Transient/reversible ring sideroblasts in bone marrow of patients post cytotoxic therapies for primary malignancies

The diagnosis of therapy-related myelodysplastic syndrome (t-MDS) in the absence of increased myeloblasts or cytogenetic abnormalities is challenging. The presence of ring sideroblasts (RS) in this setting is often used to support the diagnosis of t-MDS. In this study, we reviewed 843 patients initially classified as therapy-related myeloid neoplasm in our hospital over 10 years. Nineteen (2.3%) patients had a normal karyotype, <5% bone marrow (BM) blasts, and ≥15% RS (17-70%), forming this study group. After reviewing clinical charts and follow-up BM specimens, we confirmed the diagnosis of MDS in 13 patients, but in 6 patients the blood counts returned to normal and RS and associated dyserythropoiesis disappeared in the follow-up BM biopsy. With a median follow-up of 21 months, none of these 6 patients died of BM causes. Compared with t-MDS cases, the 6 patients with transient/reversible RS showed comparable numbers of RS and BM blasts, but infrequent dysplasia involving non-erythroid lineages. We conclude that the presence of ≥15% RS in the post-therapy setting is not necessarily indicative of a clonal stem cell neoplasm. Four patients with transient/reversible RS received α-interferon therapy which may contribute to RS formation in this setting.