Retifanlimab: A PD-1 Antibody for Anal Cancer and Merkel Cell Carcinoma

Table of Contents

1. What Retifanlimab Is
2. How a PD-1 Blocking Antibody Works
3. Two US Approvals and Their Dates
4. The POD1UM-303/InterAACT 2 Trial in Advanced Anal Cancer
5. Retifanlimab Alone After Platinum Chemotherapy
6. The Merkel Cell Carcinoma Results
7. How the Label Gives the Drug
8. Immune-Mediated Side Effects and Their Rates on the Label
9. Infusion Reactions, Transplants, Pregnancy and Breastfeeding
10. What Is Not Known
11. Key Research Papers
12. Connections
13. Featured Videos

What Retifanlimab Is

Retifanlimab is a monoclonal antibody — a single, precisely copied immune protein made in cell culture. The US prescribing information describes it as a humanized immunoglobulin G4 kappa antibody, produced in Chinese hamster ovary cells, with a molecular weight of about 148 kilodaltons. “Humanized” means that most of the protein has been engineered to look like a human antibody, so the body is less likely to treat the drug itself as foreign. The first human study described it as “hinge-stabilized,” a small change in the antibody’s structure that keeps the molecule in one piece.

Its official US name carries a four-letter suffix, retifanlimab-dlwr. The US Food and Drug Administration adds such meaningless suffixes to the names of biological drugs so that products that are alike, but not identical, can be told apart in records. The ending -mab marks it as a monoclonal antibody.

The drug comes as a liquid concentrate of 25 mg per mL in a single-use vial holding 500 mg, which is diluted and dripped into a vein. It is not a pill and is not given at home.

Retifanlimab belongs to the same family as several older PD-1 and PD-L1 blocking antibodies used in melanoma, lung cancer and many other cancers. The research on those drugs, and on the Nobel-winning work that led to them, is covered on the Allison and Honjo page and the Melanoma Immunotherapy page.

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How a PD-1 Blocking Antibody Works

T cells are the white blood cells that recognize and kill infected or abnormal cells. Because an unchecked T cell can also damage healthy tissue, the body equips T cells with “checkpoint” receptors that switch them down. One of these is programmed death receptor-1 (PD-1). When PD-1 on a T cell meets one of its partner molecules — PD-L1 or PD-L2 — on another cell, the T cell is told to stand down.

The prescribing information summarizes the cancer side of this: binding of PD-L1 and PD-L2 to PD-1 “inhibits T-cell proliferation and cytokine production,” some tumors increase the amount of these partner molecules on their surface, and signalling through this pathway “can contribute to inhibition of active T-cell immune surveillance of tumors.” In plain words, some cancers survive by pressing the T cells’ off-switch.

Retifanlimab sits on the PD-1 receptor and blocks it from meeting PD-L1 and PD-L2. The label states that this “potentiates T-cell activity.” A 2025 crystal-structure study, which imaged the drug bound to PD-1 at a resolution of 1.54 ångström, found that the spot the antibody grips partly overlaps the place where the partner molecules normally attach, and that binding reshapes several flexible loops of the receptor.

The same mechanism explains the side effects. The label describes the drug class as “removing inhibition of the immune response with the potential for breaking of peripheral tolerance.” Peripheral tolerance is the set of brakes that keeps T cells from attacking the body’s own organs. When those brakes are released, T cells can turn on the lungs, bowel, liver, hormone glands, kidneys, skin or almost any other tissue. These immune-mediated adverse reactions are described in their own section below.

Both cancers in the approvals have features that drew researchers to this approach. Squamous cancer of the anal canal is usually driven by human papillomavirus: in the anal cancer trials on the label, tumor tissue tested positive for a papillomavirus marker in 75% and 93% of the samples that were reviewed. Most Merkel cell carcinomas carry a virus too. In 2008, researchers at the University of Pittsburgh identified a previously unknown polyomavirus in these tumors — now called Merkel cell polyomavirus — and found its DNA in 8 of 10 tumors, built into the tumor’s own genome in a clonal pattern in six of the eight. Virus-related cancers carry foreign proteins that T cells can recognize, which is one reason PD-1 blockade was tested in them. In the 2016 first-line trial of another PD-1 antibody, pembrolizumab, responses occurred in tumors with and without the virus (62% and 44%).

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Two US Approvals and Their Dates

The current US prescribing information, as published on DailyMed (September 2026 version), gives the drug’s initial US approval as 2023 and lists two cancers:

• Merkel cell carcinoma (first approval, 2023). For adults with Merkel cell carcinoma that has spread (metastatic) or has come back and grown locally (recurrent locally advanced). A 2023 drug-development review in the journal Drugs reported that this was an accelerated approval — the FDA pathway that allows approval on an early measure, here tumor shrinkage in a single-arm trial. The label marks the Merkel cell carcinoma indication as revised in December 2025, and the current text of the label no longer carries an accelerated-approval statement for it.
• Squamous cell carcinoma of the anal canal (May 15, 2025). The FDA approval summary, written by FDA reviewers, states that on May 15, 2025, the agency approved retifanlimab in two ways: together with carboplatin and paclitaxel as the first treatment for adults with anal canal squamous cancer that cannot be removed by surgery or has spread, and on its own for adults whose cancer has grown during or despite platinum chemotherapy, or who could not tolerate it. The label wording is “inoperable locally recurrent or metastatic” for the first use and “disease progression on or intolerance to platinum-based chemotherapy” for the second.

The label lists no contraindications, meaning no condition in which the label forbids its use outright. The warnings, rather than a contraindication list, carry the safety information.

The approvals rest on three trials, each described below: POD1UM-303/InterAACT 2 (a randomized trial with chemotherapy in anal cancer), POD1UM-202 (a single-arm trial of the drug alone in anal cancer after platinum chemotherapy) and POD1UM-201 (a single-arm trial in Merkel cell carcinoma).

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The POD1UM-303/InterAACT 2 Trial in Advanced Anal Cancer

The chemotherapy it was added to

Before this trial, the common first chemotherapy for anal cancer that had spread was settled by an earlier international trial, InterAACT, published in 2020. In 91 people who had not received chemotherapy for advanced disease, carboplatin plus paclitaxel was compared with the older cisplatin plus fluorouracil. Tumor shrinkage was similar (59% with carboplatin-paclitaxel and 57% with cisplatin-fluorouracil), but serious side effects occurred in 36% against 62%. Median progression-free survival was 8.1 against 5.7 months, and median overall survival 20 against 12.3 months. Carboplatin-paclitaxel then became the backbone that retifanlimab was tested on.

How the trial was run

POD1UM-303/InterAACT 2 was a double-blind, placebo-controlled phase 3 trial at 70 centres in 12 countries across the European Union, Australia, Japan, the United Kingdom and the United States. Between November 2020 and July 2023, 308 adults whose anal canal squamous cancer had come back and could not be operated on, or had spread, and who had not yet received chemotherapy for that advanced disease, were assigned at random to one of two groups of 154:

• retifanlimab 500 mg by vein every 4 weeks plus carboplatin-paclitaxel, or
• a placebo infusion plus the same carboplatin-paclitaxel.

Treatment lasted up to one year. People with human immunodeficiency virus could take part if the infection was well controlled (a CD4 count above 200 per microlitre and an undetectable viral load); 3.6% of those enrolled were living with it. Of the 308 people, 72% were women. People in the placebo group whose cancer grew could switch to retifanlimab alone, and the label reports that 77 of them (50%) did.

The main measure was progression-free survival: the time from joining the trial until the cancer was seen to grow on scans, or death from any cause, judged by reviewers who did not know which treatment each person received.

Progression-free survival

The 2025 primary report in The Lancet, the FDA approval summary and the label give the same figures:

• Median progression-free survival: 9.3 months (95% confidence interval 7.5 to 11.3) with retifanlimab plus chemotherapy, against 7.4 months (7.1 to 7.7) with placebo plus chemotherapy.
• Hazard ratio 0.63 (95% confidence interval 0.47 to 0.84; one-sided p = 0.0006). A hazard ratio of 0.63 means that, at any given time, the risk of the cancer growing or of death was about 37% lower in the retifanlimab group.
• The label adds that the cancer grew, or the person died, in 92 people (60%) in the retifanlimab group and 110 (71%) in the placebo group by the time of that analysis.

The difference in the medians is 1.9 months. The hazard ratio describes the whole follow-up period, not only the midpoint. The 2026 final report gave an updated progression-free survival hazard ratio of 0.62 (95% confidence interval 0.47 to 0.81).

Overall survival

At the interim analysis described in the FDA approval summary, median overall survival was 29.2 months with retifanlimab and 23 months with placebo, a difference that was not statistically significant (hazard ratio 0.70, 95% confidence interval 0.49 to 1.01). The 2026 final analysis in Annals of Oncology reported median overall survival of 32.8 against 22.2 months (hazard ratio 0.75, 95% confidence interval 0.55 to 1.01, p = 0.0305). The current label shows the same 32.8 and 22.2 months and states plainly: “OS results were not statistically significant.” The authors of the final report described the improvement as “consistent and clinically meaningful” and reported that an analysis adjusting for the people who switched from placebo to retifanlimab was consistent with the main result.

Tumor shrinkage and how long it lasted

The label gives an objective response rate — the share of people whose tumors shrank by a set amount — of 57% with retifanlimab against 45% with placebo. Complete disappearance of measurable tumor was seen in 38 people (25%) against 21 (14%). The median duration of response was 14.7 months against 7.2 months. The final report gave the response rates as 56.5% against 44.8%, and disease control (shrinkage or no growth) as 87.7% against 80.5%.

Side effects in the trial

Side effects were more common with the added antibody. In the 2025 report, serious adverse events occurred in 47.4% of the retifanlimab group against 38.8% of the placebo group, and grade 3 or worse events (severe or life-threatening) in 83.1% against 75.0%. The most common severe events were low neutrophil counts (35.1% against 29.6%) and anaemia (19.5% against 20.4%), both largely chemotherapy effects. Four deaths from adverse events occurred in the retifanlimab group, one of which (pancytopenia, a fall in all blood cell types) was judged treatment-related; one death occurred in the placebo group and was judged unrelated. The label reports that retifanlimab was permanently stopped because of a side effect in 11% of people in the combination group.

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Retifanlimab Alone After Platinum Chemotherapy

The second anal cancer approval rests on POD1UM-202, an open-label, single-arm phase 2 trial. It enrolled 94 adults whose anal canal squamous cancer had grown after platinum chemotherapy, or who could not take it. Each received retifanlimab 500 mg every 4 weeks; there was no comparison group.

• Tumors shrank in 13.8% (95% confidence interval 7.6% to 22.5%) — one complete response and 12 partial responses. The label rounds this to 14%.
• A further 35.1% had stable disease, for a disease control rate of 48.9%.
• Median duration of response was 9.5 months. The label reports that 65% of responders kept their response for at least 6 months and 41% for at least 12 months.
• Median progression-free survival was 2.3 months and median overall survival 10.1 months.
• The authors reported responses regardless of human immunodeficiency virus status, papillomavirus status, PD-L1 level or liver metastases. About 10% of the participants were living with human immunodeficiency virus.

In this trial, the label reports serious adverse reactions in 40% of people and permanent discontinuation because of a side effect in 4.3%. Because there was no comparison group, the trial cannot show whether the drug lengthened life; it shows how often tumors shrank.

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The Merkel Cell Carcinoma Results

Merkel cell carcinoma is a rare, fast-growing skin cancer that mostly affects older people and people with weakened immune systems. The disease, its virus and ultraviolet causes, and its other treatments are described on the Merkel Cell Carcinoma page.

The POD1UM-201 trial

The Merkel cell carcinoma approval rests on POD1UM-201, an open-label, single-arm phase 2 trial at 34 sites in the United States, Canada and Europe. It enrolled 101 adults with Merkel cell carcinoma that had spread or had come back locally and could not be treated with surgery or radiation, and who had not received any earlier drug treatment for advanced disease. Each received retifanlimab 500 mg by vein every 4 weeks for up to 2 years. The label reports a median age of 71; 76% were 65 or older and 39% were 75 or older. The Merkel cell polyomavirus was found in 76% of the biopsy samples that could be tested.

The 2025 full report, with a median follow-up for response of 22.2 months, gave these results:

• Objective response rate 54.5% (95% confidence interval 44.2% to 64.4%): 55 of 101 people. This included 18 complete responses (17.8%) and 37 partial responses (36.6%). The label gives the rate as 55%.
• Disease control rate 60.4%.
• Median duration of response was not reached among complete responders and was 25.3 months among partial responders. The label reports that 38 of the 55 responders (69%) kept their response for at least 12 months and 25 (46%) for at least 24 months.
• Estimated median progression-free survival was 16.0 months.
• Median overall survival was not reached; 63% of people were alive at 3 years.
• Grade 3 immune-related adverse events occurred in 11 people (10.9%).

In the label’s safety group for this trial (107 people), serious adverse reactions occurred in 26%, and retifanlimab was permanently stopped because of a side effect in 21%. The most common side effects (10% or more) were musculoskeletal pain (37%), fatigue (33%), itching (22%), diarrhoea (19%), rash (17%), fever (12%), nausea (12%) and constipation (11%).

How it compares with the other PD-1 and PD-L1 drugs

Avelumab (a PD-L1 antibody) and pembrolizumab (another PD-1 antibody) were studied in Merkel cell carcinoma before retifanlimab. The 2016 pembrolizumab trial treated 26 people with no earlier drug therapy and reported a response rate of 56% among 25 evaluable people. No trial has compared retifanlimab directly with either drug. A 2026 “matching-adjusted indirect comparison” — a statistical re-weighting of the POD1UM-201 patient data to resemble the population of a separate avelumab trial — reported a statistically significant difference in progression-free survival favouring retifanlimab (hazard ratio 0.590) and differences in overall survival (hazard ratio 0.800, confidence interval 0.492 to 1.303) and response that did not reach significance. After re-weighting, the retifanlimab group counted as about 42 patients, and the authors themselves wrote that the findings “are subject to residual confounding” and called for caution in reading them.

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How the Label Gives the Drug

The label gives retifanlimab as an infusion into a vein over 30 minutes, after dilution. It is not given as a rapid push. The label’s dosing table:

• Anal canal squamous cancer, first treatment with carboplatin and paclitaxel: 500 mg every 4 weeks, or 375 mg every 3 weeks, until the cancer grows, side effects become unacceptable, or for up to 12 months.
• Anal canal squamous cancer, alone after platinum chemotherapy: 500 mg every 4 weeks, or 375 mg every 3 weeks, for up to 24 months.
• Merkel cell carcinoma: 500 mg every 4 weeks, for up to 24 months.

The dose is a fixed amount, not calculated from body weight. The first-in-human trial, POD1UM-101, tested weight-based doses (1, 3 and 10 mg per kilogram) and then fixed doses of 375 mg every 3 weeks and 500 or 750 mg every 4 weeks; no dose-limiting toxicities occurred during dose escalation, and the authors identified 500 mg every 4 weeks and 375 mg every 3 weeks as the recommended doses. The label reports that blood levels rose in proportion to the dose between 375 and 750 mg, that steady levels were reached after about 3 months, and that the elimination half-life at steady state is 19 days. Age, sex, body weight, human immunodeficiency virus status, kidney function down to an estimated filtration rate of 26 and mild liver impairment had no meaningful effect on blood levels.

The label recommends no dose reductions. Instead, side effects are handled by pausing (“withholding”) the drug or stopping it permanently, depending on the organ involved and the severity, as laid out in the label’s Table 2. The label also states that liver enzymes, creatinine (a kidney marker) and thyroid function are checked at the start and periodically during treatment.

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Immune-Mediated Side Effects and Their Rates on the Label

The label’s first warning states that immune-mediated adverse reactions “may be severe or fatal” and “can occur in any organ system or tissue.” They can begin at any time after the drug is started, and can also appear after it has been stopped. More than one organ can be affected at once. The label lists the usual response as pausing or stopping the drug and giving corticosteroids (1 to 2 mg per kilogram per day of prednisone or an equivalent), tapered over at least a month once the reaction settles; hormone-gland problems are instead managed with hormone replacement.

Most of the rates below come from a pooled group of 452 people who received retifanlimab on its own in the trials. Where the label gives a separate figure for the combination with carboplatin-paclitaxel (154 people in POD1UM-303), it is shown too.

Lungs, bowel, liver and kidneys

• Pneumonitis (lung inflammation): 3.1% (14 of 452), including one fatal case (0.2%). Corticosteroids were needed in 10 of 14 people, and it resolved in 11 of 14. The label notes that, with other PD-1 and PD-L1 antibodies, pneumonitis is more common in people who have had radiation to the chest.
• Colitis (bowel inflammation): 2.7% (12 of 452) with retifanlimab alone, but 10% (16 of 154) with the chemotherapy combination. With the combination, corticosteroids were needed in 15 of 16 and it resolved in 15 of 16. The label notes that cytomegalovirus infection or reactivation has occurred in steroid-resistant colitis with this drug class.
• Hepatitis (liver inflammation): 3.5% (16 of 452), grade 3 or 4 in 2.6%. It resolved in 9 of 16.
• Nephritis with kidney dysfunction: 2% (9 of 452), grade 3 or 4 in 1.5%. It resolved in 4 of 9.

Hormone glands

• Hypothyroidism (an underactive thyroid): 10% (46 of 452); 78% of those affected received thyroid hormone. In the combination trial, hypothyroidism was reported in 14% against 3.3% with placebo.
• Hyperthyroidism (an overactive thyroid): 6% (26 of 452). The label notes that an underactive thyroid can follow an overactive phase.
• Thyroiditis: 0.7% (3 of 452), all grade 1.
• Adrenal insufficiency (the adrenal glands stop making enough cortisol): 0.9% (4 of 452) alone, but 5.8% (9 of 154) with the chemotherapy combination. It resolved in only 1 of 4 and 4 of 9 people respectively; all needed corticosteroids. A 2024 case report described a 73-year-old woman treated for endometrial cancer who developed loss of appetite, nausea, vomiting, weakness and salt imbalances six months after starting retifanlimab, with low cortisol and adrenocorticotropin levels; her symptoms settled after 3 days of intravenous hydrocortisone.
• Hypophysitis (inflammation of the pituitary gland, which can cause headache and visual changes): 0.7% (3 of 452). It resolved in 1 of 3.
• Type 1 diabetes, which can first appear as diabetic ketoacidosis: 0.2% (1 of 452). The person received insulin.

Several of these hormone problems did not resolve during follow-up, which in practice can mean lifelong hormone replacement.

Skin and rarer reactions

• Immune-mediated skin reactions: 10% (43 of 452), grade 3 or 4 in 1.3%. The label notes that severe blistering reactions — Stevens-Johnson syndrome, toxic epidermal necrolysis and drug rash with eosinophilia and systemic symptoms — have occurred with PD-1 and PD-L1 antibodies. One case of toxic epidermal necrolysis led to the drug being stopped in the Merkel cell carcinoma trial.
• Rarer reactions, seen in fewer than 1% of the 452 people or reported with other drugs of the class, include myocarditis (heart-muscle inflammation), pericarditis, vasculitis, pancreatitis, myositis, Guillain-Barré syndrome, myasthenia gravis, encephalitis, uveitis (which can threaten sight), haemolytic and aplastic anaemia, and rejection of a transplanted organ or corneal graft. The label also names a myocarditis-myositis-myasthenia gravis overlap syndrome.

The first-in-human trial gives a sense of the overall frequency in a broader group: immune-related adverse events occurred in 30% of people in the tumor-specific cohorts, most often thyroid problems, colitis and nephritis.

Signs the label lists for prompt contact

The label’s patient counselling section lists signs that patients are told to report to their care team immediately: new or worsening cough, chest pain or shortness of breath (pneumonitis); diarrhoea, blood or mucus in the stool, or severe abdominal pain (colitis); signs of hepatitis, of thyroid, adrenal or pituitary problems, or of diabetes; signs of kidney inflammation; and any new rash. Hospitals treat severe diarrhoea with blood, breathing difficulty and the signs of adrenal crisis as urgent.

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Infusion Reactions, Transplants, Pregnancy and Breastfeeding

• Infusion-related reactions. A severe (grade 3) infusion reaction occurred in 5 of 606 people (0.8%) who received retifanlimab. The label describes interrupting or slowing the infusion, or stopping the drug, depending on severity.
• Stem cell transplants from a donor. The label warns that fatal and other serious complications — including graft-versus-host disease and hepatic veno-occlusive disease — can occur in people who receive an allogeneic (donor) stem cell transplant before or after treatment with a PD-1 or PD-L1 antibody, even with other treatment in between.
• Pregnancy. The label states that the drug can cause harm to a developing baby, based on how it works. There are no data in pregnant women. In mice, blocking PD-L1 signalling disrupted the mother’s immune tolerance of the fetus and increased fetal loss. Antibodies of this type cross the placenta. The label tells prescribers to check pregnancy status before starting, and gives effective contraception during treatment and for 4 months after the last dose.
• Breastfeeding. No information exists on whether the drug passes into human milk. Because of the potential for serious reactions in a breastfed child, the label tells women not to breastfeed during treatment and for 4 months after the last dose.
• Infection. In mice lacking PD-1, tuberculosis infection was markedly more lethal, and blocking PD-1 worsened tuberculosis in monkeys, according to the label’s animal-study section.

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What Is Not Known

• Whether it lengthens life in anal cancer, by the trial’s formal test. Overall survival was longer in the retifanlimab group in both the interim and final analyses, but the label states that the overall survival results were not statistically significant. Half of the placebo group switched to retifanlimab after their cancer grew, which makes any survival difference harder to measure.
• How it compares with other checkpoint drugs. No trial has compared retifanlimab directly with pembrolizumab, avelumab, nivolumab or any other PD-1 or PD-L1 antibody, in either cancer. The indirect Merkel cell carcinoma comparison carries the authors’ own warning about confounding.
• Survival in Merkel cell carcinoma. The approval rests on tumor shrinkage in a single-arm trial of 101 people. There was no comparison group, so the trial cannot show how much longer people lived because of the drug.
• Who benefits most. In the anal cancer combination trial, 91% of tumors had PD-L1 on at least 1% of cells, so there is little information on tumors without it. People with active autoimmune disease, people needing immune-suppressing medicines and people with organ transplants were excluded from the trials.
• Small groups. Few people living with human immunodeficiency virus took part (3.6% in the combination trial), and the label notes that the single-agent trials did not include enough younger adults to tell whether they respond differently. Blood levels have not been studied in moderate or severe liver impairment, and the relationship between dose, blood level and effect “have not been fully characterized.” Safety and effectiveness in children have not been established.
• Long-term effects. No studies have assessed whether the drug can cause cancer or genetic damage. Several hormone-gland side effects had not resolved by the end of follow-up.
• Other cancers. Retifanlimab has been tested in other tumors. In the POD1UM-304 trial in advanced non-small-cell lung cancer, adding it to platinum chemotherapy gave a median overall survival of 18.1 against 13.4 months (hazard ratio 0.75), with more serious side effects (41% against 30%). Lung cancer is not among the uses on the current US label.

Decisions about cancer treatment belong with the treating oncology team, who weigh these trial results against each person’s own cancer and health.

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Key Research Papers

1. Rao S, Samalin-Scalzi E, Evesque L, Ben Abdelghani M, Morano F, Roy A, et al. Retifanlimab with carboplatin and paclitaxel for locally recurrent or metastatic squamous cell carcinoma of the anal canal (POD1UM-303/InterAACT-2): a global, phase 3 randomised controlled trial. Lancet. 2025;405(10495):2144-2152. PubMed PMID: 40517007
2. Rao S, Samalin-Scalzi E, Evesque L, Ben Abdelghani M, Morano F, Roy A, et al. Survival outcomes in POD1UM-303/InterAACT-2: a phase III study of retifanlimab plus carboplatin-paclitaxel in first-line advanced squamous anal cancer. Ann Oncol. 2026;37(8):1157-1166. PubMed PMID: 42097353
3. Gandhy SU, Casak SJ, Saung MT, Mishra-Kalyani PS, Tang S, Auth D, de Claro RA, Lemery SJ. FDA Approval Summary: Retifanlimab for the Treatment of Adult Patients with Metastatic or Inoperable Locally Recurrent Squamous Cell Carcinoma of the Anal Canal. Clin Cancer Res. 2026;32(20):4514-4518. PubMed PMID: 42555229
4. Rao S, Sclafani F, Eng C, Adams RA, Guren MG, Sebag-Montefiore D, et al. International Rare Cancers Initiative Multicenter Randomized Phase II Trial of Cisplatin and Fluorouracil Versus Carboplatin and Paclitaxel in Advanced Anal Cancer: InterAAct. J Clin Oncol. 2020;38(22):2510-2518. PubMed PMID: 32530769
5. Rao S, Anandappa G, Capdevila J, Dahan L, Evesque L, Kim S, et al. A phase II study of retifanlimab (INCMGA00012) in patients with squamous carcinoma of the anal canal who have progressed following platinum-based chemotherapy (POD1UM-202). ESMO Open. 2022;7(4):100529. PubMed PMID: 35816951
6. Grignani G, Rutkowski P, Lebbé C, Guida M, Gaudy-Marqueste C, Spagnolo F, et al. Phase II study of retifanlimab in patients with recurrent locally advanced or metastatic Merkel cell carcinoma (POD1UM-201). J Immunother Cancer. 2025;13(8):e012478. PubMed PMID: 40796223
7. Kang C. Retifanlimab: First Approval. Drugs. 2023;83(8):731-737. PubMed PMID: 37184754
8. Lakhani N, Cosman R, Banerji U, Rasco D, Tomaszewska-Kiecana M, Garralda E, et al. A first-in-human phase I study of the PD-1 inhibitor, retifanlimab (INCMGA00012), in patients with advanced solid tumors (POD1UM-101). ESMO Open. 2024;9(4):102254. PubMed PMID: 38387109
9. Cho SH, Park JM, Lee EH, Song YH, Jang YJ, Choi SB, Heo YS. High-resolution crystal structure of PD-1 in complex with retifanlimab, the FDA-approved immune checkpoint blocking antibody for treating Merkel cell carcinoma. Biochem Biophys Res Commun. 2025;742:151106. PubMed PMID: 39632294
10. Feng H, Shuda M, Chang Y, Moore PS. Clonal integration of a polyomavirus in human Merkel cell carcinoma. Science. 2008;319(5866):1096-100. PubMed PMID: 18202256
11. Nghiem PT, Bhatia S, Lipson EJ, Kudchadkar RR, Miller NJ, Annamalai L, et al. PD-1 Blockade with Pembrolizumab in Advanced Merkel-Cell Carcinoma. N Engl J Med. 2016;374(26):2542-52. PubMed PMID: 27093365
12. Porta C, Ghetti G, Povero M. Retifanlimab Versus Avelumab for the Treatment of Metastatic Merkel Cell Carcinoma: A Matching-Adjusted Indirect Comparison Analysis. Adv Ther. 2026. PubMed PMID: 42842181
13. Zhang W, Xiao L, Zhou G, Zhu H, Bi Y, Du J, Zhang D. Secondary adrenocortical insufficiency after treatment with retifanlimab: a case report. Front Immunol. 2024;15:1371527. PubMed PMID: 38915406
14. Lu S, Vynnychenko O, Kulyaba Y, Kuchava V, Ibrahim A, Moiseenko F, et al. Retifanlimab versus placebo in combination with platinum-based chemotherapy in patients with first-line non-squamous or squamous metastatic non-small-cell lung cancer (POD1UM-304): a phase 3, multiregional, placebo-controlled, double-blind, randomised study. Lancet Respir Med. 2025;13(12):1096-1107. PubMed PMID: 40983066
15. US National Library of Medicine, DailyMed. Retifanlimab-dlwr injection, for intravenous use — full prescribing information and Medication Guide (September 2026 version; indications revised 5/2025 and 12/2025, warnings revised 5/2026). DailyMed: retifanlimab

PubMed Topic Searches

1. PubMed: retifanlimab
2. PubMed: retifanlimab in anal canal cancer
3. PubMed: retifanlimab in Merkel cell carcinoma
4. PubMed: immune-related adverse events of PD-1 antibodies
5. PubMed: Merkel cell polyomavirus and immunotherapy

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Connections

• Drugs — the parent section for every drug page
• Anal Cancer — the disease behind the 2025 approval
• Merkel Cell Carcinoma — the disease behind the 2023 approval
• Human Papillomavirus (HPV) — the virus behind most anal canal cancers
• Skin Cancer — the wider family Merkel cell carcinoma belongs to
• Allison and Honjo — the checkpoint research that led to PD-1 antibodies
• Melanoma Immunotherapy: The Long-Term Trial Results — how other PD-1 antibodies performed over years
• Myocarditis — a rare immune side effect named on the label

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