Background: Myeloid sarcoma (MS) is a rare extramedullary tumour of immature myeloid cells developing de novo, constituting the first evidence of acute myeloid leukemia (AML) or as an initial sign of relapse in a previously treated AML. Myeloid sarcoma seldom occurs together with myeloproliferative neoplasm (MPN) or myelodysplastic syndrome (MDS). Because MS is a very rare condition, its precise clinical characteristics and established recommendations for therapy have not yet been formulated.
Objectives: A retrospective comparison of clinical characteristics and treatment outcomes in patients with isolated MS and AML patients without any proven extramedullary involvement - case control study.
Patients and methods: The case control study consisted of patients with MS and AML controls without proven extramedullary involvement treated at 8 Polish hematological tertiary care centers between January 1st 2001 and December 31st 2016.
Results: Subjectswere thirty nine MS patients of median age 44 years (range 18-70 years), with 24 (61.5%) males and 15 (38.5%) females. Of those with extramedullary involvement, there were 7 (18%) MS de novo, 4 (10%) secondary to MPN or MDS, 16 (41%) MS in AML relapse after chemotherapy and 12 (31% ) MS in AML relapse after allo-HSCT. The most often involved extramedullary sites were the central nervous system (18), soft tissues (8), lymph nodes (6), skin (6), bone (5), and pleura (4), with a mean of 1 site (range 1-4). In 21 (54%) patients, more than one site was infiltrated.
There were no differences between MS patients and controls in AML subtypes according to the WHO 2016 classification (p>0.05), except for AML with myelodysplasia-related changes which was more often diagnosed in the control group (23.1% vs 5.1%, p=0.007). Taking into consideration the previous AML classification (FAB classification) in the subgroup of MS patients with AML relapse after chemotherapy or allo-HSCT, nearly one third (28.5%), were classified as M4 or M5 subtype. The cytogenetic risk distribution according to the SWOG (ie. favorable, intermediate and poor) was similar in both groups (p=0.679). The elevated lactate dehydrogenase rate was lower in MS patients, 51.5% vs 83.3%, than in AML patients (p=0.046).
Upon establishing the diagnosis, systemic chemotherapy was administrated to over 90% patients in both groups. Additionally, radiotherapy was performed in 7 (18%) and surgical treatment in 2 (5.1% ) of the MS patients. Allo-HSCT was performed in 8 (20.5%) MS patients and 19 (48.7%) AML patients without extramedullary involvement (p=0.033).
The probability of a 1-year overall survival (OS) was significantly lower in patients with MS compared to AML patients without extramedullary involvement (66.1% vs 75.6%, p=0.031), similarly as was the relapse-free survival (RFS) (37.4% vs 75.8%, p<0.001) and the event-free survival (EFS) (48.4% vs 86.9%, p< 0.001) (Figure 1).
Conclusions: The prognosis in MS patients is poor, with significantly lower EFS, RFS and OS compared to AML patients without extramedullary involvement (Figure 1). New methods of treatment are thus urgently needed for such patients.
Warzocha: BMS: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau. Gora Tybor: Novartis: Honoraria, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau.
Asterisk with author names denotes non-ASH members.