Luspatercept in MDS with Ring Sideroblasts: A Real-Life Multicenter Experience from a Named Patient Program

Background

Low risk Myelodysplastic syndromes (LR MDS) are a heterogeneous group of clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis, peripheral cytopenias and relative increase of bone marrow blasts [List 2004]. The most common cytopenia is anemia, which occurs in 85-90% of cases (isolated in 35% of cases) [Fenaux 2013], and ranges from mild/asymptomatic to transfusion dependent. The standard of care for anemia remains supportive care and about 70% of cases benefits from erythropoiesis-stimulating agents (ESAs).

According to the FAB classification, a low-risk group of MDS characterized by the presence of ring sideroblasts (RS) was recognized. In the 2017 WHO classification, the nosologic entities of MDS uni-linear and multi-linear dysplasia with RS (MDS-UD-RS, MDS-MD-RS) were established, to emphasize the importance of identifying forms with a potential therapeutic target [Arber 2016].

Luspatercept is a recombinant fusion protein consisting of the modified extracellular domain of human activin receptor type IIB (ActRIIB) linked to a domain of human immunoglobulin Fc G1. The drug showed efficacy in re-establishing erythropoiesis and was recently approved for the treatment of adult patients with very low- to intermediate-risk MDS-RS failing ESAs[Platzbecker 2017; Fenaux 2020].

Aims

To retrospectively assess the efficacy and/or clinical benefit (defined as a reduction in red blood cells transfusions [RBCT] or increase in hemoglobin levels) of luspatercept in patients with LR MDS with RS in a real-life setting. Safety issues were also addressed and clinical and hematological predictors of outcome analyzed.

Methods

We considered all IPSS-R lower-risk MDS with RS patients with unsatisfactory response or unsuitable for ESAs, treated with luspatercept as monotherapy through an expanded access program since November 2020, in 2 tertiary hematologic centers in Milan, Italy. Luspatercept was administered according to the published schedule: starting dose 1,0 mg/kg every three weeks, with the possibility to increase up to 1,33 mg/kg and 1,75 mg/kg if patients did not reach transfusion independence or decreased transfusion burden after two consecutive infusions. Response to luspatercept was evaluated according to IWG 2018 criteria: Hb increase by > 1.5 g/dL and/or relevant reduction of units of RBC transfusions by an absolute number of at least 4 RBC transfusions/8 wk compared with the pretreatment transfusion number in the previous 8 wk.

Results

We included a total of 17 pts (70% males, 30% females), with a median age of 68 years (range 45-89). The median follow-up from the start of the Luspatercept was 4 months (range 3-6).According to WHO 2017 we included 13 MLD (76%) and 4 ULD (24%); in all of them SF3B1 mutations was confirmed. Moreover, According to IPSS-R classification: 5 (27%)cases were intermediate and 12 (73%) low risk.

All patients received at least three doses of luspatercept. Nine patients (53%) needed a dose escalation to 1,33 mg/kg, and 7 (41%) required the maximal dose of 1,75 mg/kg. Interestingly, not all patients received a dose escalation, and 8 (47%) obtained prolonged efficacy with 1 mg/kg dose.

Hemoglobin levels increased in 9 pts (53%): 4 (24%), 3 (18%) and 2 (12%) cases at 1 mg/Kg, 1,33 mg/kg and 1,75 mg/dl, respectively. Medina increase was 1,5 g/dl (range 0,2 - 2,2) and these levels were maintained for a median of 4 months (range 3-6).

In addition, considering transfusion burden, the independence was reached in 3 pts (18%), after a median time of 6 weeks from treatment start. Importantly, off the 14 patients remaining transfusion-dependent, 6 (35%) reduced the transfusion burden.

The most prominent toxicity was increased blood pressure (grade 2) occurring in 3 pts (18%), and dizziness (grade 2) in 2 pts (12%); though the drug was generally well tolerated. No serious adverse events (SAEs) were reported. Therefore, patients were treated as outpatients in all cases.

At the last follow up, all patients are alive and free from leukemic evolution.

Conclusions:

Our real-world experience confirms the efficacy of luspatercept in improving erythropoiesis and decreasing transfusion dependency in very low, low or intermediate risk MDS with RS, with an acceptable toxicity profile.