INTESTINAL PRIMARY MYELOID SARCOMA AS AN ISOLATED PRESENTATION WITHOUT BONE MARROW INVOLVEMENT: CASE REPORT AND NARRATIVE REVIEW.

Myeloid sarcoma (MS) is a rare extramedullary manifestation of immature myeloid cell proliferation, and its occurrence preceding acute myeloid leukemia (AML) is uncommon. MS can affect several organs and tissues, as the infiltration of gastrointestinal (GI) tract being particularly rare. A standard treatment for isolated MS has not yet been established; however, due to the high risk of progression to AML, intensive chemotherapy is generally recommended and may be combined with allogeneic stem cell transplantation (allo-SCT), radiotherapy (RDT), and surgery. Therefore, this study aims to report a case of an isolated MS and compare it with what is available in the literature as a narrative review. We conducted a review of similar cases of MS published in the last 10 years by searching the PUBMED database. Our search identified 28 articles, 18 of which were included in this review. Results: (1) Case report: a 35-year-old male presented with lower abdominal pain associated with alternating episodes of diarrhea and constipation in January 2024. In April, he was hospitalized due to an intestinal obstruction, as the abdominal CT scan revealed a small intestine wall obstruction mass by the mesogastric region. He underwent emergency enterectomy with the resected material consistent with MS by immunohistochemistry (IHC): positive for MPO, CD71, CD34, c- KIT; negative for CD61. The patient was kept without any other intervention until his first consultation at our service in May 2024. His blood counts showed no alterations, and a bone marrow biopsy revealed no signs of infiltration. PET-CT demonstrated an area of abnormal uptake (SUV max of 7.3) in the pelvic region corresponding to a heterogeneous pre-sacral mass. He underwent a CT guided biopsy that confirmed the persistence of the MS. The patient started induction chemotherapy in May 2024 with daunorubicin and cytarabine (3+7), achieving a complete remission (CR) by the PET-CT performed in June 2024. The patient followed treatment with 4 cycles of consolidation with high dose cytarabine until October 2024 and additionally, he underwent RDT with 24 Gy in December 2024. A new PET-CT was performed in January 2025 still maintaining CR. (2) In our literature review, 18 cases of primary gastrointestinal MS were identified. The male-to-female ratio was 2:1, and the mean age was 45 years. The most affected site in the GI tract was the small intestine (50% of cases). IHC showed positivity for MPO, CD34, and CD117 in nearly all cases, along with high Ki-67 indices ranging from 30% to 95%. Most patients responded well to intensive chemotherapy regimens based on cytarabine and anthracyclines, with or without allo-SCT (only 3 paients underwent consolidation with all- SCT), whereas surgical treatment alone was insufficient for disease control. MS is a rare entity with a challenging diagnosis and no established standard of care. A transplant-free approach may be viable depending on patient-specific factors, with sustained complete responses achieved through chemotherapy and radiotherapy alone. Understanding the complex interplay of genetic, environmental, and immunological factors in the pathogenesis of isolated MS is essential to identifying effective treatment strategies and improving patient outcomes.