《The Emperor of All Maladies: A

Choriocarcinoma cells secrete a marker, a hormone called choriogonadotropin, a protein that can be measured with an extremely sensitive test in the blood (a variant of this test is used to detect pregnancies). Early in his experiments, Li had decided that he would use that hormone level to track the course of the cancer as it responded to methotrexate. The hcg level, as it was called, would be a surrogate for the cancer, its fingerprint in the blood.

Li had stumbled on a deep and fundamental principle of oncology: cancer needed to be systemically treated long after every visible sign of it had vanished. The hcg level--the hormone secreted by choriocarcinoma--had turned out to be its real fingerprint, its marker.

• choriocarcinoma /ˌkɔrioˌkɑrsəˈnomə/ n. 绒毛膜癌
• choriogonadotropin n. 绒毛膜促性腺激素
• secrete /sɪˈkriːt/ v. (of part of the body or a plant 身体或植物器官) to produce a liquid substance 分泌
• hormone /ˈhɔːrmoʊn/ n. 激素；荷尔蒙
• protein /ˈproʊtiːn/ n. 蛋白质
• methotrexate /ˌmɛθə'trɛkset/ n. 甲氨蝶呤,氨甲蝶呤,氨甲叶酸(一种抗肿瘤药)
• surrogate /ˈsɜːrəɡət/ adj. 替代的；代用的
• stumble /ˈstʌmbl/ v. to hit your foot against sth while you are walking or running and almost fall 绊脚
  stumble across/on/upon sth/sb 意外发现；偶然遇见
• oncology /ɑːnˈkɑːlədʒi/ n. 肿瘤学
• vanish /ˈvænɪʃ/ v. （莫名其妙地）突然消失；不复存在；消亡；绝迹

绒毛膜癌细胞分泌一种称之为绒毛膜促性腺激素的标记物，这种蛋白质能在血液中被极其精确地测量出来（和这种测试类似的另外一种测试被用来验孕）。在他早期的实验中，李敏求决定要用这种激素水平来追踪癌症对甲氨蝶呤的反应过程。正如它的名字一样，hcg水平将成为癌症的代言人，成为癌症在血液中的指纹。

李敏求意外地发现了一个深刻而基础肿瘤学原理：癌症必须在其每一种可见迹象都消失后，继续保持系统性的治疗。hcg水平——绒毛膜癌分泌的激素，才是它真正的指纹、真正的标记。