Heterotopic transplantation mouse model for lymph node metastasis. a. A subcutaneously growing tumor was excised and a small piece was transplanted into the elbow of another nude mouse. b. Gross appearance of excised accessory lymph nodes. c. Hematoxylin and Eosin staining of the excised lymph node (yellow arrow indicates metastatic cancer cells). d. Estimated number of cells in the accessory axillary lymph nodes, as measured by quantitative real-time RT-PCR with the human Alu sequence.