BACKGROUND Granulocytic sarcoma (GS) is a rare malignant tumor, and relapse is even rarer in the breast and dorsal spine following allogeneic hematopoietic stem cell transplantation. Currently, a standard treatment regimen is not available. CASE SUMMARY A rare case of GS of the right breast and dorsal spine after complete remission of acute myelogenous leukemia is reported here. A 55-year-old female patient presented with a palpable, growing, painless lump as well as worsening dorsal compressive myelopathy. She had a history of acute myelomonocytic leukemia (AML M4) and achieved complete remission after chemotherapy following allogeneic hematopoietic stem cell transplantation. Imaging examinations showed the breast lump and C7-T1 epidural masses suspected of malignancy. Histologic results were compatible with GS in both the right breast and dorsal spine, which were considered extramedullary relapse of the AML treated 4 years earlier. CONCLUSION A rare case of GS relapse following allogeneic hematopoietic stem cell transplantation and guidelines for treatment are discussed.