What Is Myeloid Sarcoma?

Overview

Myeloid sarcoma is also known as chloroma; it is a type of blood cancer. It is a  solid tumour containing myelogenous cells ( a type of white blood cell) that occurs in the extramedullary site (skin, soft tissue, bones, lymph nodes and central nervous system).

Myeloid sarcoma is a rare cancerous tumour most commonly diagnosed in people with acute myeloid leukaemia (AML); unlike other blood cancers, including acute myeloid leukaemia, myeloid sarcoma forms outside the bone marrow. The bone marrow is the spongy tissue in the bones where the blood cells. These include white blood cells, red blood cells and platelets. Abnormal white blood cells (called myeloblasts) are formed in the bone marrow. These can spill out and travel through the bloodstream. 

Myeloid sarcoma occurs in extramedullary sites such as bone, muscle, fat, blood vessels, cartilage or other soft or connective tissues of the body, while other blood cancer forms in the bone marrow.

Causes and risk factors

Myeloid sarcoma forms when myeloid cells (cells that normally mature into healthy blood cells) become cancerous cells due to genetic mutations. Myeloblast cells(immature white blood cells) can enter the bloodstream, circulate and then the body’s tissues and organs and cause tumour formation. The myeloid sarcoma cells secrete cytokines (signalling molecules in the body), which help in the growth of the tumour. It is important to note that research is still ongoing to learn more about the cause of this condition.¹

Risk factors

 Depending on your previous medical history, you may be at risk of developing myeloid sarcomas. People who may be at risk include:

• The people suffering from acute myeloid leukaemia (AML): cancer seen in blood and bone marrow.
• People with chronic myeloid leukaemia (CML): a slowly progressing blood and bone marrow disease.
• People with myeloproliferative neoplasms: Myeloproliferative neoplasms cause increased blood cells.
• People with myelodysplastic syndrome:  Instead of immature blood cells maturing over time, with this condition, the immature blood cells do not mature, and there is a lack of healthy cells in the body.

Signs and symptoms

The signs and symptoms of myeloid sarcoma depend on the location and size of the tumour. These include:

• Extreme tiredness, including fatigue, whilst carrying out daily activities.
• Unexplained loss of weight despite having a balanced, healthy diet.
• Headache caused by extreme tiredness.
• Seizures and visual disturbances in cases of myeloid sarcomas affecting the skin.
• Myeloid sarcoma in the gastrointestinal tract can cause bowel obstruction and a loss of appetite.
• We localised mass or swelling at the affected site of the tumour.
• Skin lesions(known as chlormas) in cases of cutaneous myeloid sarcoma affecting the skin. 
• Pain, tenderness and weakness in the bones lead to fractures in myeloid sarcomas affecting the bones.

• Diagnosis There are different scans and tests that can be done to diagnose this condition. These tests include: 
  • CT scans can find any abnormalities in the body and also differentiate myeloid sarcoma from abscesses.²
  • MRI scans can find the abnormalities present in the body and identify tumours affecting the brain and spinal cord.
  • PET scans can find the exact location of the tumour and the number of tumours present.
  • Biopsywhere the cells, tissue or fluid are taken from the affected area for examination by the medical pathologist.
  • Cytogenetic analysis: This test helps identify damaged and abnormal chromosomes and myeloid sarcoma.
  • Immunophenotyping: This test helps in diagnosing and classifying the types of leukaemia or lymphoma.
  • In a bone marrow biopsy, the doctor takes a sample from the bone marrow in the pelvic bone, helping identify leukaemia.

Classification and staging

WHO classification

The World Health Organisation (WHO) classifies myeloid sarcoma as a subtype of acute myeloid leukaemia (AML). They are categorised into two types: 

1. Myeloid sarcoma associated with acute myeloid leukaemia: In this type, the cases of myeloid sarcoma occur with the acute myeloid sarcoma.
2. Myeloid sarcoma without the involvement of bone marrow: In this category, the myeloid sarcoma is isolated from the bone marrow, and there is no trace of leukaemia in the bone marrow or the blood.

Staging systems

The staging system is based on the development of the tumour and its severity and bone marrow disease. These stages include:

• Stage Ⅰ: These are isolated tumour masses only seen in the extramedullary site without the involvement of the bone marrow.
• Stage Ⅱ: More than one tumour is seen at different extramedullary sites without the involvement of the bone marrow.
• Stage Ⅲ: Myeloid sarcoma is present in the extramedullary site and is present in the bone marrow.
• Stage Ⅳ: Acute myeloid leukaemia is occurring with myeloid sarcoma in one or more extramedullary areas.
• Stage Ⅴ: Acute myeloid leukaemia occurs alongside extensive extramedullary tumours.

Prognostic factors

Prognostic factors are essential to understand as they help us identify the outcome of the disease and plan treatment. Some of these factors include:

• Cytogenetic and molecular markers: Where some specific mutations and chromosomal abnormalities can influence the behaviour of the disease and treatment.
• Extent of disease: The stages of the myeloid sarcoma always give a picture of the prognosis of the disease.
• Age: Younger healthy people affected by myeloid sarcoma have  better responses to the treatment than the elderly 
• Response to treatment: The response to the treatment helps to know the prognosis of the disease. The prognosis is different according to the area of the myeloid sarcoma affecting.

Treatment and management

Treatment for myeloid sarcoma and acute myeloid leukaemia are the same. Treatment is decided by considering various factors such as area of location of the tumour, size and number of tumours present, age and health of the patient, and the nature of the treatment. The oncologist (doctor treating cancer) may do a physical examination to determine the patient's health condition and will get a CT scan or MRI scan to determine the exact location of the tumour. The treatments are:  

Chemotherapy: 

Chemotherapy is a common cancer treatment where certain intravenous (through a vein) medications are given to destroy and prevent the growth of the tumour.³

Radiation therapy: 

Radiation therapy also known as radiotherapy, is a common treatment used in treating cancer cells independently or alongside chemotherapy and surgery. The types of radiation therapy are: 

• External beam radiation therapy (EBRT): In this procedure, a machine emits a direct beam of high-energy radiation towards the tumour. The energy emitted is x-rays, electrons or protons. During this procedure, the radiation targets the cancer cells specifically.
• Internal radiation therapy: Internal radiation therapy takes place inside the patient's body close to the cancer cells. It helps in treating smaller tumours situated in the head, neck, breast, cervix, uterus or prostate. The Internal radiation therapy types are:
  • Brachytherapy: In this procedure, a solid radioactive material is placed beside the tumour. That solid material releases radiation into the area and kills the cancer cells.
  • Systemic therapy: In this procedure, a radioactive material is sent through the blood to find the cancer cells and destroy them. The radioactive material is either in capsule form or injected intravenously (through a vein).⁵

Stem cell transplantation: 

Stem cells, which produce the blood cells, are present in the bone marrow. Some cancers are caused by abnormal blood cells. A stem cell transplant is the procedure where the stem cells are replaced with new stem cells, and healthy blood cells are produced. (HSCT).⁴

Targeted therapy:

Targeted therapy is a treatment that uses certain medicines designed to attack the cancer cells.

Surgery: 

Surgery is recommended to remove the tumour and helps prevent the nearby organs from being impacted by the tumour. Chemotherapy is usually combined with surgery.

Paediatric myeloid sarcoma

Paediatric myeloid sarcoma (paediatric granulocytic sarcoma) is a rare form of myeloid malignancy that occurs in children. There is infiltration of immature myeloid cells in the extramedullary area rather than the bone marrow.⁶

Prophylaxis and follow-up care

Prophylaxis and follow-up care are important components of cancer management, including myeloid paediatric sarcoma. This involves identifying high-risk patients and implementing targeted therapy or alternative treatment to reduce the risk of relapse. Regular follow-up care should be conducted to know the effect of the treatment, to monitor the recurrence of new tumours and lesions in the extramedullary site and to provide comprehensive support to the patient throughout their journey.

Novel therapies and ongoing research

Ongoing research and the development of novel therapies help in improving the understanding and treatment of myeloid sarcoma irrespective of all age groups. Some are: 

• Genomic profiling: This helps in identifying specific genetic mutations and chromosomal abnormalities related to the disease allowing proper treatment to be found.
• Precision medicine: Research is going on based on precision medicine where treatment is related to genetic mutation and characteristics of the tumour.
• Immunotherapy: These therapies are used to enhance the body’s immune response against the cancer cells.
• Epigenetic therapies:  These help in the alteration of gene mutations and inhibit tumour growth.
• Clinical trials: These are very important as they help in finding out the safety and efficiency of the new therapies.

FAQs

Who does the myeloid sarcoma affect?

Myeloid sarcoma can affect any person of any age and gender. It is commonly seen in adults with acute myeloid leukaemia and rare in people without acute myeloid sarcoma.

How common is myeloid sarcoma?

Myeloid sarcoma is a rare blood cancer, affecting from 2.5 % to 9.1% of people diagnosed with acute myeloid leukaemia.

Can myeloid sarcoma be cured?

Myeloid sarcoma is a rare and fast-growing cancer. If not treated, it can even lead to death. There isn’t a definitive cure; however, with treatment, the progression is delayed, allowing the patient to live longer.

Summary

Myeloid sarcoma is a rare cancerous tumour most commonly diagnosed in people with acute myeloid leukaemia (AML); unlike other blood cancers, including acute myeloid leukaemia, myeloid sarcoma forms outside the bone marrow. A solid tumour of the myelogenous cells (myelocytes, a type of white blood cell) occurs in the extramedullary site. Myeloid sarcoma is a fast-growing cancer which can progress quickly and can lead to death without proper treatment. However, studies have shown that with proper treatment the progression of myeloid sarcoma can be slow. A cure is difficult but it is possible depending on many factors, including the response of the body to the treatment. Research has shown that with the help of treatment, the patient can live longer with myeloid sarcoma.