Use of 68Ga-FAPI PET/CT for Detecting Myeloid Sarcoma of the Breast and Assessing Early Response to Chemotherapy.

Myeloid sarcoma is a rare presentation of acute myeloid leukemia as a solid tumor at various extramedullary sites. In this case, we report 18F-FDG and 68Ga-FAPI PET/CT findings in an 18-year-old woman with biopsy-proven myeloid sarcoma involving the left breast. 68Ga-FAPI PET/CT showed a far better tumor-to-background contrast than 18F-FDG PET/CT in the left breast mass. Moreover, follow-up 68Ga-FAPI PET/CT after 2 cycles of chemotherapy revealed a reduction in tumor size with decreasing activity in the myeloid sarcoma lesions.