Page 60 - 89Zr-Immuno-PET:Towards a Clinical Tool to Guide Antibody-based Therapy in Cancer

Chapter 3
Figure 4. Fusion (C) of CT (A) and coronal immuno-PET (B) images of head and neck cancer patient 16 (same as in Figure 2), with a tumor in the left tonsil and lymph node metastases at the left (level II and III) and right (level II) side of the neck. Images were obtained 72 h postinjection. In these slices, only lymph node metastases are visible.
Following this feasibility study, the exact position of immuno-PET using 89Zr- cMAb U36 within the current armamentarium for diagnosis of head and neck cancer still has to be established. One has to realize that apart from noninvasive imaging methods for the neck, invasive diagnostic procedures are also available, e.g., ultrasound-guided fine-needle aspiration cytology. In ultrasound-guided fine-needle aspiration cytology, selection of lymph nodes to be aspired is based on known patterns of lymphatic spread and/or lymph node size and morphology as assessed with ultrasound, sometimes after obtaining evidence by CT or MRI scan. Although ultrasound-guided fine-needle aspiration cytology enables detection of lymph node metastases at a single cell level it has also some unfavorable aspects, however: (a) its accuracy is strongly dependent on the skills of the ultrasonographer and the cytopathologist, (b) it is an invasive method, and (c) it gives only information of a selected part of the neck and not on the primary tumor or distant metastases.
At the current stage of development, immuno-PET with 89Zr-cMAb U36 is not able to detect micrometastases in the neck, an observation that has also been previously reported for FDG-PET (17,18). False-negative observations in the present study were mostly due to the presence of small metastatic lymph nodes with minimal tumor involvement (Table 5), whether or not such small tumors are efficiently targeted by MAb U36, as previously shown in a biodistribution study with mMAb U36 (19).
From a diagnostic point of view, immuno-PET with 89Zr-cMAb U36 might also have perspectives for the detection of distant metastases. Approximately 25% of advanced-stage (stage III and IV) head and neck cancer patients develop distant
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