Human Epidermal Growth Factor Receptor 2 (HER2) PET Imaging of HER2-Low Breast Cancer with [68Ga]Ga-ABY-025: Results from a Pilot Study

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FIGURE 1.
Flowchart of accrual and study-related investigations in pilot study of HER2 PET with [⁶⁸Ga]Ga-ABY-025 for patients with HER2-low mBC.
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FIGURE 2.
Maximum-intensity-projection values from all 10 patients included in pilot study of HER2 PET with [⁶⁸Ga]Ga-ABY-025. Pat = patient.
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FIGURE 3.
Correlation between HER2 IHC in biopsies of metastatic lesions and SUV_max on HER2 PET.
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FIGURE 4.
Representative images from patient with SUV_max of 24.9 and HER2 IHC score of 0 in biopsy specimen. Metastatic lesion in segment 3 of liver shows inhomogeneous intravenous contrast uptake due to central necrosis (arrows). Inhomogeneous nature of metastatic lesion was verified under ultrasound before biopsy. Liver biopsy (bottom right) shows status for HER2 IHC score of 0.
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FIGURE 5.
Disease heterogeneity noted on HER2 PET. Per patient, biopsied lesion, median SUV_max, and range of all tumor lesions measured on HER2 PET are indicated by thick black line. HER2 IHC result is also shown.

TABLE 1.

Characteristics of Patients Included in Pilot Study, Previous Treatment, and Tumor Biology Features

					Previous metastatic biopsies
Patient	Year of birth	Year of mBC diagnosis	Previous palliative systemic therapies in metastatic setting	Breast cancer type	Previous biopsy site	ER/PR/Ki-67	HER2 IHC	HER2 ISH
1	1945	2015	Letrozol, eribulin, paclitaxel, fulvestrant, exemestane + palbociclib, vinorelbin	Ductal	Liver	100/100/10	2	1.54
					Liver	100/95/17	2	2.4
					Liver	100/0/16	2	2.7
2	1962	2022	Newly diagnosed mBC	Ductal	Primary tumor	100/90/38	1
3	1957	2016	Anastrozole, fulvestrant + palbociclib, capecitabine	Ductal	Liver	100/0/25	2	1.0
4	1966	2018	Letrozole/palbociclib, PEGylated doxorubicin, tamoxifen, capecitabin	Ductal	Liver	50/0/43	1+
5	1972	2020	Anastrozole/goserelin/palbociclib, fulvestrant/ribociclib	Lobular	Primary tumor (intracranial disease)	100/70/20	2
6	1974	2019	Capecitabin, eribulin, carboplatin/paclitaxel, sacituzumab govitecan	Lobular	Breast/skin	0/0/10	1+
7	1973	2018	Fulvestrant/ribociclib	Ductal	Breast (relapse)	80/0/32	2+	2,3
8	1949	2020	Letrozole, fulvestrant/ribociclib	Ductal	Bone	100/0/30	0
9	1963	2014	Paclitaxel, letrozole, fulvestrant/ribociclib, capecitabin	Ductal	Liver	90/5/1
					Bone	100/50/10
10	1966	2020	Eribulin, capecitabin	Lobular	Bone	0/0/15		2–4/2–4/1.0

TABLE 2.

Study-Related Findings from HER2 PET and Paired Tumor Biopsy in 10 Patients in HER2-Low Pilot Study

		HER2 PET/CT results
			SUV for spleen		SUV for liver^*		SUV for left myocardium			Study-specific biopsies
Patient	Lesion site(s)	SUV_max for tumor	Max	Mean	Max	Mean	Max	Mean	TBR	Site	ER/PR/Ki-67	HER2 IHC biopsy	HER2/C17 gene amplification quote
1	Liver	12.9	2.6	1.9	9.1	7.8	3.1	2.2	6.8	Liver	100/100/19	1+	2.85/1.0/2.85
2	Bone, lymph nodes	6.1	3.9	2.6	13.7	7.0	4.4	3.0	2.3	Lymph node	0/0/95	1+
3	Liver	28.7	3.0	1.8	NA	NA	4.1	2.6	15.9	Liver	80/70/NA	2+	3.3/2.3/1.4
4	Bone, liver	10.7	5.0	3.3	NA	NA	3.2	2.2	3.2	Liver	80/70/78	1+	4.4/2.5/1.76
5	Bone, liver	24.9	3.9	2.6	13.4	10.2	4.1	2.9	9.6	Liver	30/0/60	0
6	Bone, skin, liver	3.7	2.8	2.2	NA	NA	3.1	2.1	1.7	Skin	0/0/39	0
7	Breast, brain	10.3	2.3	1.7	13.8	11.0	3.8	2.9	6.1	Breast	60/0/40	2+	3.6/1.45/2.48
8	Liver	33.4	2.7	2.1	13.3	9.7	4.1	3.0	15.9	Liver	95/0/3	2+	1.3/1.8/0.7
9	Bone, liver	19.0	3.0	2.3	NA	NA	3.7	3.0	8.3	Liver	95/95/13	2+	2.25/1.55/1.45
10	Liver, bone	12.0	2.7	1.6	NA	NA	2.7	1.8	7.5	Liver	0/0/33	2+	2.65/1.35/1.96