Essentials of Genetics 9th Edition by Michael Palladino William Klug, Michael Cummings, Charlotte Spencer

Exercise 3

I thought it was safe
A middle-aged woman taking the breast cancer drug tamoxifen for ten years became concerned when she saw a news report with disturbing information. In some women, the drug made their cancer more aggressive and more likely to spread. Other women with breast cancer, the report stated, do not respond to tamoxifen at all, and 30 to 40 percent of women who take the drug eventually become resistant to chemotherapy. The woman contacted her oncologist to ask some questions:
Why does it seem that some drugs are thought to be safe one day and declared unsafe the next day?