Can Immunotherapy Cure Stage 4 Cancer?

Immunotherapy has produced long-lasting remissions in some people with stage 4 cancer, and a growing body of evidence suggests that a subset of those patients may genuinely be cured. The word “cure” remains contentious among oncologists when applied to metastatic disease, but ten-year follow-up data now show patients alive and disease-free long after stopping treatment, which is as close to proof as cancer medicine gets. The catch is that these outcomes are concentrated in certain cancer types and certain patients, and researchers are still working out why one person’s immune system eradicates widespread tumors while another’s barely slows them down.

What “Cure” Means When Cancer Has Spread

In oncology, “cure” usually means a person has no detectable cancer and the risk of it returning has dropped to nearly the same level as someone who never had cancer. For early-stage disease treated with surgery, that benchmark is relatively straightforward. For stage 4 cancer, where tumors have spread to distant organs, the conversation is different. Historically, the goal of treatment was to extend life and manage symptoms, not to eliminate the disease entirely. Immunotherapy has forced a revision of that framing, because some patients treated more than a decade ago remain in complete remission with no ongoing therapy.

One of the clearest signals comes from patients who achieved a complete response on checkpoint inhibitors and then stopped treatment. In a study of metastatic melanoma patients who discontinued pembrolizumab after their cancer disappeared entirely, about 91% remained disease-free two years later.¹ Similar patterns have been observed in advanced lung cancer: in a real-world study of patients who stopped checkpoint inhibitors after at least 18 months, those who had achieved a complete or partial response maintained a 12-month progression-free survival rate around 76%.² In metastatic Merkel cell carcinoma, patients who stopped immunotherapy in complete response had a progression rate of only 26% after a median follow-up of about a year.³

These numbers do not prove universal cure, but they show something genuinely new: a meaningful fraction of people with stage 4 cancer can stop treatment and stay cancer-free for years. Whether that constitutes a cure depends on how long you follow them and how strict your definition is. For many patients and their oncologists, it is functionally indistinguishable from one.

Melanoma Changed the Conversation

If any single cancer type demonstrates immunotherapy’s curative potential in stage 4 disease, it is advanced melanoma. Just over a decade ago, metastatic melanoma carried a median survival of roughly six to eight months.⁴ Since 2011, fourteen new agents have been approved, and the landscape has transformed.

The most striking data come from the CheckMate 067 trial, which followed patients with advanced melanoma for a minimum of ten years. In the group receiving the combination of nivolumab plus ipilimumab, median melanoma-specific survival exceeded 120 months, meaning more than half the patients had not died of their disease a full decade later. About 37% of combination-treated patients were still alive at study closeout. And among patients whose cancer had not progressed by the three-year mark, the ten-year melanoma-specific survival rate was 96% for the combination arm and 97% for nivolumab alone.⁵ That last number is remarkable: if you were still responding at three years, your chances of being alive from melanoma at ten years were essentially the same as the general population’s. Earlier readouts from the same trial, at a minimum of 6.5 years, showed median overall survival of about 72 months in the combination group.⁶

These are not cherry-picked best-case patients. The trial enrolled people with unresectable stage III or stage IV melanoma, a population that once had among the worst outcomes in oncology. The durability of these responses is what makes researchers willing to use the word “cure” in this setting, even if cautiously.

Which Other Stage 4 Cancers Respond

Melanoma’s success is not an isolated story, but the strength of the response varies widely by cancer type. A few patterns have become clear.

In advanced non-small cell lung cancer, checkpoint inhibitors have become a mainstay. A meta-analysis of randomized trials found that patients whose tumors expressed high levels of PD-L1, a protein that helps cancer hide from the immune system, had the strongest benefit. Those with PD-L1 expression of 50% or more showed a meaningful improvement in response rates compared with chemotherapy, while patients with very low expression saw little difference.⁷ Another meta-analysis confirmed that even patients with weaker PD-L1 expression still gained a survival advantage over chemotherapy, though it was smaller.⁸ In real-world practice, lung cancer patients with very high PD-L1 levels who received checkpoint inhibitors had a median survival of nearly four years, compared with about a year and a half for those with lower expression.⁹ Long-term cures in lung cancer remain less common than in melanoma, but a tail of long survivors is emerging.

Colorectal cancer tells a split story. Most advanced colorectal cancers respond poorly to immunotherapy. But about 5% of metastatic colorectal cancers have a feature called high microsatellite instability, which means their DNA repair machinery is broken and they accumulate many mutations. These tumors light up the immune system and respond impressively to checkpoint inhibitors, with deep and long-lasting responses reported.¹⁰ For the other 95%, immunotherapy alone has had limited impact.

Other cancers with notable immunotherapy responses include kidney cancer, bladder cancer, head and neck cancers, Hodgkin lymphoma, and certain types of gastric and esophageal cancer. But across all these tumor types, the fraction of patients who achieve durable complete responses remains a minority. The question that dominates the field right now is how to expand that minority.

Why Only Some Patients Respond

Predicting who will benefit from immunotherapy is one of the most active areas in oncology research. Several biological markers have emerged as useful, though none is perfect.

PD-L1 expression on tumor cells is the most widely used. As noted in the lung cancer data above, higher PD-L1 levels generally predict better responses. But PD-L1 testing is imperfect. Some patients with low expression still respond, and some with high expression do not. Tumor mutational burden, which measures how many mutations a tumor carries, is another predictor. Tumors with more mutations tend to produce more abnormal proteins that the immune system can recognize and attack.¹¹ Microsatellite instability status, as with colorectal cancer, is a related and sometimes overlapping indicator.

One of the more surprising findings in recent years is that the gut microbiome appears to influence immunotherapy outcomes. Patients who respond to checkpoint inhibitors have a different composition of gut bacteria compared with those who do not respond.¹² A meta-analysis in metastatic melanoma identified specific bacterial species, particularly Faecalibacterium, that were enriched in responders.¹³ The clinical significance is still being worked out, and no one is prescribing probiotic cocktails as cancer treatment yet, but this line of research has practical appeal because the microbiome is at least theoretically modifiable. Antibiotic use around the time of immunotherapy initiation has been linked to worse outcomes in some studies, which has prompted cautious recommendations to avoid unnecessary antibiotics when starting treatment.¹⁴

When Immunotherapy Fails

For many patients, immunotherapy either never works or stops working. Oncologists distinguish between primary resistance, where the cancer does not respond from the start, and secondary resistance, where the cancer initially shrinks but later returns. Both are common, and the mechanisms differ.

Primary resistance often involves tumors that have already walled themselves off from the immune system. The tumor microenvironment, the ecosystem of cells and signals surrounding a cancer, can be deeply suppressive. Certain immune cells within that environment actively shut down the T cells that immunotherapy is trying to unleash.¹⁵ Some tumors produce very few mutations, giving the immune system little to latch onto. Others lose the ability to display their internal contents to immune cells, essentially becoming invisible.

Secondary resistance is in some ways more frustrating, because it means the treatment was working. Cancer cells are genetically unstable, and under the pressure of a successful immune attack, surviving cells that happen to carry resistance-conferring mutations can expand and take over. The tumor may stop presenting the very antigens that T cells were targeting, or it may upregulate alternative immune-suppressive pathways to replace the one that was blocked.

Cellular Therapies and the Solid Tumor Challenge

Beyond checkpoint inhibitors, a second branch of immunotherapy uses living immune cells as the treatment itself. The two major approaches are CAR-T cell therapy and tumor-infiltrating lymphocyte (TIL) therapy.

CAR-T cells are engineered in a lab to recognize a specific target on cancer cells, then infused back into the patient. In blood cancers like certain leukemias and lymphomas, the results have been dramatic. Long-term follow-up data indicate that CAR-T cells can produce prolonged remissions and are probably curative for a subset of patients.¹⁶ In two patients with chronic lymphocytic leukemia who achieved complete remission in 2010, CAR-T cells were still detectable more than ten years later, and both patients remained in remission.¹⁷

Solid tumors are a harder nut to crack. CAR-T cell therapy has shown limited success against them, largely because solid tumors lack the clean, uniform surface targets that blood cancers present. The immunosuppressive microenvironment of solid tumors also hampers the engineered T cells once they arrive.¹⁸ Researchers are developing next-generation designs to overcome these barriers, but clinical results in solid tumors remain early-stage.¹⁹

TIL therapy takes a different approach. Instead of engineering new immune cells, it harvests T cells that have already infiltrated a patient’s tumor, grows them in large numbers, and reinfuses them. In February 2024, the FDA approved lifileucel, the first TIL product and the first cellular therapy approved for any solid tumor, for the treatment of advanced melanoma.²⁰ In a randomized trial, TIL therapy roughly doubled progression-free survival compared with ipilimumab, with 49% of TIL-treated patients showing an objective response versus 21% on ipilimumab.²¹ TIL therapy is resource-intensive, requiring specialized manufacturing for each patient, but it adds another option for cancers that have stopped responding to checkpoint inhibitors.

Combination Strategies That Push the Odds

Because immunotherapy alone works for only a fraction of patients, oncologists increasingly use it in combination with other treatments. The logic is to attack the tumor from multiple angles simultaneously, disrupting its defenses enough for the immune system to finish the job.

One well-studied combination pairs checkpoint inhibitors with radiation therapy. Radiation kills cancer cells directly, but it also releases tumor debris that can train the immune system to recognize the cancer. Occasionally, this produces the abscopal effect, where irradiating one tumor causes distant, unirradiated tumors to shrink as well. This phenomenon, long considered a curiosity, has become more common since the introduction of checkpoint inhibitors, which amplify the immune response that radiation initiates.^{22 23} The combination does not work reliably enough to be considered standard for all patients, but it has expanded the toolbox in settings where checkpoint inhibitors alone fall short.

Checkpoint inhibitors are also being paired with drugs that block the growth of blood vessels feeding tumors. By cutting off a tumor’s blood supply, these anti-angiogenic drugs can reshape the tumor microenvironment in ways that make it more accessible to immune cells. Immunotherapy plus chemotherapy combinations have become standard first-line treatment in several cancers, including lung cancer and some bladder cancers, on the basis that chemotherapy can debulk the tumor and release antigens while immunotherapy maintains the long-term immune surveillance.

Living With Long-Term Side Effects

The success of immunotherapy has created a new population of long-term cancer survivors who face a specific set of ongoing health issues. Checkpoint inhibitors work by releasing the brakes on the immune system, and an immune system without adequate brakes can attack healthy tissue. In the short term, these immune-related side effects can affect almost any organ: the thyroid, liver, lungs, skin, and colon are common targets. Most acute episodes are manageable with steroids or by pausing treatment.

But long-term survivors face something different. Some side effects persist or emerge months to years after treatment ends. Thyroid dysfunction, for example, is often permanent, requiring lifelong hormone replacement. Joint inflammation, dry mouth, and neurological effects like peripheral neuropathy can linger.²⁴ As one researcher put it, while some of these conditions can be easily treated, others, like brain-related effects, are not. The trade-off for most patients with stage 4 cancer is clearly worth it, but it is a trade-off that people entering treatment should understand.

The Financial Weight of Immunotherapy

Immunotherapy is expensive. A course of checkpoint inhibitor treatment can run into six figures, and for patients who remain on treatment for a year or two, the cumulative cost is substantial. Among cancer survivors on Medicare, high-cost immunotherapy was associated with a roughly 7-percentage-point increase in the likelihood of being unable to afford medical care.²⁵ In lung cancer patients specifically, the financial burden of immunotherapy has been linked to worse quality of life, not from the drug itself but from the stress of paying for it.²⁶ Cellular therapies like CAR-T and TIL treatment carry even higher price tags, sometimes exceeding several hundred thousand dollars per patient. Access remains uneven, shaped by insurance coverage, geography, and the availability of specialized treatment centers.

Personalized Cancer Vaccines on the Horizon

One of the most watched developments in immunotherapy is the emergence of personalized neoantigen vaccines, built from the unique mutations in an individual patient’s tumor. The idea is to train the immune system to recognize those mutations as foreign, mounting a targeted response that a checkpoint inhibitor alone might not trigger.

In melanoma, a personalized mRNA vaccine called mRNA-4157 (V940), when added to pembrolizumab as post-surgery adjuvant therapy, improved disease control compared with pembrolizumab alone in patients with high-risk disease.²⁷ Larger trials are ongoing. Perhaps even more striking, a phase 1 trial in pancreatic cancer, one of the most immunotherapy-resistant tumor types, tested a personalized mRNA vaccine combined with a checkpoint inhibitor and chemotherapy after surgery. At a median follow-up of about 3.2 years, patients who generated a T cell response to the vaccine had not yet reached median recurrence-free survival, while non-responders had a median of about 13 months. Vaccine-induced T cells remained detectable and functional years later.²⁸

These vaccine trials are still small and early, and they have so far been tested in the post-surgical setting rather than in patients with established stage 4 disease. But the principle matters: if you can teach the immune system to see a cancer’s unique fingerprint, you may be able to sustain immune surveillance for years, turning what would have been a death sentence into a chronic condition or even a cure. The field has been humbled before by technologies that looked promising in small trials and fizzled in larger ones, so cautious optimism is appropriate. But the trajectory, from Coley’s bacterial toxins in 1891 to ten-year melanoma survival data in 2025, points in one direction.²⁹