Identification of Adverse Risk Factors for Survival in Acquired Pure Red Cell Aplasia Receiving Immunosuppressive Therapy By the Japan PRCA2004/2006 Study and Introduction to the New Cohort Study PRCA2016

Pure red cell aplasia (PRCA) is characterized by normocytic normochromic anemia associated with reticulocytopenia and erythroid hypoplasia in otherwise normal bone marrow. The acquired chronic PRCA may present as a primary hematological disorder in the absence of any other diseases or develop associated with certain conditions such as thymoma, lymphoproliferative disorders, infections, collagen vascular diseases, or after exposure to a wide variety of drugs. Idiopathic PRCA and secondary PRCA not responding to the treatment of the underlying diseases are generally treated by immunosuppressive therapy and the most patients require long-term treatment. Glucocorticoids, cyclosporine and cyclophosphamide are commonly used for initial treatment as monotherapy or combination therapy and majority of the patients respond to immunosuppression. However, most patients treated with these medications relapse during tapering of the treatment. Because of the extreme rarity of this disease, the long-term outcome of chronic PRCA following immunosuppression remains unclear and the adverse risk factors for survival have to be elucidated.

In order to identify the adverse risk factors for survival in acquired chronic PRCA following immunosuppression and improve the prognosis, we have conducted nationwide surveys for adult acquired chronic PRCA in Japan. We conducted the first study for adult chronic PRCA in japan in 2004 and 2006 that had been diagnosed between 1990 and 2006 across 109 institutions, and collected the data on a total of 185 patients (PRCA2004/2006 study). We have also started another cohort study in 2016 in collaboration with the Japanese Society of Hematology (JSH) (PRCA2016 study) that was approved by the institutional review board and the ethical committee of the JSH.

In PRCA2004/2006 study 73 patients (39%) were classified as having idiopathic PRCA and 112 patients (61%) as having secondary PRCA, including 42 thymoma- and 14 large granular lymphocyte leukemia (LGL)-associated PRCA. The details on idiopathic, thymoma-associated and LGL-leukemia-associated PRCA have been previously reported (Sawada K, et al. Haematologica 2007;92:1021; Hirokawa M, et al. Haematologica 2008;93:27; Fujishima N, et al. Haematologica 2008;93:1555). The last questionnaires for the patients with these three subtypes of PRCA were sent to the institutions in 2012 for collecting the data on relapse, subsequent treatment and efficacy and outcome.

The PRCA2004/2006 study revealed that the median overall survival (OS) has not yet been reached in idiopathic PRCA following immunosuppression and the estimated median OS times in thymoma-associated and LGL leukemia-associated PRCA were 142 and 148 months, respectively. Twenty-two deaths were reported and the major causes of death were infection and organ failure (Hirokawa M, et al. Brit J Haematol 2015;169:879). Poor response to induction therapy and relapse of anemia were demonstrated to be associated with death and this was also confirmed by the Mantel-Byar analysis (p<0.001)　(Fig. 1). The efficacy of re-induction therapy for relapsing PRCA was inferior to the initial inductive therapy (p<0.001) (Fig. 2).

With the results of this study, we have proposed the clinical guidelines for management of PRCA in 2011 and we conducted another cohort study in 2016 in collaboration with the Japanese Society of Hematology (JSH) (PRCA2016 study). The primary endpoint of this study is the OS in chronic PRCA following immunosuppression and the principal aim is to learn whether or not the prognosis would be improved. Between 2006 and 2014, 554 PRCA patients were registered in the JSH hematological disorder registry and we asked the physicians to participate in this study (Fig. 3). The potential size of patient cohort is 181, including 116 idiopathic and 65 secondary PRCA and these patients will be followed up during the next ten years. The PRCA2016 cohort study is expected to reveal the unbiased results regarding the long-term survival and quality of life in PRCA following immunosuppression.

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