Incidental Detection of Ischemic Myocardium on ⁶⁸ Ga-FAPI PET/CT

Abstract

Recent studies using Ga-68-labeled fibroblast activation protein inhibitors (FAPI) PET have shown strong association between focal uptake of FAPI in myocardium and presence of coronary artery disease. We present an interesting case of a 76-year-old female with breast cancer with incidental uptake on FAPI PET in apex and septal wall of left ventricle myocardium correlating with findings of ischemia on dobutamine stress myocardial perfusion imaging and anatomical stenosis on coronary angiography.

A 76-year-old female with locally advanced breast cancer (estrogen receptor–positive and progesterone receptor/human epidermal growth factor receptor-2 negative) underwent whole body 2-deoxy-2-(fluorine-18)fluoro-d-glucose (¹⁸F-FDG) (Fig. 1) and Gallium-68-labeled FAP-specific inhibitor (⁶⁸ Ga-FAPI) positron emission tomography/computed tomography (PET/CT) prior to treatment initiation (Fig. 2). On FDG PET/CT, both primary left breast lesion (SUVmax—4.47, Fig. 1a) and axillary nodes (SUVmax—2.89, Fig. 1b) showed a lower standardized uptake and lower tumor-to-background uptake compared to FAPI PET (SUVmax—11.8 and 9.21, respectively; Fig. 2a, b). Incidentally noted, a 3-cm nodule in the isthmus of thyroid showed intense FDG uptake (SUVmax—14, Fig. 1c) but no significant FAPI uptake (Fig. 2c). Fine needle aspiration cytology from this nodule was negative for malignancy. Incidentally, focal uptake was also noted in the apex, apico-infero-lateral, and apico-antero-septal segments of the left ventricle on both FDG and FAPI PET (Fig. 3a, b, bold white and yellow arrows, respectively). A dobutamine stress myocardial perfusion single-photon emission tomography imaging (SPECT MPI) with ^99mTc-Sestamibi was done after 2 days of PET/CT for pre-operative cardiac risk stratification which showed moderate stress-induced ischemia in the apex, apico-infero-lateral, and apico-antero-septal segments (Fig. 4, short axis, horizontal long axis, and vertical long axis views, white arrow heads in stress images). Coronary angiography performed a day later confirmed a critical stenosis in the mid-left anterior descending artery branch (Fig. 5, right anterior oblique cranial view, blue arrow showing cutoff of mid-LAD).

Fig. 1.

FDG PET/CT showing low grade FDG avid left breast lesion a SUVmax 4.47), axillary nodes b SUVmax 2.89) and intense FDG uptake in enhancing lesion in isthmus of thyroid c SUVmax 14)

Fig. 2.

Ga-68 FAPI PET/CT showing intense and higher than FDG uptake in the left breast lesion a SUVmax 11.8), axillary nodes b SUVmax 9.21) and no signficant uptake in enhancing lesion in isthmus of thyroid c

Fig. 3.

Focal intense uptake noted in apex, apico-infero-lateral, and apico-antero-septal segments of the left ventricle on both FDG and FAPI PET

Fig. 4.

Moderate stress-induced ischemia in the apex, apico-infero-lateral, and apico-antero-septal segments

Fig. 5.

Coronary angiography performed a day later confirmed a critical stenosis in the mid-left anterior descending artery branch

Expression of fibroblast activation protein (FAP) in myocardial ischemia/infarction and its relevance in cardiac remodeling has previously been demonstrated in small animal models [1, 2]. Recently, clinical validation studies have shown a significant correlation of myocardial uptake of radiolabeled FAP-specific inhibitor (FAPI) with presence of cardiovascular risk factors, presence of coronary artery disease, and left ventricular ejection fraction [3, 4]. The image presented here is a proof of this concept where focal uptake of FAPI was in concordance with dobutamine stress SPECT MPI and FDG PET/CT findings suggestive of sub-clinical significant myocardial ischemia which was confirmed on coronary angiography. Utility of ⁶⁸ Ga-FAPI PET/CT for non-invasive cardiac risk stratification should be explored further in larger prospective studies with multi-modality imaging correlation.

Author Contribution

All authors have contributed equally for the case study.

Availability of Data and Material

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

Compliance with Ethical Standards

Competing Interests

Piyush Chandra, Satish Nath, Jaishankar Krishnamoorthy, and Guru Prasad Sogunuru declare no competing interests.

Ethics Approval and Consent to Participate

Case study was approved by the MIOT International Ethics committee with prior informed consent obtained by the patient.

Consent for Publication

Informed consent was obtained from the patients with regard to publication.