A patient with anemia is found to have ringed sideroblasts in their bone marrow biopsy. What is the most likely diagnosis?

Ringed sideroblasts are erythroblasts with abnormal mitochondrial accumulations of iron, visible as rings around the nucleus. This finding is characteristic of myelodysplastic syndromes, particularly refractory anemia with ringed sideroblasts (RARS), a subtype of myelodysplastic syndrome.