Zirconium-89-Trastuzumab Positron Emission Tomography As a Tool to Solve a Clinical Dilemma in a Patient With Breast Cancer

Case ReportA 34-year-old woman was diagnosed with two right-sided primary breast cancers.One tumor was 10 cm in diameter, histologic grade 3, and negative for estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2), whereas the other tumor was 6.5 cm in diameter, grade 3, and ER positive, PgR negative, and HER2 positive.Standard workup revealed no metastases.The primary treatment of the patient consisted of a right-sided mastectomy with axillary lymph node dissection.This dissection showed tumor involvement in 11 of 14 lymph nodes.Adjuvant treatment consisted of doxorubicin and cyclophosphamide followed by trastuzumab combined with paclitaxel.Thereafter, trastuzumab monotherapy was continued for 1 year.Chemotherapy was followed by treatment with tamoxifen and leuprorelin.Two years after the diagnosis, during a routine checkup, the serum cancer antigen 15.3 level was increased to 70 kU/L.Physical examination of the patient was unremarkable.On computed tomography (CT) scan, dissemination analysis showed a large mediastinal mass and a small liver lesion, although no lesions were present on the bone scan.To determine which primary tumor had metastasized, a biopsy of the liver lesion was performed, which showed no tumor cells on histologic examination.To obtain tissue of the mediastinal lesion, a mediastinoscopy was required.Therefore, the patient was referred to our hospital to assess the HER2 status of the tumor noninvasively by means of zirconium-89-trastuzumab ( 89 Zr-trastuzumab) positron emitting tomography (PET) imaging.The procedure was carried out as described earlier, with acquisition of the PET images 4 days after intravenous administration of 37 MBq 89 Zr-trastuzumab (protein dose 50 mg). 1 The PET scan showed uptake in the mediastinal mass, lymph nodes in the neck region level 4 on both sides and level 3 on the right side, and sacral spine (Fig 1).No liver lesions were detected.It was concluded from the 89 Zr-trastuzumab PET scan that the metastatic process was HER2 positive.Given the progression during hormonal treatment and the large mediastinal mass, tamoxifen treatment was temporarily discontinued, and chemotherapy was initiated.The patient received three cycles of fluorouracil, epirubicin, and cyclophosphamide followed by three cycles of paclitaxel and trastuzumab.Thereafter, the CT scan showed a partial tumor response, and trastuzumab was continued in combination with the aromatase inhibitor anastrozole.