In the metformin PMP webinar on September 22, 2026, Dr. Oliver Eng of UC Irvine answered patient questions about his trial of metformin for pseudomyxoma peritonei (PMP). He covered who can join, the five in-person visits, cost, side effects, and whether patients taking palbociclib or a KRAS inhibitor can join.

I hosted the session and Renee Hill, who sits on the Appendicure board and is a mucinous adenocarcinoma survivor herself, ran the questions. Most of them came from you, sent in ahead of time or typed into the chat while he was talking. Dr. Eng is a surgical oncologist at UC Irvine who treats people with appendix tumors and PMP, and he is the principal investigator on the trial.

If you want the background on the trial first, including the lab research behind it, I wrote about that in Why a Cheap Diabetes Pill Is Now Being Tested Against PMP.

Watch the full webinar

The full recording is below if you’d rather hear Dr. Eng answer the questions himself.

How the trial works

The trial is registered as NCT07693452. Everyone who joins takes metformin, a common diabetes pill. The trial listing gives the dose as 850 mg by mouth once a day. There is no placebo. You stay on it for up to 18 months, with scans at the start and then every six months.

The main thing the study measures is whether people can actually stick with it. The goal is for patients to take at least 80 percent of their doses over the first six months. Dr. Eng was clear that this is a first step. The team will also track whether the disease grows, stays the same, or shrinks, but a small study like this is mostly built to answer whether the treatment is doable.

At the September 22 webinar, the target was 15 patients. He said that number could grow depending on how enrollment goes, so reaching 15 doesn’t automatically close the trial. He couldn’t share how many people had enrolled. He did say several more patients were lined up to start over the next month or so, and that he hopes to know a lot more in about a year.

Who can join, and who can’t

The trial is for adults with PMP that is believed to come from an appendiceal mucinous neoplasm. That means a LAMN or HAMN, short for low-grade or high-grade appendiceal mucinous neoplasm. You also have to fit one of these situations. Your disease came back or didn’t respond after cytoreductive surgery (CRS) and HIPEC, which is heated chemotherapy delivered into the abdomen during surgery. Or your surgeon has said the disease can’t be removed. Or CRS and HIPEC are not currently planned.

You can’t join if your disease can be removed and CRS and HIPEC are planned. You also can’t join if you already take metformin for something else, like diabetes, or if you’ve had a bad reaction to it before. The trial listing also requires that you be well enough to take care of yourself and be up and about for more than half your waking hours.

These are the main criteria discussed during the webinar. The study team has to review your diagnosis, medical records, and overall health to confirm whether you’re eligible.

Several people asked why mucinous adenocarcinoma isn’t included. Dr. Eng said the lab work behind this trial was done on mucinous neoplasms, not adenocarcinoma, and those are different diseases. He didn’t rule out opening this trial or a new one to adenocarcinoma later, but for now it isn’t enrolling those patients. He added that UC Irvine has other trials, both surgical and drug trials, for people with adenocarcinoma that has spread to the lining of the abdomen, and that a consultation there could look at those.

This trial does not include mucinous adenocarcinoma, goblet cell adenocarcinoma, signet ring cell disease, non-mucinous adenocarcinoma, or appendiceal neuroendocrine tumors.

Getting started: consults, referrals, and travel

The first step is a consultation with Dr. Eng to talk through the trial. It can be done by video. If you live in California, you can book that video visit directly. If you live in another state, UC Irvine needs a second-opinion referral from your own doctor before they can see you by video. Renee pointed out that these rules come from state laws and insurance, and they vary a lot from state to state.

Dr. Eng said he lets the clinical trials team know ahead of time when someone is coming in about the trial, so they’re usually ready to answer questions at that first visit. If you want to go ahead, you may even be able to sign the consent form that same day, and consent can be done virtually. From there, it usually takes somewhere between a week or two and several weeks to actually start. “It’s not months,” he said.

Once you start, you have to come to UC Irvine in person five times. That’s day one, about one month later to see how you’re handling the drug and check bloodwork, and then at 6, 12, and 18 months. Someone asked if a patient in Seattle would have to fly to California just for the first consult. The answer is no. The consult and consent can happen online. The in-person visits start when treatment starts.

You can get your scans done near home and have them sent to UC Irvine for their radiologists to review. That should cut down on some of the burden for people who live far away.

What it costs

The metformin itself is free. The clinic visits, bloodwork, and scans are treated as regular medical care and billed to your insurance. As of the September 22 webinar, there was no travel funding. Dr. Eng said their social workers can help look for support, but at that point the drug was the only thing the trial paid for.

Side effects, blood sugar, and life after CRS

The side effects people report most with metformin are nausea, diarrhea, and vomiting. Some people get headaches or feel weak. Dr. Eng said the drug is generally safe and well tolerated, and the team asks patients to take it with food. Patients get a printed list of possible side effects, and the team watches for them closely.

Someone in the chat asked whether metformin lowers blood sugar in people who don’t have diabetes. Dr. Eng described the study dose as low and said the chance of a substantial drop in blood sugar was low. The team checks bloodwork and monitors how patients tolerate treatment, including at the one-month follow-up.

Renee asked a question that many survivors of this surgery have. Many people already have stomach and bowel problems after CRS and HIPEC, and metformin’s side effects are mostly in the gut. Dr. Eng said the team does monitor for this, but that bowel problems after surgery have a lot of different causes. They depend on how much bowel was removed, how you’ve recovered, and how well you absorb food. For problems tied to your own surgery, like an ostomy or drains, he said to go back to the team that did your surgery. He recommended care at a center that has dietitians, physical therapists, and palliative care on the same team, because these services can help with recovery.

Other treatments during the study

Dr. Eng said UC Irvine’s pharmacy found no known major interaction between metformin and palbociclib (Ibrance), and that taking palbociclib does not automatically prevent enrollment. He said the same about KRAS inhibitors, speaking about them as a group without naming specific drugs. A pharmacy team follows trial patients along with the doctors. The trial team’s doctors and pharmacists need to review your specific medications before you enroll.

Why metformin, and what mitochondria have to do with it

One of the first questions sent in asked whether appendix cancer is a mitochondrial disease. Mitochondria are the tiny parts inside most cells that turn food into energy. Dr. Eng said these diseases are not currently understood to be primary mitochondrial disorders. His team’s research suggests that these tumors may use one of the cell’s normal energy processes, which happens in the mitochondria, to survive and grow in the abdomen. That process is called oxidative phosphorylation.

Metformin is known to act on that process. Dr. Eng said scientists still debate exactly how metformin works, even now, but it does affect this pathway. His team chose it because it has been around for decades, it’s easy to get, and it has a long safety record across many doses. Renee noted that using a drug that already exists can move the science along faster than building a new one.

Another person asked if there are medicines that raise or lower oxidative phosphorylation. He said there are many, but this is a normal process that happens all over the body, so it isn’t as simple as picking a pill. He treated it as an open research question.

Near the end, someone asked whether the hope is that metformin slows disease people already have, or that it keeps it from coming back. “I hope both,” he said. He was also candid that nobody knows yet. “Clinical trials are clinical trials for a reason,” he said. This study is first checking whether people can take it, and then looking at how the disease responds.

If someone’s disease grows while they’re on the trial, they usually come off the drug. He said there is some room to talk that through with the doctors running the trial, but stopping is the norm. Renee asked whether a small first trial like this could lead to a bigger one. He said that depends completely on what the data shows. If it doesn’t work, there’s no reason to run a bigger trial.

Bigger questions beyond the trial

What to look for on your pathology report

Renee asked which parts of the pathology and surgery reports people should ask their doctor about. Dr. Eng said to start with the diagnosis. Pathologists look at the tissue under a microscope and run stains, and from that they can tell what kind of tumor it is. Ask whether the diagnosis is an appendiceal mucinous neoplasm, such as LAMN or HAMN, or an invasive adenocarcinoma. Also ask about the tumor’s grade and whether it has spread. Reports describe grade in different ways depending on the tumor type, so ask your oncologist to explain what the wording on your own report means. He said these details together shape the treatment plan.

Getting an expert opinion when your local team hasn’t seen many cases

One person asked how to get an expert opinion when their local oncologist has rarely treated appendix cancer. Dr. Eng encouraged people to get at least a consultation at a center that treats a lot of appendix tumors, because the disease is rare and there are several different ways to treat it. He said UC Irvine can provide a consultation and communicate with the patient’s local team, so patients do not have to travel there for all their care. Some online services also set up second opinions with academic centers, though insurance can limit those. If you’re weighing that step, I wrote about it in When “Unresectable” Isn’t the Final Word in Appendix Cancer.

The Godfrey guidelines

I asked what he thinks of the Godfrey guidelines, the 2025 expert consensus from the Peritoneal Surface Malignancy (PSM) Consortium, compared with the NCCN guidelines. He said the consortium’s guidelines grew out of work by Dr. Kiran Turaga and colleagues at Yale, who brought together peritoneal surface experts from across the country to update the Chicago Consensus Guidelines published in 2020. He said the two groups talk to each other, and that guidelines keep changing as new data comes in, sometimes month to month. He added that the consortium wrote them for doctors, patient advocates, and patients to use.

The MD Anderson chemotherapy study

A lot of you have been asking about the new MD Anderson paper on chemotherapy after surgery, especially when a local hospital is recommending chemo anyway. Dr. Eng didn’t weigh in on that specific paper. He said that with rare cancers, even expert centers sometimes manage the same situation differently, because there isn’t enough data to settle every question. His advice was that if you want another opinion, get one. I covered what that study did and didn’t look at in Appendix Cancer Chemotherapy After Surgery.

Questions from the metformin PMP webinar

Who can join the metformin PMP trial?
Adults with PMP from a LAMN or HAMN whose disease came back after CRS and HIPEC, can’t be removed, or for whom CRS and HIPEC are not currently planned. Mucinous adenocarcinoma and other appendix cancer subtypes are not included. The study team confirms eligibility after reviewing your records and overall health.

Do I have to travel to California?
The first consultation and the consent may be done virtually. Dr. Eng said patients outside California need a second-opinion referral from their local doctor first, and UC Irvine can confirm the arrangements for your location. Taking part in the trial requires five in-person visits over 18 months. Scans can be done near home and sent in.

How much does the trial cost?
The metformin is free. Visits, labs, and scans are billed to your insurance. As of September 22, 2026, there was no travel funding.

Can I take palbociclib or a KRAS inhibitor while on the trial?
Dr. Eng said taking palbociclib does not automatically prevent enrollment, and he said the same about KRAS inhibitors. The trial team’s doctors and pharmacists review each patient’s medications before enrollment.

Can patients outside the U.S. join?
Dr. Eng said there has been international interest, but participation would need to be explored with UC Irvine’s international patient team. He did not confirm whether any particular international patient could enroll.

Should I ask my doctor for metformin instead of joining?
Nobody knows yet whether metformin helps PMP. That’s what the trial is for. Talk to your own oncologist before starting any new drug.

How do I contact the study team?
Email ucstudy@uci.edu or call 877-827-8839. The trial and others open for appendix cancer and PMP are also on the Appendicure trial finder.

Thank you to Dr. Eng for giving this community his time and answering patient and caregiver questions, and to Renee for running the session. At the end he thanked the patients and advocates who give their time to this work, and I’ll pass that thanks along to everyone who sent in a question.

Sources: Appendicure webinar with Dr. Oliver Eng, UC Irvine, September 22, 2026, moderated by Renee Hill. ClinicalTrials.gov record NCT07693452, last updated July 2026, for dose, endpoints, and eligibility criteria. This post reports what Dr. Eng said in a group Q&A. It is not medical advice for any one person.