First, we found that in zebrafish larvae neutrophils express high levels of cxcr4b, the homolog of human CXCR4 and paralog of zebrafish cxcr4a. Then, we used a cxcr4b homozygote mutant zebrafish (also known as odysseus or ody) and showed that engrafted human tumor cells failed to form micrometastases in the CHT region. The gene discussed is CXCR4; the disease is neoplasm.