Another problem: While the gene can be directly injected into tumors that doctors can see, more clever delivery methods are needed to get it into metastasized cancer cells.

• 另一个问题是，虽然基因能被直接注射到医生所能看到的肿瘤里，但是如果癌细胞发生转移，还需要更好的方法把基因输送过去。