Blood, 15 November 2000, Vol. 96, No. 10, pp. 3656-3659
CORRESPONDENCE
To the editor:
Angiogenesis in acute myeloid leukemia
We have read with interest the report of Padrò et
al1 showing an increased angiogenesis in acute myeloid
leukemia. Recently, other studies published in Blood also
have shown that angiogenesis in acute myeloid leukemias is higher than
in controls2 and that it has an independent prognostic
significance.3 But measurement of angiogenesis in
hematology is still in its infancy, and a consensus on the methodology
and criteria of evaluation is still lacking. Some methods employed in
solid tumors such as CD34 or CD31 immunostaining cannot be used because
of the positivity of leukemic cells for these antigens. In the
aforementioned papers, the increase of angiogenesis has been
demonstrated by using endothelial cell markers such as
immunohistochemistry for von Willebrand factor and
thrombomodulin1 or a monoclonal antibody against
endothelial cells (ULEX-E2) or by measuring vascular
endothelial growth factor (VEGF3), which is considered the
most important soluble mediator of angiogenesis4 and
correlates with microvessel density.5 On the one hand, the
common finding of an increased angiogenesis by using different methods
of measurement validates the results of each report. On the other hand,
however, the disparity of the methods indicates the necessity for more
precise rules in the evaluation of angiogenesis in
hematological diseases.
In this regard, it is well known that, in normal conditions,
angiogenesis may be driven by hypoxia. VEGF may be released by virtually all normal cells and several neoplastic cell lines in response to hypoxia.4 Therefore, it is possible that in
some anemic patients angiogenesis is increased at least in part for the
anemia-related hypoxia. This possible correlation between anemia and
angiogenesis is not taken into account in any of the aforementioned
papers, although anemia is a common symptom in acute leukemias. Because
the hypoxic regulation of VEGF is mediated by the hypoxia-inducible
factor 1 (HIF-1) with a mechanism similar to the hypoxic regulation of
erythropoietin (Epo),6 it is possible to use serum Epo
concentration (which correlates with the hypoxic stimulus) as an
indirect measurement of the amount of hypoxia-related angiogenesis in
each patient.
This argument applies also to controls. We think that anemic
patients should not be used as controls in evaluation of angiogenesis because of a possible increase of hypoxia-induced VEGF. In contrast, Padrò and colleagues'1 control patients included
some lymphoma and other "nonmalignant disorders," and Hussong and
colleagues'2 controls included patients with
"cytopenias." Although hemoglobin levels were not reported, it is
possible that some of these subjects were anemic, which would
at least partly explain the increase of angiogenesis observed in some
control patients.
Actually, we have studied the VEGF levels in 2 other
hematological malignancies, multiple myeloma7 and
idiopathic myelofibrosis,8 and have found that in both
diseases there is an increase of circulating VEGF concentrations (and
therefore of angiogenesis) that is not correlated with serum Epo
levels. In the same patients, Epo levels correlate with anemia. We
concluded that in these diseases angiogenesis is increased per se and
not as a consequence of anemia.
We are convinced that the same could happen in AML, and the data
presented by the various authors1-3 are really indicative of a true increase of angiogenesis in acute leukemias. But we think
that the simple measurement of serum Epo levels should be included in
the evaluation of angiogenesis in all of the diseases where anemia is a
common symptom.
Francesco Di Raimondo, Giuseppe A. Palumbo, Maria Pia Azzaro, and Rosario Giustolisi
University of Catania Catania, Italy
References
1.
Padrò T, Ruiz S, Bieker R, et al.
Increased angiogenesis in the bone marrow of patients with acute myeloid leukemia.
Blood.
2000;95:2637-2644[Abstract/Free Full Text].
2.
Hussong JW, Rodgers GM, Shami PJ.
Evidence of increased angiogenesis in patients with acute myeloid leukemia.
Blood.
2000;95:309-313[Abstract/Free Full Text].
3.
Aguayo A, Estey E, Kantarjian H, et al.
Cellular vascular endothelial growth factor is a predictor of outcome in patients with acute myeloid leukemia.
Blood.
1999;94:3717-3721[Abstract/Free Full Text].
4.
Ferrara N, Davis-Smyth T.
Biology of vascular endothelial growth factor.
Endocr Rev.
1997;18:4-25[Abstract/Free Full Text].
5.
Mattern J, Koomagi R, Volm M.
Association of vascular endothelial growth factor expression with intratumoral microvessel density and tumor cell proliferation in human epidermoid lung carcinoma.
Br J Cancer.
1996;73:931-934[Medline]
[Order article via Infotrieve].
6.
Goldberg MA, Schneider TJ.
Similarities between the oxygen-sensing mechanisms regulating the expression of vascular endothelial growth factor and erythropoietin.
J Biol Chem.
1994;269:4355-4361[Abstract/Free Full Text].
7.
Di Raimondo F, Azzaro MP, Palumbo GA, et al.
Angiogenic factors (VEGF, bFGF, and HGF) in multiple myeloma: higher levels in bone marrow than in peripheral blood.
Haematologica.
2000;85:800-805[Abstract/Free Full Text].
8.
Di Raimondo F, Azzaro MP, Palumbo GA, et al.
Elevated VEGF serum levels in idiophatic myelofibrosis.
Blood.
1999;94 (suppl 1):509a.
Response:
Angiogenesis and anemia in acute myeloid leukemia
Dr Di Raimondo and colleagues are concerned about the
standardization of the methodology for evaluating angiogenesis in
hematological diseases. We fully agree with them that standardization
of angiogenesis quantification is desirable to yield reliable results.
Thus results obtained at different institutes would be comparable and
allow for meta-analyses. But the assessment of angiogenesis by
determination of microvessel density as performed in our
study1 is a modification of a well-established
method2 and an international consensus report.3 To ensure the reliability and reproducibility of
this quantification method in acute myeloid leukemia (AML), we adhered to a strict protocol for selection of hot spots and introduced several
internal controls.1 Thus, our investigation has
unequivocally demonstrated a significant increase of bone marrow
microvessel density in AML.
As Di Raimondo et al correctly point out, the common finding of
increased angiogenesis in AML patients in spite of different methods
(thrombomodulin/von Willebrand factor staining in our study1 and von Willebrand factor/ULEX-E staining in the
study by Hussong et al4) underscores the validity of
the results obtained in AML. But Di Raimondo and colleagues' statement
that angiogenesis is an independent prognostic factor in AML is not justified. The cited report of Aguayo et al5 has shown
that cellular vascular endothelial growth factor (VEGF), a potent
angiogenic factor, is an independent predictor of outcome in AML. But
neither data on bone marrow microvessel density nor on correlations of VEGF levels with microvessel density were provided in this study. Thus,
in AML the prognostic value of increased angiogenesis has yet to be demonstrated.
Of course, anemia is a common symptom in newly diagnosed, untreated AML
patients, and it has been demonstrated that hypoxia up-regulates VEGF
expression in both normal and malignant cells.6 Accordingly, anemia might contribute to increased bone marrow angiogenesis by aggravating tissue hypoxia. But it is unlikely that the
induction of known growth factors for endothelial cells such as VEGF
alone is sufficient to induce the angiogenic switch. Therefore,
defining more carefully the genes that are in situ up-regulated or
down-regulated under hypoxic conditions in AML will be more important
than correlating angiogenesis with serum erythropoietin (Epo) levels as
a surrogate for tissue hypoxia. Furthermore, factors other than tissue
hypoxia have been suggested to be involved in the regulation of Epo
production and influence serum concentrations.7 For
example, serum Epo levels have been found to be variable for a given
hemoglobin concentration in patients with myelodysplasia.8
In patients with untreated acute leukemia, Epo levels have been
reported to be higher than in controls and have continued to increase
following chemotherapy.9 When assuming that serum Epo
concentrations positively correlate with hypoxia-related angiogenesis
in AML, it is difficult to reconcile this Epo increase with our
observation of a significant decrease in bone marrow microvessel
density following chemotherapy.1
Indeed, the control patients in our study had lower hemoglobin
levels than a healthy population (median [interquartile range], 11.4 [10.8-13.4]). Therefore, we cannot exclude that tissue hypoxia might
have caused slightly increased angiogenesis in our control population.
If this was the case, however, differences between AML and control
patients would be underestimated rather than overestimated in our
study. Yet we found no correlation between hemoglobin levels and bone
marrow microvessel density within the control group
(r = -0.123; assessed by the Pearson coefficient).
Therefore, we disagree with Dr Di Raimondo and colleagues that serum
Epo levels are important for the interpretation of our findings.
Teresa Padró, Wolfgang E. Berdel, Thomas Büchner, and Rolf M. Mesters
Department of Medicine/Hematology and Oncology University of
Muenster Muenster, Germany
References
1.
Padró T, Ruiz S, Bieker R, et al.
Increased angiogenesis in the bone marrow of patients with acute myeloid leukemia.
Blood.
2000;95:2637-2644.
2.
Weidner N, Semple JP, Welch WR, Folkman J.
Tumor angiogenesis and metastasis - correlation in invasive breast carcinoma.
N Engl J Med.
1991;324:1-8[Abstract].
3.
Vermeulen PB, Gasparini G, Fox SB, et al.
Quantification of angiogenesis in solid tumors: an international consensus on the methodology and criteria of evaluation.
Eur J Cancer.
1996;32A:2474-2484.
4.
Hussong JW, Rodgers GM, Shami PJ.
Evidence of increased angiogenesis in patients with acute myeloid leukemia.
Blood.
2000;95:309-313.
5.
Aguayo A, Estey E, Kantarjian H, et al.
Cellular vascular endothelial growth factor is a predictor of outcome in patients with acute myeloid leukemia.
Blood.
1999;94:3717-3721.
6.
Minchenko A, Bauer T, Salceda S, Caro J.
Hypoxic stimulation of vascular endothelial growth factor expression in vivo and in vitro.
Lab Invest.
1994;71:374-379[Medline]
[Order article via Infotrieve].
7.
Cazzola M, Mercuriali F, Brugnara C.
Use of recombinant human erythropoietin outside the setting of uremia.
Blood.
1997;89:4248-4267[Free Full Text].
8.
Bowen DT, Culligan D, Beguin Y, Kendall R, Willis N.
Estimation of effective and total erythropoiesis in myelodysplasia using serum transferrin receptor and erythropoietin concentrations, with automated reticulocyte parameters.
Leukemia.
1994;8:151-155[Medline]
[Order article via Infotrieve].
9.
Aydogdu I, Ilhan O, Beksac M, et al.
Serum erythropoietin levels in patients with leukemia on cytostatic treatment.
Haematologia.
1998;29:133-137[Medline]
[Order article via Infotrieve].
