Successful treatment with gilteritinib for popliteal extramedullary relapse of FLT-3-ITD acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation : a case report and literature review
This case report demonstrates that gilteritinib monotherapy successfully induced and maintained a durable complete remission in a 63-year-old patient with FLT3-ITD-positive myeloid sarcoma relapsing as an isolated popliteal mass six years after allogeneic hematopoietic stem cell transplantation, offering a viable treatment alternative for patients ineligible for intensive chemotherapy or donor lymphocyte infusion.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Cancer is a disease of cells that have lost their ability to stop growing, but in some forms of blood cancer, the problem is even more specific. Imagine the body's blood-making factory, located in the bone marrow, as a place where new cells are constantly being built. In a type of cancer called acute myeloid leukemia, this factory starts producing defective cells that crowd out the healthy ones. Sometimes, these rogue cells do not stay inside the factory; they travel through the bloodstream and set up new, dangerous colonies in other parts of the body, such as the skin, lymph nodes, or joints. This is known as an extramedullary relapse, or a relapse outside the marrow. For patients who have already undergone a stem cell transplant—a procedure where a healthy donor's blood-making system replaces the patient's own—the return of cancer is particularly difficult to treat. The standard tools, like strong chemotherapy, are often too harsh for patients who are older or have other health issues, and the immune system from the donor may not be strong enough to fight the cancer on its own. In these complex situations, doctors need new ways to target the cancer without destroying the patient.
This story begins with a man in his sixties who had been living with a chronic blood disorder for many years. His condition eventually changed into acute myeloid leukemia, a more aggressive form of the disease. After receiving intensive chemotherapy to clear the cancer, he underwent a stem cell transplant from an unrelated donor. For six years, the treatment worked perfectly. He had no signs of cancer, and his blood was being made entirely by the donor's cells. However, in 2023, he returned to the hospital with a painful swelling behind his left knee. Medical scans revealed a large mass, nearly nine centimeters wide, growing in the space behind the knee joint. A biopsy confirmed that this was not a simple injury or infection, but a return of his leukemia, specifically a tumor made of myeloid cells known as a myeloid sarcoma.
The situation was complicated. When doctors examined the patient's bone marrow, they found very few cancer cells there, but they did detect a specific genetic change called an FLT3 mutation in the marrow. This mutation acts like a stuck switch, telling the cancer cells to grow uncontrollably. The tumor behind the knee was the main problem, but the patient was seventy-five years old and had other health conditions, including a chronic reaction to the donor cells that had left his skin scarred. Because of his age and health, the standard approach of using powerful chemotherapy or infusing more donor immune cells was not safe for him. The medical team needed a treatment that could target the cancer directly without overwhelming his body.
They chose a medication called gilteritinib, a drug designed specifically to block the FLT3 mutation. The patient began taking a daily dose of 120 milligrams. This drug works by cutting off the signal that tells the cancer cells to multiply. To help clear the large mass behind the knee, doctors also applied targeted radiation therapy to that specific area. The results were rapid and significant. Within three months, the large tumor had shrunk dramatically, and the patient's pain and swelling disappeared. Scans showed that the mass had lost almost all of its metabolic activity, meaning the cells inside were no longer active. A follow-up examination of his bone marrow showed that the cancer cells were gone, the genetic mutation was no longer detectable, and the donor cells had once again taken over nearly all of his blood production.
The treatment was gentle on the patient. He experienced only a temporary rise in liver enzymes, which returned to normal without needing to stop the medication or lower the dose. Two years after the cancer first returned, the patient remained in complete remission. He had normal blood counts, no signs of the tumor, and his chronic health issues remained stable. This case demonstrates that for patients who cannot tolerate aggressive treatments, a targeted drug like gilteritinib can successfully clear cancer that has returned outside the bone marrow. It suggests that even when the cancer hides in a specific spot like the knee, blocking the genetic switch that drives it can lead to a lasting cure. The success of this treatment also highlights the importance of testing for genetic mutations in these tumors, even if the patient did not have them before, because the cancer can change its nature after a transplant.
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