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The goal of this study was to characterize the relationship between tumor uptake of 64Cu-DOTA-trastuzumab as measured by PET/CT and standard, immunohistochemistry (IHC)-based, histopathologic classification of human epidermal growth factor receptor 2 (HER2) status in women with metastatic breast cancer (MBC). Methods: Women with biopsy-confirmed MBC and not given trastuzumab for 2 mo or more underwent complete staging, including 18F-FDG PET/CT. Patients were classified as HER2-positive (HER2+) or -negative (HER2-) based on fluorescence in situ hybridization (FISH)-supplemented immunohistochemistry of biopsied tumor tissue. Eighteen patients underwent 64Cu-DOTA-trastuzumab injection, preceded in 16 cases by trastuzumab infusion (45 mg). PET/CT was performed 21-25 (day 1) and 47-49 (day 2) h after 64Cu-DOTA-trastuzumab injection. Radiolabel uptake in prominent lesions was measured as SUVmax Average intrapatient SUVmax (max>pt) was compared between HER2+ and HER2- patients. Results: Eleven women were HER2+ (8 immunohistochemistry 3+; 3 immunohistochemistry 2+/FISH amplified), whereas 7 were HER2- (3 immunohistochemistry 2+/FISH nonamplified; 4 immunohistochemistry 1+). Median max>pt for day 1 and day 2 was 6.6 and 6.8 g/mL for HER 2+ and 3.7 and 4.3 g/mL for HER2- patients (P < 0.005 either day). The distributions of max>pt overlapped between the 2 groups, and interpatient variability was greater for HER2+ than HER2- disease (P < 0.005 and 0.001, respectively, on days 1 and 2). Conclusion: By 1 d after injection, uptake of 64Cu-DOTA-trastuzumab in MBC is strongly associated with patient HER2 status and is indicative of binding to HER2. The variability within and among HER2+ patients, as well as the overlap between the HER2+ and HER2- groups, suggests a role for 64Cu-DOTA-trastuzumab PET/CT in optimizing treatments that include trastuzumab.

Background: The potent immune effects of interleukin‐2 (IL‐2) for cancer therapy can be increased by genetic fusion of IL‐2 to the Fc domain of an antibody (IL‐2‐Fc) or tumor targeted by genetic fusion to a whole antibody known as an immunocytokine (ICK). Methods: An anti‐CEA ICK (M5A‐IL‐2) was compared to an IL‐2‐Fc fusion protein using tumor therapy and PET imaging in CEA transgenic immunocompetent mice bearing CEA positive colon or breast tumors. Combination with stereotactic radiation therapy (SRT) was performed with either ICK or IL‐2‐Fc. Results: ICK and IL‐2‐Fc had comparable antitumor effects in both tumor models, although ICK had higher tumor uptake and slower blood clearance than an IL‐2‐Fc. Analysis of IFNγ+/CD8+ and FoxP3+/CD4+ T cells revealed higher levels of IFNγ‐producing CD8+ T cells in ICK treated mice versus more efficient Treg elimination in IL‐2‐Fc treated mice. No significant or lasting toxicity was detected for either agent. Combination therapies with SRT revealed comparable efficacy and induction of immune memory for both ICK and IL‐2‐Fc when mice were rechallenged post‐therapy. Conclusions: IL‐2‐Fc had comparable antitumor efficacy to CEA‐targeted M5A‐IL‐2 ICK, while both fusion proteins induced immune memory when combined with SRT. Differences in the therapeutic mechanisms of both agents were observed. [ABSTRACT FROM AUTHOR]