99mTc-HYNIC-FAPI-46 SPECT/CT Uptake in Lactating Breasts.

A 36-year-old woman with a history of medullary thyroid carcinoma was referred for 99mTc-HYNIC-FAPI-46 scan. Her calcitonin levels gradually increased after external beam radiation therapy, whereas her CEA levels were stable. A few suspicious tumoral lymphadenopathies were localized to the superior mediastinum. Interestingly, bilateral physiologic breast uptake was noticed, which was presumed to be due to lactation in the past 18 months. To our knowledge, physiologic breast uptake in 99mTc-HYNIC-FAPI imaging has not been previously reported.