Immunotherapy's "Sting in the Tail": Life-Threatening Toxicity Persists Long After Cancer Is Cured
核心洞察
Immunotherapy has transformed outcomes for once-nearly-untreatable cancers, with advanced melanoma ten-year survival rising from under 5% to over half of patients.
A patient with triple negative breast cancer (搜索) developed colitis (搜索), pneumonitis (搜索), and inflammatory arthritis (搜索) after just three doses of pembrolizumab, with side effects persisting 17 months after her last dose.
The largest European study of 545 patients across 34 UK hospitals found two-thirds suffered immune-related side effects, nearly half required unplanned hospital stays, and four patients died.
A patient treated for triple negative breast cancer (搜索) (TNBC) received what her surgeon called "the best possible result" — a clear pathology report confirming all cancer cells had been killed. Yet 17 months after her last dose of immunotherapy, she remains in a daily battle with the treatment's side effects, a phenomenon researchers now recognize as far from rare.
The patient, a 56-year-old who ran three times a week and had been a vegetarian since her teens, discovered a lump in her right armpit in November 2024 during a routine breast self-check. A month later, scans and a biopsy confirmed triple negative breast cancer (搜索) — a rarer, more aggressive form that is harder to treat because it lacks the receptors targeted by many of the most effective drugs.
Her treatment plan included six months of chemotherapy alongside pembrolizumab, an immunotherapy drug approved by the NHS just two years before her diagnosis. Pembrolizumab belongs to a new generation of treatments that work by "taking the brakes off the immune system," allowing it to recognize and attack cancer cells that would otherwise evade detection.
The Promise of Immunotherapy
Immunotherapy has, with good reason, been hailed as revolutionary. Introduced less than two decades ago, it has transformed the outlook for cancers once considered almost impossible to treat.
The most dramatic example is advanced melanoma, the deadliest form of skin cancer. Until little more than a decade ago, fewer than 5 per cent of patients were alive ten years after their diagnosis. Today, thanks to immunotherapy, more than half survive that long, and some are considered cured — an astonishing turnaround that many cancer specialists once thought impossible.
Similar breakthroughs have followed in some forms of lung and kidney cancer. Researchers are also seeing encouraging results in pancreatic cancer and other notoriously difficult tumours, raising hopes that immunotherapy's success story is only just beginning.
The Cost of a Super-Charged Immune System
But the treatment can come at a significant cost. Patients often develop side effects caused by their immune system attacking healthy tissue, and some are left with health problems that persist long after treatment has ended.
"By revving up the immune system to attack cancer, immunotherapy can also cause it to attack healthy parts of the body," the patient wrote. "But what I hadn't fully grasped was that unlike chemo, where side effects are unpleasant but usually short-lived, immunotherapy toxicity can flare up years after treatment."
The patient's oncologist was candid about the risks, warning that the drug could cause the immune system to attack her thyroid, lungs, liver, bowel, skin, or heart. She chose to proceed, reasoning that "knowing the poor prognosis women with TNBC face, I wanted to throw everything at the tumour."
In early March, everything changed. She developed acute diarrhoea up to 14 times a day, and her consultant diagnosed colitis (搜索) — inflammation of the large intestine. Her immune system was attacking her digestive system. Because colitis can be life-threatening, she spent every day in the emergency department receiving high-dose steroid infusions.
The cancer treatment had to stop completely while the oncology team worked to calm her immune system. She was forced to stop pembrolizumab after just three doses instead of the planned 17.
A Cascade of Complications
The complications did not end with colitis (搜索). By June, she could no longer climb the stairs without stopping to catch her breath and developed a relentless dry cough. After a blood transfusion, her temperature soared and she struggled to breathe, requiring an ambulance ride to A&E.
Antibiotics made no difference. Her chest felt "as though it were being crushed in a metal vice." The most likely culprit was pneumonitis (搜索) — her super-charged immune system was now attacking her lungs. After 48 hours, a specialist toxicity team started her on large doses of IV steroids, and within hours her breathing improved.
Her surgery was delayed while her lungs recovered, but by the end of July she received the best news of her life: there was no sign of cancer. "It's impossible to know which of the five medications killed off my tumour but I toasted the team, the chemo and the pembrolizumab that night."
Yet her immune system had not finished with her. As soon as she came off steroids, her colitis (搜索) returned. She also developed severe joint pains, initially attributed to steroids weakening her muscles. By January, she felt "96, not 56," as the pains spread to her hips, knees, wrists, elbows, and heels. When she restarted steroids, the pain improved overnight, confirming a diagnosis of inflammatory arthritis (搜索).
The Scale of the Problem
The patient initially assumed she was simply unlucky. But the largest study in Europe, which followed 545 patients receiving the same treatment across 34 UK hospitals, found that two-thirds suffered an immune-related side effect, nearly half needed unplanned stays in hospital, and four patients died — including three whose lungs were attacked by pneumonitis (搜索).
Professor Anna Olsson-Brown, chief executive of the Immuno-Oncology Clinical Network (搜索) (IOCN) and chair of the UK Society for Medical Oncology, leads the team that treated the patient. She explains the scope of the challenge.
"Severe or life-threatening toxicity affects somewhere between one in five and one in two patients, depending on the treatment, with many left with long-term, life-altering, symptoms," Professor Olsson-Brown said. "With 25,000 patients treated with immunotherapies last year in England alone, these toxicities are not a rare complication. They are a routine part of the treatment."
Professor Richard Simcock, chief medical officer at Macmillan Cancer Support (搜索), highlighted the uncertainty patients face. "One of the hardest aspects of immunotherapy toxicity is its unpredictability. We don't yet have a way of understanding who will be affected, what side effects they may get and, crucially, how long problems may last. All of this massively contributes to the uncertainty."
The Broader Burden
The effects extend beyond individual patients. The list price of a full course of pembrolizumab is nearly £90,000, though the NHS receives a discount. Emergency admissions, specialist drugs, and years of follow-up add to the burden on struggling cancer units.
The patient was fortunate to have access to a specialist immunotherapy toxicity team in Sussex, but she notes that such services "are few and far between." She also observed that non-specialist medics do not always understand immunotherapy side effects, underscoring the need for patients to advocate for themselves.
Despite the ordeal, she does not regret her decision. "During sleepless nights, when the cocktail of pills or joint pains keep me awake, I relive those terrifying times in A&E. Did I make the wrong decision in agreeing to immunotherapy? Deep down, I know I'd still say yes. It's very likely it helped get rid of my cancer, just as it has for tens of thousands of people. I just hope that medics also discover new ways to treat the sting in the tail."