Myeloid Sarcoma: a Clinical Report of 18 Cases
Authors: Ye Xiujin , Zhu Lixia , Zhu Jinjin , Li Li , He Jingsong , Zhang Jie , Huang He 
Published: October 2019

Abstract
Abstract 4377

Background:
Myeloid Sarcoma (MS) is a rare neoplasm composed of immature myeloid cells occurring in any extramedullary organ most commonly in the skin, bone and lymph node. It may develop independently or concurrently with acute myeloid leukemia (AML), myeloproliferative disorder (MPD) or myelodysplastic syndrome (MDS). Some reports have described MS while most of them were one case report. In this study we retrospectively analyzed the clinical characteristics, treatment approaches and prognosis of 18 MS patients in our single center.

Methods:
between January 2003 and March 2010, eighteen MS patients were included in this study. The diagnosis depends on histological features and immunohistochemical results. All pathology specimens were routinely processed and examined by morphology. Immunohistochemical stains were performed on paraffin-embedded sections with monoclonal antibodies including MPO, CD3, CD20, CD79a, CD45, CD34, CD117, CD43. At the same time bone marrow aspiration were routinely examined. Disease morphology was determined according to the French-American – British(FAB) classification. After patients had comfirmed diagnosis with MS, they received cytarabine plus idarubicin or homoharringtonine for induction and consolidation chemotherapy. All the statistical analyses were performed using Kaplan-Meier.

Results:
among the 18 patients, the proportion of male and female was 1:1. Median age at diagnosis was 31.5 years (range 18–67). The usual involvement sites were skin (25%), lymph node (20%), breast (15%), uterus and cervix (15%). In total ten of the eighteen patients (55.6%) preceded AML without abnormality in peripheral blood and bone marrow while five patients concurrently developed AML-M2 and three (22.2%) were initially misdiagnosed as two were mistaken for Non-Hodgkin's lymphoma and the other for myeloma. In total 14 of 18 patients were examined by immunohistochemistry. The positive rate of MPO was 92.9% and other myeloid related markers were also strongly positive whereas lymphoid related markers were negative which were accord with biologic properties of myeloid cells. All the patients received chemotherapy. 10 patients without bone marrow involvement achieved complete disappearance of MS. Of these, 5 (50%) patients still kept complete remission after 1 year, 3 progressed to AML after six, eight and sixty-two months respectively; 2 died after two months after definite diagnoses of AML. As for the 6 patients with bone-marrow involvement undgone chemotherapy, 5 (83.3%) achieved complete bone-marrow remission but 3 of them relapsed at the points of seven,eleven and eighteen months, respectively. 4-year EFS and OS were longer in non-leukemic MS patients than in MS cases with bone-marrow involvement using Kaplan-Meier analyses.

Conclusion:
this study showed myeloid sarcoma could develop in various kinds of populations with easy misdiagnosis. Non-leukemic MS should be the beginning stage of AML. It is necessary to treat patients who have non-leukemic MS by classic chemical therapy for AML as early as possible. As such a study is limited by relatively small sample size, more clinical prospective trials in multiple centers should be carried out worldwide.

Disclosures:
No relevant conflicts of interest to declare.