Achieving positive topline results in a clinical trial marks a critical milestone in the drug development process, yet it is far from the end of the submission journey. Instead, it signals the start of a complex, fast-paced effort to prepare for regulatory submission and navigate the FDA’s multi-stage review. The final “regulatory defense” stage demands rigorous collaboration, meticulous planning, and adaptability to meet the expectations of regulatory agencies.

Here we discuss the key stages in the post-topline journey, exploring key milestones, unexpected challenges, and best practices for ensuring a strong submission and a smooth path to approval.

1. The Preparation: Post-topline readiness and strategic planning

The preparation phase begins immediately after topline results are available. During this critical window — often lasting several months — cross-functional teams shift their focus to assembling the final submission package. Statisticians and programmers play a central role here, finalizing the tables, listings, and figures (TLFs) that will populate the Clinical Study Report (CSR) and preparing submission-ready datasets following CDISC standards, including ADaM, SDTM, and associated documentation.

In parallel, a pre-BLA or pre-NDA meeting with the FDA is typically scheduled to align on expectations, identify potential concerns, and set the foundation for a smoother review process. This phase is not just about document generation; it’s about establishing a strategy, anticipating regulatory scrutiny, and ensuring the submission is both complete and compelling. The quality of the groundwork laid here often dictates the ease — or difficulty — of the phases that follow.

2. The Submission: Crossing the threshold to regulatory review

Once the submission is filed, the process transitions into a more structured phase governed by the FDA’s review protocols. The agency begins with a 60-day filing review to assess whether the BLA or NDA is complete and acceptable for full review. If so, the sponsor receives a Day 74 Letter, which provides early feedback, flags any immediate concerns, and confirms the Prescription Drug User Fee Act (PDUFA) date — typically 10 months post-filing for standard reviews or 6 months for priority reviews. Although this phase may seem procedural, its significance is high. A clean, well-organized submission can streamline the review process, limit questions, and reduce the risk of delays. This is also the point where rolling submissions, if applicable under Fast Track designation, can offer a tactical advantage by accelerating document delivery and potentially shortening review timelines.

For statistical and programming teams, this is not a time to sit back and relax — it’s an opportunity to ensure internal alignment and anticipate questions the FDA may raise based on known data complexities. Strong documentation and traceability within datasets and outputs are essential at this point, helping to support any needed follow-up. Proactive communication and readiness during this phase help lay the groundwork for the more intensive regulatory engagement that follows.

3. The Regulatory Defense: Responding, clarifying, and defending your data

The regulatory defense phase is where the bulk of agency interaction occurs — and where flexibility and responsiveness become essential. During this time, the FDA may issue multiple information requests (IRs), asking for clarification on statistical methodology, specific data points, or safety and efficacy outcomes. Mid-cycle communications, typically occurring around months 4–5 for standard reviews, offer a formal opportunity to assess the review’s progress and surface any significant concerns.

In some cases, the agency may convene an Advisory Committee (AdCom) meeting to gather expert input, particularly when there are outstanding safety questions or complex benefit-risk considerations. Throughout this phase, the ability to quickly respond to ad hoc requests, provide high-quality data outputs, and maintain close collaboration across functions is critical. It’s a high-stakes stage where well-prepared teams can help preserve timelines and ensure the submission stays on track.

4. The Unexpected: Adapting to setbacks and charting a new course

In some cases, the regulatory journey doesn’t lead directly to approval. If the FDA identifies significant deficiencies in the initial submission — whether related to clinical data, statistical interpretation, manufacturing, or safety — it may issue a Complete Response Letter (CRL). This marks a temporary halt in the process, requiring the sponsor to address the concerns before resubmission. Depending on the scope of the deficiencies, the resubmission may fall under Class I (minor issues, reviewed in 2 months) or Class II (major issues, reviewed in 6 months).

For statisticians and programmers, this could mean conducting additional analyses, integrating new data, or adjusting the structure and presentation of the submission package. While a CRL can be a setback, it’s also an opportunity to recalibrate, seek additional guidance from the FDA, and improve the likelihood of approval in the next cycle. The key is to approach this phase with transparency, strategic thinking, and a readiness to adapt and respond.

Final takeaways

The path from topline results to regulatory approval is rarely linear. Timelines can range from as little as 12 months in expedited reviews to over 30 months in cases involving major deficiencies and resubmissions. Success in this post-unblinding phase hinges on proactive planning, adaptable resourcing, and the ability to respond quickly and thoroughly to regulatory needs. Equally important is collaboration across functions — clinical, regulatory, biostatistics, programming, and operations must work closely and cohesively to anticipate challenges, align timelines, and respond efficiently to agency requests. Whether following a standard or accelerated route, the shared priority is a comprehensive, high-quality submission that stands up to regulatory scrutiny — and ultimately supports timely access to new therapies for patients.

Interested in learning more?

Watch Jasperlynn Kao and Florence Le Maulf’s recent webinar, “From Toplines to Triumph: Visualizing the Pathways to Regulatory Approval”:

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