Poster

As melanoma metastasizes early into regional lymph nodes, the excision of the first draining lymph node (SLNE) is a staging procedure to detect possible lymph node metastasis in patients with melanoma and to eventually prolong distant disease-free survival. Nevertheless, the present gold standard for assessing the SLN by means of lymphoscintigraphy with 99m-Technetium suffers from poor specificity that leads to high rates of false negative results (up to 38 %) for lymph node metastasis. If a non-invasive approach reliably and specifically detects melanoma metastasis in the SLN, the selection of patients receiving SLNE will be more accurate. To imitate possible heterogeneous discrepancies in human melanoma antigens and enhance the transferability of our model, we subcutaneously transplant the human melanoma cells M24met and MV3 that reliably induce lymph node metastasis in NOD SCID mice. Melanoma metastasis shall non-invasively be detected in vivo with the help of fluorescent antibodies bound to the cell-surface antigen melanoma-associated chondroitin sulfate proteoglycan (MCSP) by using Multispectral Optoacoustic Tomography (MSOT). MSOT is a hybrid imaging technique, combining high-resolution ultrasound with molecular specific optical excitation. The feasibility of detecting a fluorescent antibody specifically attached to tumor cell metastasis by means of MSOT could already be demonstrated for orthotopic xenograft tumor tissue in vivo. Additionally, we could already non-invasively determine the metastatic status of sentinel lymph nodes in melanoma by means of indocyanine green. Still, the detection of metastasis with the help of indocyanine green and MSOT lacks sufficient specificity. We have already established a fluorescent antibody that specifically attaches to the human melanoma cell lines and can be detected by MSOT in vitro. After in-vivo visualization of possible lymph node metastasis, mice will be sacrificed and carefully autopsied. The occurrence of antibody attachment to MCSP will be evaluated and possible melanoma metastasis histopathologically assured. These results will be correlated with the in-vivo results provided by MSOT. Our main ambition is to significantly improve the specificity of a novel multispectral optoacoustic tomography (MSOT) assessment protocol for detecting melanoma cell spread to the first draining lymph node (SLN) in vivo.