Negative 18 F-FES PET/CT Despite Estrogen Receptor Positivity by Immunohistochemistry

Area of Science:

• Oncology
• Nuclear Medicine
• Pathology

Background:

• Immunohistochemistry (IHC) is standard for assessing estrogen receptor (ER) status in breast cancer.
• 18F-fluoro-estradiol (18F-FES) PET/CT is used for select ER+ metastatic breast cancer patients, predicting response to endocrine therapy (ET).
• Tracer avidity on 18F-FES PET/CT typically correlates with favorable responses to ET.

Purpose of the Study:

• To investigate cases of metastatic breast cancer that are ER+ by IHC but show no tracer avidity on 18F-FES PET/CT.
• To hypothesize the reason for lack of tracer avidity despite positive IHC.
• To determine the implications for endocrine therapy response.

Main Methods:

• Review of 2 cases of metastatic breast cancer.
• Comparison of Immunohistochemistry (IHC) results with 18F-FES PET/CT imaging.
• Correlation of imaging findings with predicted response to endocrine therapy.

Main Results:

• Two patients with ER+ breast cancer by IHC showed a lack of 18F-FES uptake on PET/CT.
• This suggests that ER detected by IHC may be nonfunctional and unable to bind estrogen.
• Nonfunctional ER may indicate resistance to endocrine therapy.

Conclusions:

• 18F-FES PET/CT may identify patients with ER+ breast cancer whose receptors are nonfunctional.
• Patients with non-avid ER on 18F-FES PET/CT may not benefit from endocrine therapy.
• This highlights the importance of functional ER assessment for guiding breast cancer treatment.