Schabel等假设,药物杀死肿瘤细胞的能力,不仅取决于药物的剂量,而且也取决于肿瘤细胞的数量。用放疗、手术或两者联合治疗消灭瘤体后,再用对转移灶有效的药物,根除残留的肿瘤,这种治疗是有希望的。尽管一些病人最初化疗有效,但往往是短暂的。这意味着移行细胞癌常产生细胞抗药性。已证明,肿瘤产生抗药性的机制是减少药物的转运,增加其分解代谢或减低药物活性。化学预防预防癌症,特别是预防癌前期的新的药理学方法叫“化学预防”。化学预防就是在肿瘤形成的初期试用无细胞毒性的化学药物,阻止或逆转癌前细胞发展成浸润性肿瘤。 Schabel et al. hypothesized that the ability of drugs to kill tumor cells depends not only on the dose of the drug but also on the number of tumor cells. After radiotherapy, surgery, or a combination of the two to eliminate tumors, and then use drugs that are effective for metastasis, to eradicate residual tumors, this treatment is promising. Although some patients initially responded to chemotherapy, they were often short-lived. This means that transitional cell carcinoma often produces cell resistance. It has been demonstrated that the mechanism by which tumors develop drug resistance is to reduce the transport of drugs, increase their catabolism or reduce their activity. Chemoprophylaxis is a new pharmacological method for cancer prevention, especially prevention of precancerous conditions called “chemoprophylaxis.” Chemoprophylaxis is the trial of non-cytotoxic chemicals in the early stages of tumor formation, preventing or reversing precancerous cells from developing into invasive tumors.