The Nonclinical Podcast
Getting a drug to the clinic is hard. Understanding the nonclinical science behind it doesn't have to be. The Nonclinical Podcast breaks down toxicology strategy, IND preparation, and nonclinical development for biotech founders, scientists, and anyone who's ever sat in a meeting and wished they understood tox better. Hosted by Dessi McEntee, MS, DABT — a board-certified toxicologist who's been bringing new medicines to the clinic for over 15 years.
The Nonclinical Podcast
Your CRO Called It Adverse. Now What?
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The word "adverse" appears in your study report and the room goes quiet. Most founders treat it like a verdict. It isn't. It's a scientific conclusion — and it's one you need to own, understand, and be ready to defend when FDA asks about it. In this episode, we walk through the five-question framework for evaluating any toxicology finding, and explain the difference between a finding that limits your program and a finding that doesn't.
Key takeaways:
- "Adverse" is not a label your CRO assigns and walks away from — it's a scientific starting point that requires your interpretation and defense
- An elevated liver enzyme at the high dose might be adverse, or it might be an adaptive response — and that distinction directly determines your NOAEL and safety margin
- The five questions: Is there a dose response? Is it reversible? Does histopath confirm it? Is the magnitude biologically significant? Is it consistent across sexes and species?
- A non-adverse call requires just as much documented rigor as an adverse finding — "we don't think it's adverse" is not a regulatory argument
- An adverse finding doesn't kill your program. An adverse finding with no interpretation, no context, and no safety argument does
Links:
- The Complete Guide to Nonclinical Development: https://www.nonclinical.academy/
- Work with Dessi: dessimcentee.com
- Subscribe to the newsletter: https://the-nonclinical.com/
The Nonclinical is hosted by Dessi McEntee, MS, DABT — board-certified toxicologist and Fractional Head of Toxicology. Subscribe to the newsletter on LinkedIn, take the course at nonclinical.academy, or work with Dessi at toxistrategy.com.
Imagine opening this uh this multi-million dollar toxicology report for your biotech startup. And right at the top, I mean right in the executive summary is the word adverse.
SPEAKER_00Oh yeah. That is the nightmare scenario for so many leaders.
SPEAKER_01Right. For most founders and executives who are, you know, steering a new program toward clinical trials, seeing that word just feels like a complete death sentence. You instantly think your investigational new drug application, your IND is just doomed.
SPEAKER_00Which is exactly the tension we're exploring today. Because when you see that word on a report from your CRO, your contract research organization, the visceral response is always panic.
SPEAKER_01Absolute panic.
SPEAKER_00Right. You just assume the FDA will take one look at that label, see adverse, and basically shut your program down before it even reaches a human trial.
SPEAKER_01And that panic, honestly, is exactly why we're unpacking a really strategic curriculum today. We are doing a deep dive into a framework developed by Dessie McIntyre. She's a board certified toxicologist and a fractional head of toxicology.
SPEAKER_00Yeah, and her training program, the complete guide to non-clinical development, is our source material for this.
SPEAKER_01Exactly. And the mission for this deep dive is to show you why adverse is not uh it's not like a final verdict handed down by a judge. It's really just a scientific starting point, one that you, as a leader, need to own and actively defend.
SPEAKER_00Aaron Powell Which brings up the foundational mistake a lot of biotech executives make in this exact scenario. They totally surrender their analytical power to the CRO.
SPEAKER_01Aaron Powell Well, yeah, because it feels natural, right?
SPEAKER_00It does. But before we even get into the biology of what an adverse finding is, we have to establish who actually owns the interpretation of the data.
SPEAKER_01Aaron Powell Because I mean, the natural assumption for you as a sponsor is that the CRO ran the study, right? They collected all the data, they wrote the final report, so they must be the ultimate authority on what it all means. You literally hire them to be the experts.
SPEAKER_00It is an incredibly common assumption.
SPEAKER_01Yeah.
SPEAKER_00But legally and honestly scientifically, it's just incorrect. Aaron Powell Wait, really? Yeah. The CRO's mandate is actually surprisingly narrow. You have to think of them as a highly sophisticated data collection agency. Trevor Burrus, Jr.
SPEAKER_01Okay, so they just gather the raw numbers.
SPEAKER_00Right. Their job is to rigorously report what physically happened to the animals during the study. They record the weights, run the blood panels, log all the behavioral observations. Right. But they are not the final arbiter of what that raw data actually means for human safety. That interpretation and the regulatory defense of it belongs entirely to the sponsor.
SPEAKER_01It belongs to you.
SPEAKER_00Yes. To you and your toxicology strategist.
SPEAKER_01Aaron Powell It's uh it's kind of like taking your car to a mechanic, right?
SPEAKER_00Yeah.
SPEAKER_01The mechanic tells you the check engine light is on. That's the CRO.
SPEAKER_00That's a great way to look at it.
SPEAKER_01Aaron Powell But you're the one who has to figure out if the engine is actually going to explode, or if it just means you need like an oil change before a cross-country road trip, the FDA is going to ask you about the car, not the mechanic.
SPEAKER_00Aaron Powell Exactly. So if a CRO flags something as adverse, they're basically just noting a significant biological event happened. They aren't issuing a death sentence for your trial.
SPEAKER_01Aaron Powell Okay, so let's get into the specifics of that label then. Yeah. What actually defines an adverse effect in the eyes of the FDA?
SPEAKER_00So by regulatory standards, an adverse finding is a detrimental biological change that actively harms the health of the animal. It represents real damage or dysfunction.
SPEAKER_01Okay.
SPEAKER_00And crucially, it cannot simply be a physiological response to the drug being introduced.
SPEAKER_01Aaron Powell See that feels like a really fine semantic distinction to me. I mean, if a biological change happens strictly because I introduced a novel drug into a test subject, isn't that inherently detrimental?
SPEAKER_00Not necessarily. Uh think about the biology of intense physical exercise. Okay. If you go to the gym and lift incredibly heavy weights, your muscle tissue is going to ache. It swells up, it gets inflamed.
SPEAKER_01Usually for days.
SPEAKER_00Right. And if you ran a superficial diagnostic test on that muscle, it might say your tissue is under severe stress. But functionally, we know that's just an adaptive response.
SPEAKER_01Aaron Powell Because the muscle fibers are just adapting to handle the increased load. They're building mass.
SPEAKER_00Aaron Powell Exactly. Now compare that to, say, dropping a heavy barbell directly on your foot and tearing a ligament.
SPEAKER_01Ouch, yeah, totally different.
SPEAKER_00Trevor Burrus, Jr.: That is an actual detrimental injury. It's a failure of the system. So in toxicology, an adaptive response means the organism is just working harder to process the drug.
SPEAKER_01Aaron Powell Well, an adverse effect means the biological system is literally breaking down under the strain.
SPEAKER_00Aaron Powell Precisa.
SPEAKER_01That makes perfect sense. So let's translate that workout analogy into a pharmacological reality. How does that adaptive versus adverse dynamic actually show up in one of these CRO reports?
SPEAKER_00Aaron Powell Let's look at the liver. It's one of the most common organs to show stress in these studies.
SPEAKER_01Aaron Powell Sure. The body filter.
SPEAKER_00Trevor Burrus, Right. So say you have an animal on a very high dose of your compound and their liver gets physically heavier. On paper, the CRO flags increase liver weight. Okay. Now you have to interpret it. Is that weight increase adverse? As in, is the liver actively failing, taking cellular damage, swelling with fluid, or is it an adaptive response?
SPEAKER_01Aaron Powell Meaning the liver is just working overtime to metabolize this massive dose. So it's building more cellular machinery to handle the workload. It's like the muscle building mass.
SPEAKER_00Exactly. And proving that a finding is adaptive rather than adverse has massive tangible consequences for your entire development program.
SPEAKER_01Aaron Powell Because it changes the math.
SPEAKER_00It dictates your NOAL, your no-observed adverse effect level.
SPEAKER_01Aaron Powell Right. Because the NOAL is the mathematical anchor for literally everything that comes next. If you decide the liver is failing, you have to establish your NOAL at a much lower dose.
SPEAKER_00Down where the liver isn't taking damage, yes. Which gives you a very tight, highly scrutinized safety margin when you calculate your proposed starting dose for humans. Trevor Burrus, Jr.
SPEAKER_01The FDA is going to be watching you like a hawk.
SPEAKER_00Oh, absolutely. But if you can scientifically prove the finding is just an adaptive response, you can defend a much higher NOAL.
SPEAKER_01And that gives your clinical trials a way wider, more comfortable safety margin.
SPEAKER_00Exactly.
SPEAKER_01So the stakes are incredibly high. The CRO hands you this mountain of data, and you have to prove whether your drug caused a severe ligament air or just routine post-workout soreness. So how do you systematically build that defense? Because I mean, you can't just walk into the FDA and say, hey, trust us, it's just a workout.
SPEAKER_00No, you absolutely cannot do that. And this is where Mackinty's curriculum introduces a really rigorous five question framework.
SPEAKER_01Okay, let's walk through it.
SPEAKER_00To build a defensible narrative, you have to systematically interrogate the data. And the very first thing we have to isolate is the relationship between exposure and the biological event.
SPEAKER_01Question one.
SPEAKER_00Right. We have to look for a clear dose response.
SPEAKER_01Meaning, does the biological effect get mathematically worse as you increase the amount of drug given to the subjects?
SPEAKER_00Exactly. If a biological change is severe at your highest dose, but it completely drops off or disappears at your mid and low doses.
SPEAKER_01Then it's tied to the drug.
SPEAKER_00You've established a clear causal relationship. The drug is undeniably driving the change. That dose-dependent relationship is one of the strongest indicators that you're looking at a treatment-related effect.
SPEAKER_01But wait, let me push back on that premise for a second.
SPEAKER_00Go for it.
SPEAKER_01You're saying we only need to worry if the finding correlates perfectly with the escalating dose. But biology is incredibly noisy, right?
SPEAKER_00Very noisy.
SPEAKER_01So what if I have a control group? Animals that got zero drug, just a saline placebo, and they still show this exact same adverse finding? Or what if there's just a random massive spike in one isolated animal at the lowest dose?
SPEAKER_00All right.
SPEAKER_01If there's no clear dose response, do I just sweep that data under the rug so my drug looks safer to the FDA?
SPEAKER_00You never, under any circumstances, sweep data under the rug, ever.
SPEAKER_01Aaron Powell Okay, good to clarify.
SPEAKER_00If a finding is random or if it appears at similar rates in your control animals, it's almost certainly an incidental background finding.
SPEAKER_01Just the natural noise of biology. Trevor Burrus, Jr.
SPEAKER_00Completely unrelated to your drugs, but you must document it thoroughly in your submission. You have to explicitly explain the mathematical reasoning for why you consider it incidental.
SPEAKER_01So you have to show the FDA that you saw the anomaly on the radar, but then you show the math to prove why the anomaly isn't a threat.
SPEAKER_00Yes. You do not want to artificially handicap your own program by labeling a random quirk as a treatment-related adverse effect. Trevor Burrus, Jr. That makes sense. Trevor Burrus But the FDA demands transparency. You acknowledge the noise, explain the lack of dose response, and categorize it as incidental.
SPEAKER_01Aaron Powell Okay, but what if there is a flawless dose response? Like the high dose clearly causes a severe biological change, and the mid-dose causes a moderate change. Are we immediately trapped with an adverse label then?
SPEAKER_00Aaron Ross Powell Not necessarily. And this brings us to question two, the next critical layer of the investigation. Okay. Once we know exposure is driving the event, we have to figure out if the body can compensate over time. So we look at reversibility in the recovery animals. Aaron Powell Precisely. Reversibility is arguably one of the most powerful contextual tools you have.
SPEAKER_01Aaron Powell Because it shows if the damage is permanent.
SPEAKER_00Right. If you stop the drug exposure and the biological finding resolves on its own, that is incredibly meaningful data. It tells the reviewing pharmacologists at the FDA that the organism systems have the capacity to heal and return to baseline.
SPEAKER_01It's like a temporary side effect that washes completely out of the system once the drug clears.
SPEAKER_00Yes. But on the flip side, nonreversible findings signal something much more dangerous. I'd imagine so. If the finding persists long after the drug is gone, it means the compound has caused a permanent structural or functional change that the body just cannot repair. Wow. Yeah. If you have a non-reversible finding at your high dose, you can guarantee that the FDA is going to scrutinize your safety margins intensely.
SPEAKER_01Okay, so we've mapped out the overarching trends with the first two questions. Dose response tells us the drug is causing the issue, and reversibility tells us if the resulting injury is permanent.
SPEAKER_00Correct.
SPEAKER_01But those still feel like high-level trend lines. At some point, you can't just rely on systemic data, right? You have to actually look at the physical microscopic evidence inside the organism.
SPEAKER_00You do. And that is the critical next step. Question three. It's where many sponsors fail to connect the dots. You must correlate your clinical pathology with your histopathology.
SPEAKER_01All right, let's define those two terms clearly because they get conflated a lot in executive summaries. Clinical pathology is the macroscopic data, right? Like taking blood tests, measuring serum levels, weighing organs.
SPEAKER_00Exactly. Let's go back to the liver example. If the liver is stressed, it releases enzymes called AST and ALT into the bloodstream. Okay. Think of those elevated enzymes as a biological distress flare. Finding those elevated enzymes in a blood test is clinical pathology. Got it. Hastopathology, on the other hand, is the microscopic examination of the actual physical tissues by a specialized pathologist.
SPEAKER_01So to use a business operations analogy, I love these.
SPEAKER_00Go ahead.
SPEAKER_01Clinical pathology is seeing a massive spike in customer complaint tickets. You know the system is stressed. But histopathology is physically walking onto the manufacturing floor, opening up a machine, and seeing if the gears are actually stripped and broken.
SPEAKER_00That is a perfect way to conceptualize it. Because if your clinical pathology shows elevated AST and ALT distress flares in the blood, but your histopathology shows absolutely no microscopic lesions, no necrosis, no physical damage in the tissue itself.
SPEAKER_01Then you have a strong argument that the liver is just adapting to the workload. The machine is running hot, but the gears are intact.
SPEAKER_00Exactly. But if you look under the microscope and see actual cellular destruction.
SPEAKER_01Then the gears are broken.
SPEAKER_00Right. If you see something like centralobular hepatocyte degeneration.
SPEAKER_01Which means what? Exactly.
SPEAKER_00It essentially means the physical liver cells in the center of the hepatic lobe are actively dying and degrading. Oh wow. Okay. If you see that, then your distress flour was entirely accurate, the gears are fundamentally broken, and your argument changes entirely.
SPEAKER_01Right.
SPEAKER_00If you intend to call a systemic clinical finding non-adverse, your pathologist must provide a bulletproof microscopic argument showing that the physical tissues remain pristine and undamaged.
SPEAKER_01Which naturally leads us to evaluate the actual size and scope of the problem.
SPEAKER_00Yeah.
SPEAKER_01Because in biology, it's not just about identifying a change, it's about the magnitude of that change, which is question four.
SPEAKER_00Yes, magnitude.
SPEAKER_01And this is where I think executives, you know, who are used to looking at quarterly financial math, they get really tripped up by biological math.
SPEAKER_00It is a profound trap. Founders see a statistically significant p-value on a CRO report and instantly assume their program is facing a biological crisis.
SPEAKER_01Right, because the math says there's a deviation.
SPEAKER_00But in toxicology, statistical significance does not automatically equal biological importance.
SPEAKER_01Okay, let's unpack that logic. How can a number be mathematically significant but biologically irrelevant to the FDA?
SPEAKER_00Imagine a study where you observe a 12% increase in kidney weight in the animals receiving your drug.
SPEAKER_01Okay, 12%.
SPEAKER_00Mathematically, compared to your specific control group in that specific isolated study, that 12% is a statistically significant deviation. The math is real. But if you pull the historical background data for that exact species and strain of animal across hundreds of previous studies, you might find that a 12% fluctuation in kidney weight is entirely normal for that breed.
SPEAKER_01Oh, I see. So the math is accurate for this one isolated experiment, but zoomed out, the biological organism doesn't even care.
SPEAKER_00Exactly.
SPEAKER_01It's like an executive noticing that server traffic at their software company spiked by 12% on a Tuesday. Statistically, it's a measurable deviation from a normal Tuesday. But the servers are designed to handle a 50% fluctuation without breaking a sweat.
SPEAKER_00Right.
SPEAKER_01So operationally, that 12% spike means absolutely nothing.
SPEAKER_00That's it, exactly. It's a statistical reality, but not an operational crisis. Now, if server traffic spiked by 45% and it perfectly correlated with massive latency issues and user error reports, then the system is actively crashing. Yes. In toxicology, if you have a 45% change in kidney weight combined with a clear dose response and microscopic cellular death under the microscope, you have massive biological magnitude. The pathologist and the toxicologist have to synthesize all this data to determine if a mathematical change actually threatens the survival of the organism.
SPEAKER_01Okay, so a sponsor goes through this whole process. We've established a causal link with the dose. We've verified if the body can heal, we've matched the blood work to the microscopic tissues, and we verified that the magnitude is biologically threatening. Yes. The scientific argument is looking solid. Are we ready to submit the IND to the FDA?
SPEAKER_00Not yet. There's one massive final hurdle. Question five biological consistency.
SPEAKER_01Okay, what does that mean?
SPEAKER_00You have to interrogate the data and ask, is this finding consistent across different sexes and across different species?
SPEAKER_01Oh, right, because biological systems are wildly complex, and you might see severe toxicity in a male rat, but absolutely no reaction in the female rats.
SPEAKER_00Or your rat studies show massive organ failure, but your dog studies are totally clean and healthy.
SPEAKER_01Right. And you can't just point to the clean dog study in your submission and say, hey, look, it's fine in dogs, so we're good to go.
SPEAKER_00No, the FDA expects you to explain exactly why that discrepancy exists.
SPEAKER_01So what are the actual mechanisms driving those differences? Like why would a drug ravage a male test subject but leave a female completely unharmed?
SPEAKER_00Often it comes down to deep metabolic differences. For example, female rats possess different levels of certain cytochrome P450 enzymes in their livers compared to males.
SPEAKER_01Okay, and what do those enzymes do?
SPEAKER_00They are responsible for metabolizing and clearing drugs from the bloodstream. Oh. So if a female rat processes a compound much slower due to her specific enzyme profile, the toxic metabolites might build up in her system and cause damage.
SPEAKER_01Well, a male rat with a different enzyme profile might metabolize and excrete it rapidly before it does any harm.
SPEAKER_00Precisely.
SPEAKER_01So the female simply lacks the metabolic machinery to clear the drug fast enough. And I'd imagine the same mechanism applies across species. A rat might process a drug entirely differently than a dog and obviously differently than a human.
SPEAKER_00Or it could be about target receptors. The drug might mind to a specific cellular receptor that exists in a rat, but that receptor doesn't even exist in a dog's biology.
SPEAKER_01So the biological mechanism driving the toxicity might be entirely absent in one species.
SPEAKER_00Exactly.
SPEAKER_01But let me pose a realistic scenario here.
SPEAKER_00Okay.
SPEAKER_01What if a founder is staring at a bizarre, sex-specific toxicity in their CRO data, and their team truly does not know the mechanism? Like they don't have the granular P450 enzyme data, they don't know the receptor expression levels. Do they just, you know, take their best educated guess in the IND submission to keep the timeline moving?
SPEAKER_00If you guess, the FDA's reviewing pharmacologists will dismantle that argument instantly.
SPEAKER_01Really? Instantly. Oh yeah. If you cannot clearly scientifically explain the biological pattern, the FDA will simply mandate that you go back to the lab and figure it out before they allow human trials. Yeah. Using we don't know as a justification for why a toxic finding isn't relevant to human safety is the Yes.
SPEAKER_00We don't know usually results in an immediate clinical hold. And this highlights exactly why an executive needs a specialized toxicology strategist to synthesize this data.
SPEAKER_01You can't just wing it.
SPEAKER_00You have to connect the dots across species, across sexes, and across metabolic profiles to build a proactive, bulletproof narrative. You cannot just act as a courier passing the CRO's raw data to the FDA and hoping they figure it out for you.
SPEAKER_01All right, so let's move to the execution phase. You've interrogated the data using this entire five-question framework. You've looked at dose, reversibility, tissue correlation, magnitude, and consistency.
SPEAKER_00You have your conclusion.
SPEAKER_01Right. So how do you actually structure this argument in the IND submission? Let's assume you've done all the rigorous math and the finding truly, undeniably, is adverse.
SPEAKER_00The most critical takeaway here for any biotech executive is this an adverse finding does not inherently kill your program.
SPEAKER_01See, that feels incredibly counterintuitive to me. If you are formally admitting to the FDA that your drug causes structural damage to an organism, how does the program survive?
SPEAKER_00Because the FDA fully expects to see toxicity at maximum doses. That is the entire point of running toxicology testing in the first place, to find the breaking point.
SPEAKER_01Oh, right. You're intentionally trying to break the system.
SPEAKER_00Exactly. What kills programs is an adverse finding that lacks context. Your safety argument in the IND must be incredibly transparent and meticulously reasoned. You outline the exact biological mechanism driving the toxicity. You define the specific dose at which it occurs.
SPEAKER_01You present the reversibility data to show if it heals.
SPEAKER_00Yes. And then crucially, you explain exactly what this means for your proposed human clinical dose, mathematically proving that you still have an adequate safety margin.
SPEAKER_01So you're basically going to the FDA and saying, look, yes, this drug causes a biological fire at a massive dose, but we know exactly how the fire starts, we know the body can put it out, and most importantly, we are dosing humans so incredibly far below that threshold that the fire will never ignite.
SPEAKER_00That is exactly it. You are presenting a deeply understood, highly managed risk. But here is the flip side, which is equally important for executives to grasp.
SPEAKER_01Okay, what's that?
SPEAKER_00What if you go through this entire analytical framework and confidently determine that the CRO overcalled it and the finding is genuinely non-adverse? It's just an adaptive response.
SPEAKER_01Well then you correct the label to non-adverse in your executive summary, you document the change and you move forward, right?
SPEAKER_00No. And this is where many smart sponsors fail.
SPEAKER_01Wait, why?
SPEAKER_00A non-adverse call requires the exact same level of extreme scientific rigor as an adverse call.
SPEAKER_01Really?
SPEAKER_00Yes. You cannot just change the label in your submission and expect the FDA to take your word for it. A non-adverse call that isn't robustly defended with data is just as problematic as an unexplained adverse finding.
SPEAKER_01Wow, that is a fascinating irony. So basically, marking a biological event as safe without proving the mechanism is just as dangerous to your IND timeline as having a toxic finding.
SPEAKER_00Exactly.
SPEAKER_01Whether the data looks good or bad, you have to walk the FDA through the exact same dose response, histopathology, and consistency arguments to prove why it's not adverse.
SPEAKER_00You have to show all of your scientific math. The regulatory expectation of rigor doesn't vanish just because the outcome happens to be favorable to your business goals.
SPEAKER_01That makes a lot of sense.
SPEAKER_00And this is exactly the level of strategic execution that Desi McInty's curriculum is designed to instill in biotech teams.
SPEAKER_01Right, because her training spans study design, species selection, and these highly complex IND defense strategies.
SPEAKER_00Aaron Powell Precisely because getting this wrong is catastrophically expensive in terms of time and capital.
SPEAKER_01I mean, the cost of training a scientific team on this framework is essentially a rounding error compared to the cost of a six-month clinical hold because a sponsor mismanaged the safety argument.
SPEAKER_00It is the absolute difference between a program advancing to the clinic and a program dying quietly in the lab.
SPEAKER_01So as we wrap up this deep dive, let's crystallize the core takeaway for you as a founder or executive. When that massive toxicology report lands on your desk, remember the operational dynamic. The CRO is the data collector. Their job is strictly to report the physiological events that occurred in the study. Your job is to interpret what those events mean for human safety. The gap between those two responsibilities is exactly where INDs either get approved or placed on clinical hold.
SPEAKER_00No, but by systematically applying this analytical framework, you know, by ruthlessly interrogating dose response, reversibility, microscopic tissue evidence, biological magnitude, and mechanistic consistency, you regain total control of your non-clinical data.
SPEAKER_01You don't have to be paralyzed by the CRO's initial label.
SPEAKER_00Exactly. You can construct a rigorous, defensible scientific argument.
SPEAKER_01Which brings us to a final thought I want to leave you with today. We started by talking about the pure panic that sets in when you first see the word adverse on a million-dollar lab report. But if adverse isn't a final binary verdict and is instead just the starting point for a complex biological negotiation, how many viable, incredibly promising, life saving drugs have been abandoned early, simply because an executive saw the word adverse in a CRO summary and didn't realize they had both the power and the scientific responsibility to argue otherwise.
SPEAKER_00A sobering thought.
SPEAKER_01It really is. So don't let a raw data report be the end of your clinical ambitions. Synthesize the science, build the argument, and show your work.