.30; 95% CI, 1.08–1.57; p = 0.006) and KMT2A abnormality (adjusted HR, 3.00; 95% CI, 1.29–6.95; p = 0.011) remained associated with a higher hazard of death, whereas MF 2–3 remained associated with a lower observed hazard of death (adjusted HR, 0.26; 95% CI, 0.12–0.55; p < 0.001). Time‐dependent allogeneic HSCT was likewise associated with a lower observed hazard of death (adjusted HR, 0.14; 95% CI, 0.06–0.33; p < 0.001) (Table 3).
TABLE 3.
Cox proportional hazards regression analysis of OS in the study cohort.
| Variables | Univariable analysis | Multivariable analysis | ||
|---|---|---|---|---|
| HR (95% CI) | p | HR (95% CI) | p | |
| Age, per 10‐year increase | 1.28 (1.05–1.57) | 0.017 | 1.30 (1.08–1.57) | 0.006 |
| Sex | ||||
| Female | Reference | |||
| Male | 1.14 (0.55–2.38) | 0.727 | ||
| Type | ||||
| B‐ALL | Reference | |||
| T‐ALL | 1.42 (0.61–3.30) | 0.417 | ||
| BCR::ABL1 | 1.49 (0.72–3.08) | 0.279 | ||
| IKZF1 | 1.25 (0.44–3.58) | 0.677 | ||
| NOTCH1 | 1.25 (0.43–3.58) | 0.682 | ||
| KMT2A | 4.12 (1.40–12.08) | 0.010 | 3.00 (1.29–6.95) | 0.011 |
| ABL:T315I | 2.14 (0.65–7.06) | 0.211 | ||
| Risk stratification | ||||
| Standard | Reference | |||
| High | 2.66 (0.93–7.62) | 0.068 | ||
| MF | ||||
| 0–1 | Reference | |||
| 2–3 | 0.34 (0.15–0.73) | 0.006 | 0.26 (0.12–0.55) | < 0.001 |
| Allogeneic HSCT, time‐dependent covariate | 0.21 (0.10–0.43) | < 0.001 | 0.14 (0.06–0.33) | < 0.001 |
Note: Allogeneic HSCT was modeled as a time‐dependent covariate in a start–stop Cox model. Ties were handled using the Efron method. The bold values indicate statistical significance (p < 0.05).
Abbreviations: ALL, acute lymphoblastic leukemia; CI, confidence interval; HR, hazard ratio; HSCT, hematopoietic stem cell transplantation; MF, marrow fibrosis; OS, overall survival.
Because leukemia lineage differed substantially between the MF groups, we performed a sensitivity analysis restricted to the 84 patients with B‐ALL. Within this subgroup, MF 2–3 was associated with a lower observed hazard of death in univariable analysis (HR, 0.34; 95% CI, 0.15–0.79; p = 0.012) and in the adjusted model including age, KMT2A abnormality, MF grade, and time‐dependent allogeneic HSCT (adjusted HR, 0.30; 95% CI, 0.13–0.70; p = 0.005; Table S1).
4. Discussion
We characterized the clinicopathological features and exploratory outcome associations of ALL patients with concomitant marrow fibrosis. Nearly half of the patients had MF Grade 2–3 at diagnosis, and the distribution of ALL lineage differed between the MF groups. The MF 2–3 group contained a higher proportion of B‐ALL cases than the MF 0–1 group (94.0% vs. 69.8%). This difference remained statistically significant after correction for multiple comparisons, which aligns with prior evidence [11]. Lineage imbalance may partly account for observed associations and requires validation.
KMT2A abnormalities were independently associated with inferior OS in both univariable analysis (HR, 4.12; 95% CI, 1.40–12.08; p = 0.010) and multivariable analysis (HR, 3.00; 95% CI, 1.29–6.95; p = 0.011), consistent with their established adverse prognostic role in acute leukemia [12, 13, 14]. This finding supports the need for improved risk assessment and therapeutic strategies for this molecular subgroup [15, 16].
Compared with patients aged < 18 years, those aged > 35 years had lower odds of achieving CR (OR, 0.12; 95% CI, 0.03–0.43; p = 0.002). This association may reflect age‐related differences in disease biology, treatment tolerance, and comorbidity burden, although these factors were not directly evaluated in the present study.
Unexpectedly, MF 2–3 was associated with a lower observed hazard of death in the overall cohort, and a similar association was observed in the sensitivity analysis restricted to patients with B‐ALL. This finding should not be interpreted as evidence that marrow fibrosis is biologically protective. Previous studies of MF in ALL have been limited and have yielded heterogeneous findings regarding its relationship with disease phenotype, treatment response, and outcome. In the present cohort, only 31 deaths occurred; treatment strategies were heterogeneous and nonrandomized, and several potentially important prognostic and treatment‐related factors could not be uniformly incorporated into the survival models. Although restriction to B‐ALL reduced the potential influence of the marked lineage imbalance, residual confounding by unmeasured disease biology, treatment selection, and other clinical factors cannot be excluded. Baseline MF may therefore represent a surrogate for other biological or clinical characteristics rather than a causal determinant of survival. Accordingly, the observed inverse association should be considered exploratory and hypothesis‐generating and requires validation in an independent cohort.
Allogeneic HSCT was associated with a lower hazard of death when modeled as a time‐dependent covariate. Although this modeling approach reduces immortal time bias, the observed association remains susceptible to substantial confounding by indication. In clinical practice, transplantation was selected according to disease‐risk features, treatment response, MRD when available, relapse/refractory status, transplant eligibility, donor availability, and other clinical considerations. Accordingly, the present finding should be interpreted as an observational association and not as evidence of a causal survival benefit from HSCT.
Only a small number of patients with MF Grade 2–3 received CAR‐T therapy in this cohort, and treatment‐response data were incomplete. Therefore, the present study could not determine whether marrow fibrosis influenced the efficacy of CAR‐T therapy. Experimental studies suggest that a fibrotic marrow microenvironment may affect immune‐cell trafficking and function [17]. However, only seven patients with MF Grade 2–3 received CAR‐T therapy in this cohort, and treatment‐response data were insufficient to assess whether MF influenced CAR‐T efficacy. This question requires evaluation in larger, prospectively characterized cohorts.
Several limitations should be acknowledged. First, the retrospective single‐center design and modest sample size limited statistical power, particularly for subgroup analyses. Second, treatment strategies were heterogeneous across age groups, biological subtypes, and calendar periods, leaving residual confounding by indication despite the time‐dependent HSCT analysis. Third, MRD testing was not performed at a uniform protocol‐defined time point. Although the earliest evaluable MRD result between diagnosis and the first documented remission assessment was retrospectively summarized, the heterogeneous timing of assessment precluded robust incorporation of MRD into the multivariable survival models. Finally, repeat bone marrow biopsies were not routinely obtained at standardized time points, preventing systematic assessment of whether marrow fibrosis regressed, persisted, or progressed during treatment.
Future multicenter studies should incorporate standardized diagnostic and serial bone marrow biopsies, comprehensive MRD assessment, detailed treatment timing, transplantation status, and longitudinal clinical outcomes. Quantitative pathological assessment and integration of genomic and microenvironmental data may help clarify whether MF is primarily a disease‐associated feature or independently contributes to treatment response and prognosis in ALL.
5. Conclusions
In summary, higher‐grade marrow fibrosis was common in this cohort of newly diagnosed ALL patients and was associated with a greater proportion of B‐lineage disease. No mutation‐level comparison remained statistically significant after correction for multiple testing. Older age and KMT2A abnormalities were associated with inferior OS, whereas allogeneic HSCT modeled as a time‐dependent covariate was associated with a lower hazard of death. However, the prognostic and treatment‐stratification value of MF grade remains uncertain and requires prospective validation using standardized longitudinal pathological assessment.
Author Contributions
S.‐H.L., C.Z., and X.Z. designed research. S.‐H.L. and Y.C. performed research. Lei.G., Li.G., Y.‐M.F., Q.W., J.R., and P.‐Y.K. carried out patient management. S.‐H.L., C.‐X.R., W.‐C.Y., J.L., and X.‐G.P. collected data. S.‐H.L., Y.C., and C.Z. analyzed and interpreted data. S.‐H.L. and Y.C. performed statistical analysis. Y.C. wrote the manuscript. All authors made final approval of the manuscript.
Funding
This work was supported by grants from the National Natural Science Foundation of China (82370181), Chongqing Science and Health Collaborative Major Project on Medical Science and Technology Innovation (2024DBXM004), the Key Project of Chongqing Natural Science Foundation Innovation and Development Joint Fund (CSTB2025NSCQ‐LZX0048), and the Clinical Research Special Project of the Second Affiliated Hospital, the Army Medical University (2024F010).
Disclosure
The views expressed in this manuscript are solely those of the authors and do not necessarily represent the official position of Xinqiao Hospital, Army Medical University, or any affiliated funding bodies.
Ethics Statement
The study was approved by the Medical Ethics Committee of Xinqiao Hospital of Army Medical University and the Chinese Ethics Committee for Clinical Trial Registration (Approval No.: ChiECRCT‐20180145).
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Table S1: Cox regression analysis of OS restricted to patients with B‐ALL.
Acknowledgements
We thank all patients, their families, and the nurses and physicians at the hematology medical center for contributing data to our research.
Contributor Information
Xi Zhang, Email: zhangxi@tmmu.edu.cn.
Cheng Zhang, Email: chzhang2014@tmmu.edu.cn.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Table S1: Cox regression analysis of OS restricted to patients with B‐ALL.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.