Information Regarding Explanations to Driver Mutations in the Development of Anti-cancer Drugs — PMDA Early Consideration Summary

In Plain Language

The document explains what evidence to present when a developer claims that a particular genetic change is a “driver mutation” relevant to an anti-cancer drug. This matters because, although confirmatory phase III studies usually evaluate efficacy and safety using an endpoint such as overall survival, some drugs may be approved on clinical data from earlier development, including tumor responses in phase II studies. PMDA says that a claim about a driver mutation should be supported by a reasoned explanation of its biological significance in the relevant cancer, alongside early clinical study results. The explanation should address whether the altered gene is expressed as a protein, whether the alteration can produce cancer-like properties, and whether evidence supports a causal role in cancer development. For development spanning different cancer types, the document also highlights the importance of examining biological similarities and differences between those cancers.

What This Guidance Covers

The document concerns explanations about driver mutations in the development of anti-cancer drugs. Its stated setting is PMDA clinical trial consultations and applications for approval. It addresses what a consulter or applicant should explain when claiming that a mutation is relevant as a driver mutation, particularly where the claim rests on a one-to-one relationship between the mutation and cancer development. The document also discusses development of anti-cancer drugs across cancer types, where the same genetic alteration may be considered in more than one cancer type or organ.

The focus is the scientific and tumor-biological reasoning behind the claim, considered together with results from clinical studies at the early stage of development. The document gives examples of evidence and specific experimental models, but it does not present those examples as a complete list of mutations or cancer types. It also does not set out a statistical analysis plan, a clinical endpoint definition, or a numerical threshold for deciding whether an alteration qualifies as a driver mutation.

The background includes situations involving orphan drug designation. It notes that explanations about driver mutations may affect consideration of whether a target disease represents “salami slicing.” The document describes the relevant situation as one in which the total number of patients with the target disease is more than 50,000, but treatment is applicable only to a limited population based on biomarkers, provided the limitation is scientifically sound—for example, where a target-protein expression level or genetic alteration is biologically significant. This is background to the document’s purpose, rather than a separate detailed procedure for designation.

Why It Matters

The document responds to the different kinds of evidence that can arise during anti-cancer drug development. It describes phase III confirmatory randomized controlled studies, generally using a primary endpoint such as overall survival, as the usual way to demonstrate efficacy and safety. But it also notes that some drugs may be approved based on relevant clinical data from exploratory studies corresponding to phase II when high clinical utility is expected. For rare molecular subtypes, a confirmatory randomized controlled study using overall survival as the primary endpoint may be difficult to conduct, and some drugs’ efficacy may be primarily evaluated through tumor response in a phase II study.

In that setting, an explanation of why a genetic alteration is important to cancer biology can be relevant to how developers describe the rationale for a drug and its target population. PMDA points out that not every mutation found in a cancer-related gene should be classified as a driver mutation. Mutations can accumulate as part of a multi-step process, and their contribution to cancer development and progression depends on the gene’s function and the role of the alteration. A claim therefore needs a scientific rationale, rather than relying only on the presence of an alteration in a tumor or on a general label.

Key Recommendations

1. Explain the biological basis for the driver-mutation claim. When a consulter or applicant claims that a mutation is relevant as a driver mutation because of a one-to-one relationship between the mutation and cancer development, PMDA considers that all the points described in sections 3.1 to 3.3 should be adequately explained as evidence for tumor biology. The document recommends consultation with PMDA as necessary when planning the development program and considering whether an alteration is relevant as a driver mutation.

2. Describe expression of the protein produced from the altered gene. Explain the expression of proteins derived from the gene with the aberration in the indicated cancer types. The document connects genetic abnormalities with quantitative or qualitative changes in the translated protein and with the acquisition of malignant characteristics. As an example, it reports that 3% to 5% of patients with non-small-cell lung cancer (NSCLC) have an ALK fusion gene, detected by methods such as fluorescent in situ hybridization (FISH) or immunohistochemical staining (IHC).

3. Explain how the alteration can produce cancer-related properties. Describe how the genetic aberration may act as an oncogenic factor in the indicated cancer type. The document suggests addressing whether introducing the altered gene into normal cells produces malignant phenotypes, such as anchorage-independent growth or enhanced proliferation, and whether tumors form after those cells are transplanted into immunodeficient mice. Its example describes EML4-ALK gene fusion introduced into murine fibroblasts: the cells showed loss of contact-inhibition, and transplanted cells led to tumor development in nude mice.

4. Address the causal relationship between the alteration and cancer development. Discuss how the genetic aberration targeted by the drug contributes to cancer development and progression without being affected by other factors. The document gives as an example whether tumors form in normal tissues or organs corresponding to the indicated cancer type in a model such as an animal genetically modified to express the driver mutation. It describes disease-model mice in which a single gene abnormality considered to cause cancer in a specific tissue is produced using, for example, a tissue-specific or drug-inducible promoter.

5. For development across cancer types, examine each cancer and the basis for a shared rationale. The document says it is important to obtain as much data as possible about tumor-biological differences between the target cancer types, consider those differences from multiple perspectives, and rationally explain why the driver-mutation claim applies across cancer types. It notes that information about the role of the genetic aberration in carcinogenesis in each cancer type, and the basis for common biological significance among cancer types, can be useful in clinical development.

Practical Implications

Interpretation: Developers preparing a rationale for a mutation-targeted anti-cancer drug can use the document’s three evidence areas to organize the biological case. The point is not simply to name a mutation, but to connect the genetic alteration to the relevant cancer type and explain the supporting evidence. The document also emphasizes presenting that biological explanation together with early-stage clinical study results; biological experiments and clinical findings address related but distinct parts of the rationale.

For nonclinical teams, the examples indicate the kinds of questions the explanation may need to address: whether the gene alteration is present and expressed in the indicated cancer, whether it can produce malignant characteristics in cells, and whether a suitable model supports a causal role in tumor formation. The specific examples in the document include cell transformation experiments and genetically modified animals; they illustrate evidence types, not a claim that every development program must use those exact models.

For clinical and regulatory teams, the document’s discussion is relevant when development relies on earlier clinical results, such as tumor response in a phase II study, and the mutation is central to explaining the treatment population. If the proposed population spans multiple cancer types, the rationale should address both the role of the alteration in each cancer and the basis for treating its biological significance as common across them. The document recommends seeking PMDA consultation as necessary when considering the relevance of a mutation as a driver mutation during development planning.

Technical Details

Meaning of “driver mutation” in this document. The document first describes the broader use of the term: among mutations in cancer-related genes, mutations particularly important to cancer development are called driver mutations. It then explains that there is no clear definition based simply on a mutation having a significant contribution to cancer development. For this Early Consideration, PMDA refers to mutations that can be determined to have high scientific and rational clinical utility from a tumor-biological point of view in anti-cancer drug development.

More specifically, PMDA says the term refers to mutations for which the degree of oncogene addiction is high and drug efficacy can reasonably be predicted by evaluating the results together with clinical studies at the early stage of development. In everyday terms, oncogene addiction describes a situation in which a cancer’s continued growth or survival is strongly dependent on a particular cancer-promoting alteration. This explanation is for understanding the term; the document does not provide a numerical measure or threshold for “high” oncogene addiction.

The definition does not mean that every mutation found in a cancer-related gene is a driver mutation. The document describes cancer development, particularly in solid tumors, as generally involving the accumulation of mutations or epigenetic mutations in multiple genes, with the contribution of each alteration depending on the gene’s original function and role in carcinogenesis. It distinguishes that multi-step pattern from cases in which the cause and result have a one-to-one relationship. As examples of alterations considered highly mutually exclusive and strongly oncogenic in isolation, it names ALK fusion genes and ROS1 fusion genes. However, PMDA expressly says it has not concluded that a driver mutation can be identified only when there is a one-to-one relationship. A claim still needs a rational scientific explanation based on tumor biology.

Three evidence areas, in sequence. First, describe protein expression from the altered gene in the indicated cancer type. The document’s example is ALK fusion gene expression in NSCLC, with detection by FISH or IHC among the methods mentioned. Second, explain the effect of the alteration on cancer development, including evidence that introducing it into normal cells can lead to malignant phenotypes or tumor formation after transplantation. Third, discuss whether the alteration itself contributes causally to cancer development and progression, using evidence such as tumors forming in a relevant tissue in a model that expresses the alteration.

The animal examples illustrate the third area. The document describes lung adenocarcinomas developing in mice engineered to express EML4-ALK in lung alveolar epithelial cells, and lung tumors in mice expressing certain ROS1 fusion genes in those cells. It also describes lung tumors in conditional knock-in mice expressing a HER2 exon 20 insertion mutant following doxycycline administration. These examples show how tissue-specific or inducible expression can be used to investigate whether an alteration contributes to tumors in a relevant organ; they do not establish that one model or one result alone settles every driver-mutation claim.

For development across cancer types, the biological rationale needs to account for the role of the alteration in carcinogenesis in each cancer type and the evidence supporting common biological significance across types. PMDA calls for as much data as possible on biological differences between the target cancer types and consideration of those differences from multiple perspectives. The explanation should therefore make clear both what is shared and what may differ between the cancers under development.

Who Should Read It

This document is relevant to anti-cancer drug sponsors and development teams making a driver-mutation claim in a PMDA clinical trial consultation or an application for approval. It may be particularly useful to regulatory affairs professionals preparing the scientific rationale, clinical teams interpreting early-stage study results, and nonclinical scientists generating or evaluating tumor-biology evidence. Statisticians and medical writers may also find it useful when helping teams keep the biological rationale distinct from clinical evidence and explain how each supports the development program. It is especially pertinent when early clinical data inform development in a rare molecular subtype or when a drug is being developed across more than one cancer type.

Official PMDA Source

• Official title: Information Regarding Explanations to Driver Mutations in the Development of Anti-cancer Drugs (Early Consideration)
• Issuing body: Pharmaceuticals and Medical Devices Agency, Office of New Drug Ⅴ
• Date on cover: June 17, 2026
• Official PMDA PDF: View the PMDA document
• PMDA Early Consideration list: View the PMDA list page

Source: Pharmaceuticals and Medical Devices Agency (PMDA) website, PMDA list page. This page was created by editing and summarising the PMDA document.

Consult the official document; this summary does not replace it. PMDA provides the English version for reference, and the Japanese original prevails if the two differ. PMDA describes Early Consideration documents as reference information reflecting its views at the time of publication, which may change as scientific knowledge develops.

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