Myeloid Sarcoma Preceding Clinically Recognized Acute Myeloid Leukemia in a Child: A Case Report
This case report describes a 7-year-old boy whose recurrent forearm mass, initially misdiagnosed as a hemangioma and lymphoblastic lymphoma, was ultimately identified as myeloid sarcoma preceding acute myeloid leukemia, highlighting the critical need for broad immunophenotyping and marrow correlation in pediatric soft-tissue lesions to ensure timely and effective treatment.
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Blood cancers often begin their journey inside the bone marrow, the spongy tissue deep within our bones where new blood cells are made. When this process goes wrong, immature cells called blasts can multiply uncontrollably, crowding out healthy cells and causing severe illness. Sometimes, these rogue cells do not stay confined to the marrow. They can break away and form solid lumps of tissue in other parts of the body, such as the skin, muscles, or organs. These lumps are known as myeloid sarcomas. While they look like tumors, they are actually made of the same blood cells that cause leukemia. This creates a difficult puzzle for doctors: if a child has a lump but no signs of leukemia in their blood, it is easy to mistake the mass for something else entirely, like a benign growth or a different type of cancer. Understanding how these solid tumors relate to the broader disease is crucial, because the treatment for a solid tumor of blood cells is very different from the treatment for a solid tumor of other tissues.
This story begins with a seven-year-old boy who arrived at a hospital in Iran with a fever, extreme weakness, and a painful swelling on his left forearm. His parents had noticed a small, hard area on his arm nearly eighteen months earlier. At that time, doctors used sound waves to look at the lump and saw structures that resembled blood vessels, leading them to believe it was a hemangioma, a common and usually harmless birthmark made of blood vessels. The boy's blood counts were mostly normal then, with only a slight drop in white blood cells, so no further invasive testing was done. Over the next year and a half, the lump grew slowly and became painful. When doctors finally removed a portion of it for examination, the cells looked like they belonged to a lymphoma, a cancer of the immune system, rather than a blood vessel tumor. Because the initial tests were limited, the medical team prepared to treat the boy for a lymphoid cancer, a plan that would have been entirely wrong.
The situation changed dramatically when the boy returned to the hospital with a high fever, widespread bleeding under the skin, and a rapid decline in his health. A new blood test revealed severe pancytopenia, meaning his body was producing almost no healthy red blood cells, white blood cells, or platelets. A sample taken from his bone marrow showed that forty percent of the cells were immature blasts, confirming a diagnosis of acute myeloid leukemia. However, the doctors did not stop there. They went back to the original tissue sample from the boy's arm and tested it again with a much wider set of markers to see exactly what kind of cells were present. This deeper look revealed that the cells in the arm lump were not lymphoma cells at all. They were weakly positive for myeloperoxidase, an enzyme found in myeloid cells, and expressed other markers consistent with myeloid leukemia. The lump in his arm was, in fact, a myeloid sarcoma that had appeared nearly two years before the leukemia became obvious in his blood.
Once the true nature of the disease was identified, the treatment plan shifted immediately to target acute myeloid leukemia. The boy received a combination of chemotherapy drugs designed to kill the myeloid blasts. Because the specific markers on his cells were not high enough to justify a different, more targeted drug, he received the standard induction therapy. The treatment worked quickly. After the first round of chemotherapy, the boy went into remission, and highly sensitive tests found no trace of the remaining disease in his body. This case highlights a critical lesson for medical care: when a child has a persistent or recurring soft-tissue mass that does not behave like a typical benign growth, doctors must look beyond the surface. A lump that appears to be a simple cyst or a lymph node could be the first sign of a blood cancer. By re-examining old tissue samples with a broader range of tests and connecting them to new findings in the bone marrow, doctors can avoid misdiagnosis and start the correct life-saving treatment sooner.
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