Nano-sized dendrimer MR contrast tracks lymphatic drainage of breast cancer

CONTEXT: Sentinel lymph node biopsy offers the potential for a less invasive means of assessing nodal involvement in breast cancer, compared with conventional axillary lymph node dissection.

A way to identify sentinel nodes that is more precise than gadolinium-enhanced MR is needed, however. At the International Society for Magnetic Resonance in Medicine conference in Kyoto, Japan, investigators from the National Cancer Institute reported encouraging results in a mouse experiment using a nano-sized dendrimer contrast agent to image lymphatic drainage in breast cancer.

RESULTS: The nano-sized polyamidoamine G6 dendrimer contrast agent (G6) was compared with conventional gadolinium-DTPA contrast material for evaluating lymph nodes and lymphatic drainage in normal mice and transgenic mice that develop spontaneous breast cancers. In the tumor-bearing mice, lymphatic flow from breast tumors to metastatic lymph nodes was readily visualized by means of dynamic micro-MR mammolymphangiography (dmMRML) using the nano-sized G6 contrast agent. On MR assessment, nodes containing solid tumor demonstrated filling defects or rim enhancement, allowing detection and diagnosis of micrometastasis. In normal mice, dmMRML visualized the axillary lymph node and its draining lymphatics at the initial time point. Two other lymph nodes (lateral thoracic and superficial cervical) and their draining lymphatics were also visualized. Lymphatic drainage was not seen when the researchers used gadolinium contrast, according to NCI staff scientist Dr. Histaka Kobayashi!.

IMAGES: Draining lymphatic vessels and lymph nodes from left breast tissue in a normal mouse are clearly depicted in Figure 1 on a dynamic 3D image acquired 30 minutes after G6 nano-sized contrast injection. Figure 2 shows a schema of that morphology. In Figure 3, fused surface and volume-rendered images of 3D dmMRML of a normal mouse show both the skin and the draining lymphatic system of the left breast.

IMPLICATIONS: Superior temporal and spatial resolution of the dmMRML technique should have applicability to the study of lymph nodes and lymphatic vessels in a variety of tumor types. The next step in the evaluation of the technique will likely focus on melanoma, Kobayashi said.