The potential for personalized cancer management has long intrigued experienced researchers as well as the naive student intern. Personalized cancer treatments based on a tumor's genetic profile are now feasible and can reveal both the cells' susceptibility and resistance to chemotherapeutic agents. In a weeklong laboratory investigation that mirrors current cancer research, undergraduate and advanced high school students determine the efficacy of common pharmacological agents through in vitro testing. Using mouse mammary tumor cell cultures treated with "unknown" drugs historically recommended for breast cancer treatment, students are introduced to common molecular biology techniques from in vitro cell culture to fluorescence microscopy. Student understanding is assessed through laboratory reports and the successful identification of the unknown drug. The sequence of doing the experiment, applying logic, and constructing a hypothesis gives the students time to discover the rationale behind the cellular drug resistance assay. The breast cancer experiment has been field tested during the past 5 yr with more than 200 precollege/undergraduate interns through the Gains in the Education of Mathematics and Science program hosted by the Walter Reed Army Institute of Research. (Contains 6 figures and 5 tables.)