Figure 1.

Cancer cells can acquire drug resistance via genetic and non-genetic adaptation mechanisms. Cancer cells initially respond to drug exposure. However, few malignant cells can survive the treatment. (A) Pre-existing clones, with specific genetic mutations, are intrinsically resistant to targeted therapy and allow for the tumor to regrow. (B) In the absence of pre-existing genetic mutations, few drug-tolerant persister cells are spared during drug treatment, and over time, these cells can give rise to tumor relapse. (C) From the pool of drug-tolerant persister cells, different genetic and non-genetic resistance mechanisms can emerge and contribute to tumor regrowth.