Final answer:
Phase I clinical trials involve patients with various types of tumors to assess safety and pharmacokinetics, while Phase II clinical trials focus on a single tumor type to evaluate efficacy and dosing.
Step-by-step explanation:
In clinical trials, Phase I studies typically involve patients who may have various types of tumors, as the main goal is to investigate safety, tolerance, and pharmacokinetic properties of the compound. Phase II studies, in contrast, are more selective, focusing on a single tumor type to evaluate the efficacy and optimal dosing of the drug. This transition from a broad spectrum in Phase I to a more targeted approach in Phase II is critical to establishing the compound's effectiveness against a specific type of cancer, providing the necessary evidence to move forward to Phase III clinical trials.
Phase I trials also serve to define the safe dosing range, and Phase II trials expand upon these findings by assessing dose/exposure response and conducting dose ranging studies for effective doses. Successful candidates from these trials then advance to Phase III, which can include several thousand patients in a large, diverse database to assess the efficacy and safety profile of the drug comprehensively.