Low response rate to ATG-based immunosuppressive therapy in very severe aplastic anaemia - A Swedish nationwide cohort study.

OBJECTIVES: Antithymocyte globulin (ATG)-based immunosuppression remains a cornerstone in aplastic anaemia (AA) treatment. However, most ATG studies are not population-based and knowledge about real-world results concerning response and outcome could offer important information for treating physicians. METHODS: We have recently performed a nationwide retrospective cohort study on all AA patients diagnosed in Sweden in 2000-2011 and now present treatment and outcome data on patients receiving first-line ATG. In total, 158 patients showed a 47.0% response rate which was similar in all age groups (range 41.5%-51.7%) with no difference regarding ATG formulation. The response was significantly associated with severity grade-especially at time of treatment initiation: very severe (VSAA) 22.7%; severe (SAA) 54.5% (P < .001); and non-severe 88.5% (P < .001). A logistic regression-based predictive model indicated that VSAA patients with an absolute reticulocyte count <25 × 109 /L had only a 19% probability of response. In a multivariable analysis, age and VSAA at the time of treatment were the independent factors for inferior survival. CONCLUSIONS: Real-world VSAA patients respond poorly to ATG which indicates the need for a different treatment approach. Our findings suggest that age alone should not be a discriminating factor for administering ATG treatment.