Prognostic Significance of Serum-Soluble Endoglin (CD105) Levels in Patients with Acute Myeloid Leukemia

Abstract

Objective

We investigated the serum-soluble endoglin (CD105) levels and their prognostic significance in patients with acute myeloid leukemia (AML), given that angiogenesis, stimulated by vascular endothelial cells, is known to increase during AML development, and serum-soluble endoglin is a transmembrane protein that induces the activation and proliferation of these cells.

Materials and Methods

The study included 30 newly diagnosed or relapsed AML patients followed at the Hematology Clinic of Atatürk University Faculty of Medicine Hospital and 30 healthy individuals. The demographic characteristics, hemogram and biochemical parameters, performance scores, flow cytometry results, cytogenetic and molecular laboratory findings, follow-up durations, survival statuses, chemotherapy protocols, and patients' responses to chemotherapy were recorded. Serum-soluble endoglin was measured before and after chemotherapy in AML patients.

Results

Serum-soluble endoglin levels in AML patients before and after treatment were not significantly different (p = 0.494). The pretreatment serum-soluble endoglin (CD105) levels in AML patients were similar to those of the control group (p = 0.264). Endoglin (CD105) levels in the group that achieved remission after induction therapy and the refractory group were not significantly different (p = 0.245). Serum-soluble endoglin (CD105) levels were also similar between surviving patients and those who died (p = 0.07).

Conclusion

Serum-soluble endoglin (CD105) levels may not hold diagnostic or prognostic significance in AML patients.

 

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Keywords

acute myeloid leukemia - biomarker - serum-soluble endoglin - CD105 - prognosis

Introduction

Acute myeloid leukemia (AML) is a hematological malignancy characterized by the uncontrolled proliferation of myeloid precursor cells in the bone marrow. It is the most common type of acute leukemia in adults.[1] The classification of AML is conducted by the World Health Organization based on clinical, morphological, immunophenotypic, and genetic characteristics.[2] Various genetic, acquired, and environmental risk factors have been identified in the etiology of AML. The most significant include age, cytogenetic/molecular laboratory findings, exposure to radiation or cytotoxic agents, and a history of hematological malignancies.[3] [4] [5] [6] [7] [8] In recent years, with a better understanding of the genomic background of AML pathogenesis, it has been shown that the genetic characteristics of patients are the most crucial prognostic risk factor.[9] However, despite these advances, the prognosis of patients within the same risk group may still vary. Therefore, there is a need for new biomarkers to determine the prognosis of the disease better.[10]

Serum endoglin (CD105) is a transmembrane protein that is a part of the transforming growth factor-β signaling complex. It stimulates the activation and proliferation of endothelial cells and is overexpressed in vascular endothelium where angiogenesis is excessive. It is secreted by healthy cells such as vascular endothelial cells, fibroblasts, hematopoietic system cells, and vascular smooth muscle cells. Additionally, it has been detected in the vascular endothelium of various solid organ malignancies, including angiosarcoma, liver, stomach, breast, and endometrial carcinoma, as well as in hematological malignancies such as AML and acute lymphoblastic leukemia.[11] [12] [13] [14] Serum endoglin (CD105) levels have also been reported as a potential prognostic biomarker in AML cases.[11]

In this study, we aimed to determine the serum endoglin (CD105) levels and their prognostic value in newly diagnosed or relapsed AML patients followed at the Atatürk University Hematology Clinic.

 

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Materials and Methods

Design and Setting

This study included 30 newly diagnosed or relapsed AML patients followed at the Hematology Clinic of Atatürk University Faculty of Medicine Hospital and 30 healthy individuals serving as the control group.

 

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Patients Recruitment

For patient recruitment, individuals aged 18 years or older with a confirmed diagnosis of AML, either newly diagnosed or relapsed, were eligible for inclusion, provided they gave informed consent. Patients were excluded if they presented with other active malignancies (excluding AML) and suffered from severe systemic diseases or uncontrolled comorbidities (such as severe heart failure, uncontrolled diabetes, or active severe infection) that could significantly affect their prognosis or interfere with the study's primary outcomes. Additionally, individuals who had received any prior AML-specific chemotherapy or targeted therapy, other than for a relapsed setting, were excluded to ensure the assessment of initial or postinduction soluble endoglin levels in a consistent context.

 

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Sample Size Calculation

A priori power analysis was conducted using G*Power software (version 3.1.9.7), assuming an effect size of 0.8, α = 0.05, and power (1–β) = 0.80. The minimum required sample size was calculated as 26. Therefore, the sample size of 30 AML patients was considered adequate for detecting clinically meaningful differences. In addition, since the subgroups have a balanced distribution, the results can be interpreted confidently.

 

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The Experimental Protocol

The demographic characteristics, complete blood count and biochemical parameters, C-reactive protein and sedimentation values, Eastern Cooperative Oncology Group (ECOG) performance scores, flow cytometry results, and cytogenetic and molecular findings were recorded. Additionally, the patients' applied chemotherapy protocols, treatment responses, follow-up durations, and survival statuses were documented. Blood samples were collected from 30 AML patients at their initial admission to the clinic and after the first cycle of chemotherapy (after recovery from neutropenia or on day 28). Blood samples from the 30 healthy control individuals were also collected, centrifuged, and stored at –80°C. On the analysis day, samples were gradually thawed at –20°C, then at +4°C, and finally at room temperature. Serum-soluble endoglin (CD105) levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit (Human Soluble Endoglin ELISA Kit, Catalog No: E0316Hu, Bioassay Technology Laboratory, China). The kit, designed for detecting human endoglin levels in urine, cell culture supernatant, serum, plasma, and tissue homogenates, had a measurement range of 0.5 to 200 ng/mL, a sensitivity of 0.25 ng/mL, and an intra-assay coefficient of variation of < 10%.

AML risk stratification for all patients in this study was performed according to the 2022 European Leukemia Network (ELN) recommendations. The ELN classification primarily relies on recurrent genetic abnormalities (e.g., t(8;21), inv(16), t(15;17) NPM1 mutations, FLT3-ITD with varying allelic ratios, CEBPA mutations) to categorize patients into favorable, intermediate, and adverse risk groups. In contrast, based on cytogenetics and molecular mutation profiles, the National Comprehensive Cancer Network (NCCN) guidelines for AML classify patients into favorable, intermediate, and poor/adverse-risk groups. While both systems prioritize genetic and molecular factors, the NCCN guidelines can incorporate antecedent hematologic disorders and therapy-related AML into their adverse risk stratification. Although both ELN and NCCN classifications are widely used and show increasing convergence, subtle differences in the specific mutations or genetic combinations and the inclusion of other clinical factors can lead to variations in risk assignment and thus impact comparative analyses with studies utilizing different systems.

 

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Statistical Analysis

Statistical analyses were conducted using IBM SPSS 20 software. Descriptive data were presented as counts and percentages, while continuous variables were expressed as mean ± standard deviation or median (minimum-maximum), as appropriate. Chi-square and Fisher's exact tests were used to compare categorical variables. Kolmogorov–Smirnov test and histogram graphs were used to assess the normality of continuous variables. An independent samples t-test was used for normally distributed data for comparison between groups, while Mann–Whitney U and Kruskal–Wallis tests were applied for nonnormally distributed data. Wilcoxon test was used for repeated measures analysis, and Spearman correlation analysis was performed to assess relationships between variables. Receiver operating characteristic (ROC) curve analysis was employed to determine cutoff values for disease prediction. A p-value of < 0.05 was considered statistically significant.

 

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Results

The sex distribution in both the study and control groups was similar; in both groups, 43.3% (n = 13) of the subjects were male and 56.7% (n = 17) were female (p > 0.99). The average age in the AML group was 44 ± 11.3 years, and in the control group, it was 46 ± 12.9 years (p = 0.72).

In the AML group, 80% (n = 24) were newly diagnosed, and 20% (n = 6) had relapsed AML. Note that 53.3% (n = 16) of the patients had no comorbidities. The ECOG performance scores were as follows: 36.7% (n = 11) had a score of 1, 36.7% (n = 11) had a score of 2, 23.3% (n = 7) had a score of 3, and 3.3% (n = 1) had a score of 4. The median Karnofsky score was 80 (20–90).

In terms of cytogenetic analysis, 20% (n = 6) had t(15,17), 10% (n = 3) had inv(16), 6.7% (n = 2) had trisomy 5, 6.7% (n = 2) had t(8;21), and 6.7% (n = 2) had a 5q deletion. In molecular analysis, 26.7% (n = 8) had FLT3 mutations and 16.7% (n = 5) had NPM1A mutations. Using next-generation sequencing, 63.3% (n = 19) of the cases had no mutations, 13.3% (n = 4) had FLT3 mutations, 13.3% (n = 4) had FLT3 + NPM1A mutations, 3.3% (n = 1) had NPM1A mutations, 3.3% (n = 1) had KRAS/NRAS mutations, and 3.3% (n = 1) had CEBPA mutations. In the ELN risk status analysis, 26.7% (n = 8) of the patients were classified as low-risk, 46.7% (n = 14) as intermediate-risk, and 26.7% (n = 8) as high-risk.

Seventy percent (n = 21) of the patients received intensive remission induction (RI) therapy, while 30% (n = 9) received 5-azacitidine therapy. Note that 56.7% (n = 17) of the patients achieved remission with chemotherapy, while 43.3% (n = 13) resisted treatment. The mean follow-up duration was 30.3 ± 11.5 days, and 26.7% (n = 8) of the patients died due to AML-related causes during the follow-up period.

Pretreatment serum-soluble endoglin (CD105) levels in the AML patients were 42.5 (23–1191) ng/mL, and posttreatment levels were 53.5 (26–878) ng/mL, which were not significantly different (p = 0.494) ([Fig. 1]). There was no significant difference in serum-soluble endoglin (CD105) levels between the control group (39.5 [17–424] ng/mL) and the pretreatment levels in the AML group (p = 0.264). In newly diagnosed AML cases, serum-soluble endoglin (CD105) levels were 42 (27–1191) ng/mL, while in the relapsed cases, the levels were 44.5 (23–439) ng/mL, with no significant difference between them (p = 0.860) ([Fig. 2]).

Fig. 1 Pretreatment and posttreatment serum-soluble endoglin (CD105) levels.

Fig. 2 Serum-soluble endoglin (CD105) levels in the newly diagnosed and relapsed group.

In the AML group, no significant relationship was found between pretreatment soluble endoglin (CD105) levels and sex (p = 0.079) or age (p = 0.283). Serum-soluble endoglin (CD105) levels were 48 (34–1191) ng/mL in ECOG 1 patients, 42 (33–439) ng/mL in ECOG 2 patients, 41 (23–57) ng/mL in ECOG 3 patients, and 33 (33–33) ng/mL in ECOG 4 patients, with no significant differences (p = 0.252).

Statistically significant correlations between pretreatment serum-soluble endoglin (CD105) levels and specific laboratory parameters, assessed using Spearman correlation analysis, are presented in [Table 1]. No significant correlations were found with other laboratory parameters, including leukocyte, neutrophil, lymphocyte, monocyte, platelet, hemoglobin, sedimentation rate, C-reactive protein, uric acid, fibrinogen, D-dimer, prothrombin time, or other flow cytometry markers. No significant relationship was found between pretreatment soluble endoglin (CD105) levels and cytogenetic abnormalities, mutation status (NPM1A, FLT3, KRAS, NRAS, CEBPA), or ELN risk status.

Table 1 Statistically significant correlations between pretreatment serum-soluble endoglin (CD105) levels and laboratory parameters in AML patients

Parameter	Spearman's Rho	p-Value
Eosinophil count	–0.568	0.001
Lactate dehydrogenase	–0.421	0.021
Activated partial thromboplastin time	0.472	0.009
CD11b (flow cytometry)	–0.369	0.045
CD7 (flow cytometry)	–0.383	0.037

Abbreviation: AML, acute myeloid leukemia.

After one cycle of RI therapy, no significant difference in soluble endoglin (CD105) levels was found between the remission group (42 [33–1191] ng/mL) and the resistant group (43 [23–98] ng/mL) (p = 0.245) ([Fig. 3]).

Fig. 3 Serum-soluble endoglin (CD105) levels in the remission group (42 [33–1191] ng/mL) and the resistant group after remission induction therapy.

During the follow-up period, serum-soluble endoglin (CD105) levels were similar between the surviving patients (43.5 [33–1191] ng/mL) and those who died (37 [23–57] ng/mL) (p = 0.07) ([Fig. 4]).

Fig. 4 Serum-soluble endoglin (CD105) levels in the surviving and deceased patients.

ROC curve analysis was performed to evaluate the potential predictability of endoglin (CD105) levels on clinical parameters such as survival status, treatment response, and risk status. However, since statistically significant and clinically usable distinct cutoff values, sensitivity, or specificity could not be obtained for these parameters in the analyses performed, detailed ROC data (cutoff values, sensitivity, and specificity) are not reported in this results section. This suggests that serum-soluble CD105 levels alone may not be a strong predictive biomarker in this cohort.

 

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Discussion

Our study found that serum-soluble endoglin (CD105) levels before and after RI chemotherapy in AML patients were similar. The pretreatment endoglin levels were similar to those of the control group. Moreover, no significant difference in endoglin (CD105) levels was found between the remission and chemotherapy-resistant groups after RI therapy. Serum-soluble endoglin (CD105) levels were similar between patients who survived and those who died during follow-up.

Notably, a near-significant trend was observed between serum-soluble endoglin (CD105) levels and survival status, with surviving patients showing slightly higher median levels than those who died. This finding, while not statistically significant, is clinically noteworthy as it suggests a potential association between CD105 levels and survival outcomes in AML. The lack of statistical significance may be attributed to the limited statistical power of our study, given the sample size of 30 AML patients. Larger studies are needed to explore this trend further, as endoglin's role in angiogenesis and its prognostic implications in other malignancies suggest it may have clinical relevance in AML.

Despite the relatively small sample size of 30 AML patients, the preliminary G*Power analysis indicated sufficient statistical power for this study's primary outcomes, providing a reasonable basis for our findings.

Kauer et al investigated endoglin (CD105) levels in 62 AML patients using flow cytometry to assess cellular expression, reporting no significant difference in CD105 levels between favorable and unfavorable prognosis groups based on the French-American-British (FAB) classification, but higher levels in the unfavorable risk group per NCCN criteria.[11] In contrast, with a smaller sample size of 30 AML patients, our study utilized ELISA to measure soluble CD105 levels in serum and found no significant association with ELN risk groups. The difference in measurement techniques—flow cytometry for cellular expression versus ELISA for soluble levels—likely contributes to these discrepancies, as cellular and soluble CD105 may reflect distinct biological processes. Additionally, the larger sample size in Kauer et al's study may have provided greater statistical power to detect differences in risk group associations.

Placencio-Hickok et al evaluated plasma and cellular endoglin (CD105) in 128 prostate cancer patients using both ELISA and immunohistochemistry, finding that high plasma CD105 levels predicted recurrence-free survival, while increased cellular expression was linked to worse outcomes.[15] Our study, with only 30 AML patients and using ELISA alone, found no prognostic significance for soluble CD105. The larger sample size and dual measurement approach in Placencio-Hickok et al's study may explain their ability to detect prognostic associations, as immunohistochemistry captures tissue-specific expression that ELISA cannot. The disease context (prostate cancer vs. AML) further limits direct comparisons.

Chakhachiro et al analyzed cellular CD105 expression in 85 AML cases using immunohistochemistry, reporting stronger expression in cases with specific cytogenetic abnormalities [e.g., t(15;17), t(8;21), t(6;9)].[16] Our study, with a smaller cohort and using ELISA, found no correlation with cytogenetic features. Immunohistochemistry to assess cellular expression in a larger sample likely accounts for these differences, as it may be more sensitive to cytogenetic-specific variations in CD105 expression compared with serum-based ELISA measurements.

Giorello et al studied 70 early invasive ductal breast cancer patients, using immunohistochemistry to measure CD105 expression in cancer-associated fibroblasts, finding higher levels associated with bone metastasis and shorter survival.[17] Mohamed et al examined 60 colorectal cancer patients, also using immunohistochemistry, and linked high CD105 levels to worse prognostic features.[18] In contrast, our study's use of ELISA in a smaller AML cohort (n = 30) found no such associations. The reliance on immunohistochemistry in these studies, which directly assesses tumor microenvironment expression versus our use of ELISA for soluble CD105, likely explains the differing results. Additionally, their larger sample sizes and solid tumor contexts may enhance the detection of prognostic signals not evident in our AML cohort.

A literature review reveals that endoglin (CD105) has been evaluated in many cancer types. Studies using immunophenotyping techniques have shown that endoglin (CD105) has prognostic significance. Since fewer studies use the ELISA method, specifically in AML patients, our study will contribute to the literature by providing additional insights into serum-soluble endoglin (CD105) levels in AML despite its limitations. The lack of significant results in our study, while potentially due to methodological differences (e.g., ELISA vs. immunohistochemistry), also suggests that soluble CD105 alone may not serve as a reliable prognostic or diagnostic biomarker in AML or that its role is more complex and influenced by other factors not assessed here.

To further elucidate the prognostic role of CD105 in AML, future research should focus on multicenter studies with larger sample sizes to enhance statistical power and generalizability across diverse patient populations. Combining ELISA for measuring soluble CD105 levels with immunohistochemistry to assess cellular expression in bone marrow or leukemic blasts could provide a more comprehensive understanding of CD105's biological and prognostic significance. Such studies should also better explore the interaction between CD105 and other angiogenic or molecular markers to define its potential as a biomarker in AML management.

 

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Conflict of Interest

None declared.

Compliance with Ethical Principles

The Atatürk University Faculty of Medicine Clinical Research Ethics Committee approved this study (Date: 02.06.2022, Decision no: 34).

Authors' Contributions

All authors contributed to collecting the data, writing the article, reviewing, and approving the final article.

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Publication History

Article published online:
22 July 2025