ESSENCE: Semaglutide and MASH Histology at 72 Weeks

The ESSENCE part 1 analysis established that, over 72 weeks, once-weekly semaglutide produced resolution of steatohepatitis without worsening of fibrosis in 62.9% of participants against 34.3% on placebo, and improvement in fibrosis by at least one stage without worsening of steatohepatitis in 36.8% against 22.4% 1. It did not establish fibrosis resolution, because the fibrosis endpoint counts a single-stage move on a five-point ladder, and it did not establish any clinical outcome, because those sit in the unfinished part 2. Fibrosis improvement and fibrosis resolution are different claims: the first means a biopsy read one stage lower than at entry; the second would mean no fibrosis at all.

This site covers how semaglutide acts at its receptor separately. This article leaves mechanism aside and dissects a histological endpoint that most coverage reports loosely, including the difference between resolution of steatohepatitis and a one-stage fibrosis change. It also marks what part 1 cannot show. Each section states its evidence tier.

Why MASH trials use paired liver biopsies

Evidence tier: regulatory guidance and histopathology methodology. Metabolic dysfunction-associated steatohepatitis is defined histologically: fat in hepatocytes, lobular inflammation and hepatocellular ballooning, with or without fibrosis. Imaging and blood tests can estimate fat and stiffness, but the disease-defining features, ballooning and inflammation, are read only on tissue. The scoring system used in trials was designed and validated by the NASH Clinical Research Network in 2005. It grades steatosis 0 to 3, lobular inflammation 0 to 2 and ballooning 0 to 2, sums them into an activity score, and stages fibrosis separately from 0 to 4 4.

The FDA's December 2018 draft guidance for noncirrhotic steatohepatitis with fibrosis sets out why biopsy sits at the centre of pivotal trials. Fibrosis is described as the strongest histological predictor of adverse clinical outcomes, including liver-related death. Because progression to cirrhosis takes years, the guidance names histological improvements that are reasonably likely to predict clinical benefit and can therefore support accelerated approval, and states that a trial designed to verify clinical benefit should be under way when the application is submitted 3. ESSENCE was built to that template: a 72-week histological analysis in part 1 and a 240-week clinical-outcome analysis in part 2 12.

ESSENCE design: population, fibrosis stages and randomisation

Evidence tier: human randomised trial, phase 3. ESSENCE is a two-part, multicentre, double-blind, placebo-controlled trial that randomised 1,197 adults with biopsy-defined steatohepatitis and fibrosis stage 2 or 3 in a 2:1 ratio to once-weekly subcutaneous semaglutide, at the dose approved for weight management, or placebo for 240 weeks 12. Part 1 is the planned interim analysis at week 72 in the first 800 participants randomised: 534 to semaglutide and 266 to placebo 1.

The baseline report for those 800 gives the population. 250 (31.3%) had fibrosis stage 2 and 550 (68.8%) stage 3. Mean age was 56 years, 57.1% were female, mean body-mass index was 34.6, and 55.5% had type 2 diabetes. Although cardiometabolic criteria were not an entry requirement, more than 99% met at least one 2. This is a population with clinically significant fibrosis, mostly at the stage immediately below cirrhosis, which is where the regulatory interest in fibrosis endpoints lies.

Co-primary endpoint one: resolution of steatohepatitis without fibrosis worsening

Resolution of steatohepatitis has a specific definition in the 2018 guidance: on overall histopathological reading, absent fatty liver disease or isolated steatosis without steatohepatitis, with an activity score of 0 to 1 for inflammation, 0 for ballooning and any value for steatosis; and no worsening of fibrosis on the NASH CRN fibrosis score 3. The endpoint is therefore about inflammation and cell injury, not fat and not scar. A liver can meet it while still steatotic and still fibrotic.

In ESSENCE part 1 this endpoint was met by 62.9% of the semaglutide group and 34.3% of the placebo group, an estimated difference of 28.7 percentage points (95% CI 21.1 to 36.2; P < 0.001) 1. The placebo rate deserves attention. One in three placebo participants met a resolution endpoint at 72 weeks. Some of that is genuine change under the trial's lifestyle advice and the 2.0% mean weight loss; some of it is the measurement noise discussed below. Either way, the drug effect is the 28.7-point difference, not the 62.9% headline.

Co-primary endpoint two: one-stage fibrosis improvement without steatohepatitis worsening

The second endpoint is improvement in fibrosis by at least one stage on the NASH CRN score, with no worsening of steatohepatitis, defined as no increase in the activity score for ballooning, inflammation or steatosis 3. In part 1 it was met by 36.8% on semaglutide and 22.4% on placebo, a difference of 14.4 percentage points (95% CI 7.5 to 21.3; P < 0.001). The combined endpoint, both resolution and fibrosis improvement in the same participant, was met by 32.7% against 16.1%, a difference of 16.5 points (95% CI 10.2 to 22.8) 1.

The fibrosis effect is about half the size of the resolution effect. That ordering is expected. Inflammation and ballooning respond to a changed metabolic environment within months; collagen remodelling is slower and the fibrosis stage is coarser. The guidance anticipates this by allowing sponsors to propose which histological change their mechanism should produce 3. A drug acting through weight and insulin sensitivity would be expected to show resolution first and fibrosis change second, which is what ESSENCE shows.

Why neither endpoint is fibrosis reversal

Fibrosis staging is ordinal. Stage 0 is none; stage 1 is perisinusoidal or periportal fibrosis; stage 2 is both; stage 3 is bridging fibrosis; stage 4 is cirrhosis 4. A participant entering at stage 3 who is read at stage 2 at week 72 has met the fibrosis endpoint. That participant still has clinically significant fibrosis. Reversal, in the sense the word carries in general usage, would mean a return to stage 0 or 1, and ESSENCE part 1 does not report that as an endpoint 1.

The language in secondary coverage drifts. Improvement becomes reversal; resolution of steatohepatitis becomes resolution of liver disease. Neither substitution is supported by the endpoint definitions. The accurate statement is that 14.4 more participants per hundred moved down one fibrosis stage on semaglutide than on placebo at 72 weeks, and that most of them started at stage 3 12.

Weight-dependent and weight-independent effects

Evidence tier: randomised comparison for the weight figures; post hoc, exploratory analysis for the rest. Mean body weight changed by −10.5% on semaglutide and −2.0% on placebo, an estimated difference of −8.5 percentage points (95% CI −9.6 to −7.4) 1. Hepatocytes do not express the GLP-1 receptor in validated human and primate tissue surveys 8, so there is no direct receptor pathway for the histological effect; it must run through weight, insulin sensitivity, lipid flux, inflammation or some combination.

A post hoc analysis of the same 800 participants, presented in November 2025, stratified histological response by weight change. Among participants who lost 2% or less of body weight, resolution of steatohepatitis without fibrosis worsening occurred in 48.4% on semaglutide and 25.8% on placebo (estimated difference 21.7 points; 95% CI 4.9 to 38.4). Fibrosis improvement in that stratum was 27.2% against 18.3%, with a confidence interval including zero (−6.1 to 22.9) 7. The sponsor describes these analyses as hypothesis-generating. Stratifying by a post-randomisation variable breaks the randomisation, so the strata are not comparable groups; the finding argues for a weight-independent component without measuring it.

Reader variability and the limits of biopsy scoring

Evidence tier: methodological studies of pathologist agreement. The scoring system's validation study reported inter-rater weighted kappas of 0.84 for fibrosis, 0.79 for steatosis, 0.56 for injury and 0.45 for lobular inflammation on 50 adult cases 4. Those were expert pathologists reading a curated set. In a 2020 study, three hepatopathologists independently read 678 digitised biopsies from 339 trial participants. Inter-reader weighted kappas were 0.609 for steatosis, 0.484 for fibrosis, 0.328 for lobular inflammation and 0.517 for ballooning. For the composite trial endpoints the unweighted kappas were 0.396 for resolution without worsening fibrosis and 0.366 for fibrosis improvement without worsening steatohepatitis. 46.3% of participants enrolled on one pathologist's reading were judged not to meet entry criteria by at least one of the other two 5.

Those figures describe the instrument ESSENCE used. Agreement of about 0.4 on the endpoints means a substantial fraction of endpoint classifications would change with a different reader. In a randomised trial this noise affects both arms equally and inflates the placebo response, which is one reason 34.3% of placebo participants met the resolution endpoint. It does not bias the between-group difference, but it widens confidence intervals and reduces power, and it makes individual-level claims about who responded unreliable 5.

Part 2 and the outcomes histology cannot predict

Evidence tier: pending. On 15 August 2025 the US Food and Drug Administration granted accelerated approval to semaglutide for noncirrhotic steatohepatitis with moderate to advanced fibrosis, on the basis of the part 1 histology. The agency's announcement states that additional data are required after approval to confirm the effect on a clinically meaningful endpoint, and that the trial will run to 240 weeks to determine whether the 72-week changes lead to fewer deaths, liver transplants and other liver-related events 6. The guidance that defined the endpoints also lists what those confirmatory outcomes are: progression to cirrhosis on histology, adjudicated hepatic decompensation events, a rise in MELD score from 12 or below to above 15, liver transplant and death 3.

The relationship between the histological surrogates and those outcomes has not been characterised; the 2018 guidance says so in terms 3. That is why the approval is accelerated rather than full, and why the agency's page describes continued approval as contingent on confirmatory evidence 6. Until part 2 reports, ESSENCE establishes a histological effect at 72 weeks and nothing about what that effect does to a patient's liver over years.

Where the evidence stops

ESSENCE part 1 established two things in a population of 800 adults with stage 2 or 3 fibrosis: that over 72 weeks, semaglutide against placebo increased by 28.7 percentage points the proportion whose steatohepatitis resolved without fibrosis worsening, and by 14.4 points the proportion whose fibrosis improved by at least one stage without steatohepatitis worsening 1. Both are surrogates a regulator has accepted as reasonably likely to predict clinical benefit 3. Both were read by pathologists using an instrument whose agreement on these very endpoints is around 0.4 5.

It has not established fibrosis reversal, which was not an endpoint; whether the effect is independent of weight, which only a post hoc analysis addresses 7; or any change in cirrhosis, decompensation, transplant or death, which is the business of part 2 6. A reader meeting a claim that semaglutide reverses liver scarring should ask which endpoint, in which stage, at which week. The answer, so far, is one stage, in 36.8% against 22.4%, at week 72.