CD8 PET imaging shows modest correlation with biopsy CD8 counts in solid tumor patients on immunotherapy
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Key Takeaway
Interpret CD8 PET imaging correlation with biopsy CD8 counts as preliminary and modest in solid tumors.
This Phase II prospective multicenter study evaluated the correlation between CD8 PET imaging using [Zr]Zr-berdoxam-crefmirlimab and intratumoral CD8 cell counts assessed by immunohistochemistry (IHC) of core needle biopsies. The study included 49 patients with solid tumors receiving immune checkpoint blockade therapy, with 70 biopsies analyzed (37 baseline and 33 on-treatment). The primary outcome was the correlation between CD8 PET imaging parameters and IHC CD8 cell quantity.
The main finding was a modest positive correlation between the standard uptake value mean of the biopsied tumor normalized to aorta and IHC CD8 counts, with a correlation coefficient of 0.49 (95% CI 0.26 to 0.59). In a subgroup of patients with renal cell carcinoma, the correlation was stronger at 0.71 (95% CI 0.48 to 0.85), though the absolute number of biopsies in this subgroup was not reported. The study reported that repeat CD8 PET imaging on-treatment was safe, though specific adverse event data were not provided.
Key limitations include that core needle biopsies do not fully represent the intratumoral heterogeneity of CD8 cell distribution, which likely contributed to the modest overall correlation. The study provides no data on correlation with immunotherapy clinical outcomes. As a Phase II study, these findings represent preliminary evidence of association only; correlation does not imply causation. Further validation in larger studies is needed to determine whether CD8 PET imaging can reliably predict treatment response or guide clinical decisions.
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View Original Abstract ↓
BACKGROUND: CD8 T cells mediate the effects of cancer immunotherapies. CD8 positron emission tomography (PET) imaging with [Zr]Zr-berdoxam-crefmirlimab enables whole body CD8 cell assessment and has been shown to be safe in Phase I evaluation. The correlation between CD8 PET imaging parameters and the quantity of CD8 cells assessed by the gold standard of immunohistochemistry (IHC) is unknown.
METHODS: The Phase II, prospective multicenter study (iCorrelate) tested the correlation between CD8 PET and CD8 cells by IHC of core needle biopsies from patients with solid tumors receiving immune checkpoint blockade. The safety of repeat CD8 PET was additionally analyzed.
RESULTS: 49 patients had 70 biopsies (37 baseline and 33 on-treatment) for correlating CD8 PET with IHC. Standard uptake value mean of the biopsied tumor normalized to aorta showed a correlation with IHC of 0.49 (95% CI 0.26 to 0.59). The correlation was 0.71 (95% CI 0.48 to 0.85) in patients with renal cell carcinoma. Repeat CD8 PET imaging on-treatment was safe.
CONCLUSIONS: We found a modest correlation between CD8 PET with [Zr]Zr-berdoxam-crefmirlimab and intratumoral CD8 cell counts, likely because core needle biopsies do not fully represent the intratumoral heterogeneity of the CD8 cell distribution. Continued research is essential to evaluate in vivo CD8 PET signals, autoradiography, and CD8 T-cell presence by IHC in fully resected tumors. Further studies investigating the correlation between CD8 PET and immunotherapy outcomes are necessary to determine whether CD8 PET imaging could become a valuable tool for guiding immunotherapy development and informing clinical decision-making.
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