The FDA typically requires Phase I, II, and III trials to be conducted to determine if the drug can be approved for use.

• A Phase I trial tests an experimental treatment on a small group of often healthy people (20 to 80) to judge its safety and side effects and to find the correct drug dosage.
• A Phase II trial uses more people (100 to 300). While the emphasis in Phase I is on safety, the emphasis in Phase II is on effectiveness. This phase aims to obtain preliminary data on whether the drug works in people who have a certain disease or condition. These trials also continue to study safety, including short-term side effects. This phase can last several years.
• A Phase III trial gathers more information about safety and effectiveness, studying different populations and different dosages, using the drug in combination with other drugs. The number of subjects usually ranges from several hundred to about 3,000 people. If the FDA agrees that the trial results are positive, it will approve the experimental drug or device.
• A Phase IV trial for drugs or devices takes place after the FDA approves their use. A device or drug's effectiveness and safety are monitored in large, diverse populations. Sometimes, the side effects of a drug may not become clear until more people have taken it over a longer period of time.

ref: https://www.nia.nih.gov/health/what-are-clinical-trials-and-studies

Single-arm trials

In this design, a sample of individuals with the targeted medical condition is given the experimental therapy and then followed over time to observe their response.

This design is employed when the objective of the trial is to obtain preliminary evidence of the efficacy of the treatment and to collect additional safety data, but is not generally used as confirmation of efficacy.

Single-arm studies are typically used in phase II of clinical trials, whose main objective is to determine whether a new treatment warrants further testing in a randomized phase III trial.

Placebo-controlled trials

Typically a group of subjects with the target disease is identified and randomized to two or more treatments (e.g., active treatment vs. placebo). A randomized participant only receives one treatment (or treatment strategy) during the duration of the trial. Participants are then followed over time and the responses are compared between groups.

Double-Blind Placebo-Controlled Clinical Trial

A double-blind, placebo-controlled clinical trial is a medical study involving human participants in which neither side knows who's getting what treatment and a placebo is given to a control group.

The highest-quality studies are also randomized, meaning that subjects are randomly assigned to placebo and intervention groups. The acronym DBRCT is commonly used for these types of studies.

Open-label trial

An open-label trial, or open trial, is a type of clinical trial in which both the researchers and participants know which treatment is being administered.

Single-blind trials

In a single-blind experiment, the individual subjects do not know whether they are so-called "test" subjects or members of an "experimental control" group.

Double-blind trials

In these double-blind experiments, neither the participants nor the researchers know which participants belong to the control group, nor the test group.

肿瘤药的临床试验，一般分为三个阶段：临床I期，临床II期，临床III期。

I期临床试验：一般招募的都是其他治疗已经失败的肿瘤病人，招募20-30个人，探索性地使用一款刚刚在动物上验证过安全性和有效性的崭新的药物。一种药物对老鼠兔子、猴子很安全、有一定疗效，那可不见得对人一定很安全，有没有效果更是未知数。所以，在国外，I期临床试验是经常出状况的，甚至每年都有不少病友为科学“英勇献身”。I期临床试验，主要目的，是看看一个全新的药品，用于人体是否安全，以及应该按照多大剂量，以何种频率给药最合适。所以，一般I期临床试验，都会设计很多种不同的剂量以及不同的给药间隔，比如：2mg 每天1次，5mg 每天1次，10mg 每天1次；2mg 每周1次，5mg 每周1次，10mg每周1次，20mg 每周1次，50mg 每周一次……总之，一切都是未知数。但是所有的全新的药品，必须经过这一关，能通过这一关的概率其实并不高。

II期临床试验：假如一个药品在I期临床试验中被证实，它的副作用的确是可控的，而且还对病友有效（哪怕只有极个别），那么药厂极可能会推动这个新药进入II期临床试验。II期临床试验，一般会招募四五十个，乃至上百个病人；有可能是随机对照的，也有可能并不是随机的。II期临床试验的目标，就是初步看一看这个药物的疗效如何。言外之言，参加II期临床试验的病友，大概率可以保证的是，这个药物的安全性应该还是不错的；但是有效性如何，并不能保证。

III期临床试验：假如一个药物在II期临床试验中，显示出了让医生和药厂的老板都激动的疗效。那么，有可能会被安排开始做III期临床试验。一个III期临床试验，大约需要招募几百人，甚至几千人，耗费十几亿乃至几十亿美金。因此，如果没有充分的把握，药厂可不会轻易开始一个III期临床试验。三期临床试验，绝大多数都是随机、双盲、对照试验。

● 所谓随机，就是病友参加到这个试验中，是被随机分配到实验组和对照组的，这里面就是概率问题，患者无法主动要求，医生和药厂也无法人为干预；抛一枚硬币，如果不作弊，你怎能在硬币落地停稳之前就知道到底是正面朝上还是反面朝上呢。

● 所谓双盲，就是不仅是病友不知道自己吃的是新药，还是安慰剂，给你治疗的主管医生也不知道；只有最初负责分配的试验人员知道，他们把这个分配的方案，藏在了一个火星人才知道的地方，等到试验顺利结束，最终要揭盲的时候，才拿出来。

● 所谓对照，最好理解了，要证明新药A好，必须找一个参照物。这个对照组一般是是目前已有的标准治疗。比如，PD-1抗体想要冲击肝癌的一线治疗，但是目前肝癌的一线治疗用药是索拉非尼，那么PD-1抗体必须做一个和索拉非尼头对头的III期临床试验，如果结果显示PD-1抗体的确更好，这样才能上市。但是，如果PD-1抗体希望被批准用于多线治疗后的胃癌，因为这种病人目前已经不存在标准治疗方案了，PD-1抗体只要和安慰剂（多半是盐水或者糖水）做比较，得出阳性的结果，那么就可以批准这个适应症了。