99m Tc-HYNIC-FAPI-46 SPECT/CT Uptake in Lactating Breasts

Area of Science:

• Nuclear Medicine
• Oncologic Imaging
• Radiopharmaceutical Development

Background:

• Medullary thyroid carcinoma (MTC) management requires sensitive imaging for recurrence detection.
• Fibroblast activation protein (FAP) targeted imaging is emerging for various cancers.
• 99mTc-HYNIC-FAPI-46 is a novel radiotracer for FAP imaging.

Observation:

• A 36-year-old woman with MTC underwent 99m Tc-HYNIC-FAPI-46 scan due to rising calcitonin levels post-radiation.
• Suspicious lymphadenopathy in the superior mediastinum was identified.
• Unexpected bilateral physiologic breast uptake was observed.

Findings:

• The breast uptake was presumed to be related to lactation within the past 18 months.
• This represents the first reported instance of physiologic breast uptake in 99m Tc-HYNIC-FAPI imaging.
• Tumoral lymphadenopathies were successfully localized, aiding in MTC surveillance.

Implications:

• Physiologic uptake patterns in 99m Tc-HYNIC-FAPI imaging need further characterization.
• Understanding benign uptake can improve the accuracy of FAP-targeted cancer detection.
• This finding highlights the importance of considering patient-specific factors in interpreting novel imaging results.