Hematologic malignancies The myeloid stem cell disorders include acute
myeloid leukemias, as well as myeloproliferative and myelodysplastic disorders.
These three groups overlap one another, as they share common features in their development.
In the following, we will explain the differences between these three groups.
Acute leukemias are malignant neoplasms in the classical sense,
that is, one malignant cell forms numerous malignant cells and there is no maturation.
This creates a cell clone of uniform, nonfunctional cells, which are termed as blasts.
In more simple terms the following can be said about leukemias:
First, the cell division rate is increased in leukemia, so there are generally quantitatively
more cells present.
Second, there is no further cell maturation, therefore cell quality or function is limited.
For example, a single myeloblast gives rise to many more myeloblasts in the bone marrow.
Let’s compare the myeloproliferative neoplasms with the malignant neoplasms.
In myeloproliferative neoplasms, there is an overproduction of cells in the bone marrow.
In other terms, the cell proliferation rate is increased and more cells are present.
However, the cells follow their normal differentiation course.
Let’s use neutrophils as an example.
The myeloblast divides rapidly, but still develops through its intermediate forms to
mature granulocytes.
Like the leukemias, there are quantitatively more cells present, however, maturation continues.
Therefore, the quality or function of the cells is not limited.
During the course of disease, further mutations may arise, which affect cell differentiation
and thereby cell function.
This so-called maturation arrest leads to a more aggressive disease and eventual progression
to acute myeloid leukemia.
Finally, we would like to introduce the myelodysplastic syndromes.
They are not characterized by the overproduction of cells in the bone marrow, but by bone marrow
dysfunction.
In myelodysplastic syndromes, there is a genetic alteration in the stem cells, which is associated
with an increase in cell numbers in the bone marrow.
This genetic alteration is rather evident, as the affected cells are damaged and thereby
limited in their form and function.
Hence, the term myelodysplastic syndrome.
But as a consequence of the dysplasia, fewer mature cells leave the bone marrow, which
leads to a decrease in the number of functional cells in blood.
To compare the myelodysplastic syndromes with the other two groups, the cells in the bone
marrow are quantitatively increased, but are, however, dysplastic and therefore decreased
in blood.
Furthermore, cell quality is also reduced.
This description in the form of quantity and quality is merely for simplification purposes
and only refers to the onset of disease.
As previously mentioned, the myeloproliferative and myelodysplastic disorders can transition
to acute myeloid leukemias over the course of disease.
There is also a mixed form of both disorders, which is termed myelodysplastic/myeloproliferative
neoplasms.
They possess features of both myeloproliferation and myelodysplasia.
In other words: There is an evident increase of at least one cell line in the peripheral
blood count and dysmyelopoiesis in the bone marrow.
But you don’t need to memorize all of these details, as it delves into advanced hematology;
it merely serves to underline which principles may apply during classification.
Namely, myeloproliferation and myelodysplasia may occur separately, such as in the previous
groups, but that both of these changes may also occur simultaneously, as shown in this
group.
The slash in the name of this group is somewhat confusing as it does not refer to either,
but to a disorder that demonstrates characteristics of both.
So now onto the clinical presentation of myeloproliferative neoplasms.
The symptoms of myeloproliferative neoplasms depend on which cell line is respectively
increased.
For example, an increase in red blood cells leads to hyperemia, which is termed as plethora.
Plethora is manifested by excessive facial redness.
If platelet numbers are elevated, the risk of thrombosis also increases.
The third cell line that may be increased is the granulocyte cell line, whereby neutrophils
are primarily affected.
Interestingly, an increase in the number of functional granulocytes in blood does not
initially result in any clinical symptoms.
However, a drastic increase in cell numbers may result in leukemic cellular thrombi.
So now onto the symptoms of the myelodysplastic syndromes.
At the forefront of myelodysplastic syndromes lies the reduction of the cell lines and not
an increase.
Erythropoiesis is usually affected resulting in anemia.
However, two or three cell lines may be simultaneously affected, leading to a bleeding tendency and
susceptibility to infection.
Finally, we move onto the symptoms of the acute myeloid leukemias.
They are based on the suppression of blood-forming cells in the bone marrow via blasts.
Acute myeloid leukemias can therefore have similar symptoms to myelodysplastic syndromes,
in which one or more cell lines are reduced.
Myelodysplastic syndromes, however, occur in individuals of older age and have a slow
course, often over several years.
But don’t worry, even if this initially sounds somewhat confusing, it is quite easy
in the end.
The key to differentiating between the three groups is ultimately based on the “hematological
presentation”, that is, which cells are altered in the bone marrow and blood.
We would like to briefly summarize this mountain of information.
There are two major cell lines, namely the myeloid and lymphoid cell lines.
The acute lymphoblastic leukemias and the lymphomas belong to the lymphatic disorders.
Myeloid disorders comprise of acute myeloid leukemias as well as the myeloproliferative
and myelodysplastic disorders.
The various disorders are based on the malignant transformation of different blood cells.
Clinical symptoms depend on the type of blood cell affected and whether there is an impaired
proliferation rate, impaired differentiation, or both.
Acute lymphoblastic leukemias and acute myeloid leukemias are often grouped together under
the term acute leukemias.
We have not yet touched on the chronic leukemias.
This is because they do not have their own group.
On the contrary, the chronic leukemias hold a special position.
As we will see, chronic lymphocytic leukemia is assigned to the lymphomas and chronic myeloid
leukemia belongs to the myeloproliferative neoplasms.