What is the myeloid (bone marrow-related) system?

From the Guidelines

The myeloid system is a complex component of the human immune system, and its disorders, such as myelodysplastic syndromes, should be diagnosed and treated based on the most recent and highest quality guidelines, including the 2014 ESMO clinical practice guidelines for diagnosis, treatment, and follow-up 1. The myeloid system includes several types of white blood cells, such as neutrophils, monocytes, macrophages, dendritic cells, eosinophils, and basophils, as well as platelets and red blood cells. These cells play essential roles in defending the body against infections, particularly bacterial and fungal pathogens, through processes like phagocytosis, inflammation, and antigen presentation. Some key points to consider when diagnosing and treating myeloid system disorders include:

• The WHO classification of myelodysplastic syndromes, which includes refractory cytopenia with unilineage dysplasia, refractory anemia with ring sideroblasts, refractory cytopenia with multilineage dysplasia, and refractory anemia with excess blasts 1.
• The importance of cytogenetic abnormalities in diagnosing and subclassifying myelodysplastic syndromes, including the use of flow cytometry to detect phenotypic abnormalities 1.
• The need for careful monitoring and follow-up of patients with myeloid system disorders, including regular blood counts and bone marrow examinations, to detect any changes in the disease course or response to treatment 1.
• The use of treatment protocols, such as hypomethylating agents, chemotherapy, and allogeneic stem cell transplantation, to manage myeloid system disorders, including myelodysplastic syndromes and acute myeloid leukemia 1. In terms of treatment, the 2014 ESMO guidelines recommend that treatment for myelodysplastic syndromes should aim to modify the natural disease course, including the use of hypomethylating agents, chemotherapy, and allogeneic stem cell transplantation, whenever possible 1.

From the FDA Drug Label

The overall response rate (CR + PR) of 15.7% in azacitidine for injection-treated patients without AML Response occurred in all MDS subtypes as well as in patients with adjudicated baseline diagnosis of AML. Patients responding to azacitidine for injection had a decrease in bone marrow blasts percentage, or an increase in platelets, hemoglobin or WBC The mean and median duration of clinical response of PR or better was estimated as 512 and 330 days, respectively; 75% of the responding patients were still in PR or better at completion of treatment

The myeloid system is affected by azacitidine, as evidenced by the decrease in bone marrow blasts percentage and the increase in platelets, hemoglobin, or WBC in responding patients 2.

• Key effects on the myeloid system include:
  • Decrease in bone marrow blasts percentage
  • Increase in platelets, hemoglobin, or WBC
• Response rates were seen in all MDS subtypes, as well as in patients with adjudicated baseline diagnosis of AML.

From the Research

Myeloid System Overview

• The myeloid system is a complex network of cells and tissues responsible for the production of blood cells, including red blood cells, white blood cells, and platelets.
• Myeloid disorders, such as acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), can arise from abnormalities in the myeloid system.

Treatment of Myeloid Disorders

• Azacitidine (AZA) and donor lymphocyte infusions (DLI) have been used as a salvage treatment for AML and MDS relapsing after allogeneic hematopoietic stem cell transplantation (HSCT) 3, 4, 5.
• The combination of AZA and DLI has shown promising results, with overall response rates ranging from 33% to 56% and complete remission rates ranging from 25% to 38% 3, 4, 5.
• The addition of lenalidomide to AZA and DLI has also been investigated, with preliminary results suggesting improved efficacy and tolerability 4.

Prognostic Factors and Risk Stratification

• Molecular-only relapse, diagnosis of MDS, and low disease burden have been identified as predictors of complete remission and better overall survival in patients with myeloid disorders 3, 5.
• The Revised International Prognostic Scoring System (IPSS-R) is a commonly used scoring system for risk stratification in MDS, taking into account factors such as peripheral cytopenias, percentage of blasts in the bone marrow, and cytogenetic characteristics 6.

Emerging Therapies and Future Directions

• Novel therapeutics, such as luspatercept and oral hypomethylating agents, have been approved for the treatment of MDS, offering new options for patients with progressive or refractory disease 6.
• Ongoing studies are investigating the use of targeted therapies, maintenance therapy, and post-transplant strategies to mitigate relapse risk and improve outcomes in patients with AML and MDS 7.