One of the primary challenges in assessing the efficacy of new cancer drugs is the heterogeneity of the disease. Cancer is not a single disease but a collection of related diseases, each with its own genetic and molecular profile. This makes it difficult to predict how a new drug will perform across different types of cancer and patient populations. Additionally, the side effects and toxicity profiles of new drugs can complicate efficacy assessments, as a treatment must be both effective and tolerable.
