When Maureen Sideris was treated for colon cancer in 2008, her recovery followed the traditional and often physically demanding path of surgery and post-operative rehabilitation. The treatment was successful, but the process was long and exhausting.

Fourteen years later, when the 71-year-old New York resident was diagnosed with oesophageal cancer, her treatment took a markedly different form. Instead of surgery, chemotherapy or radiation, she enrolled in a clinical trial at Memorial Sloan Kettering Cancer Center and began receiving infusions of the immunotherapy drug Dostarlimab every three weeks.

Each session lasted about 45 minutes. After four months, her tumour had disappeared.Sideris says the result felt almost unreal. Apart from adrenal insufficiency that causes fatigue, she experienced few major side effects. “It’s unbelievable,” she said. “It’s almost like science fiction.”Her case reflects a broader shift underway in oncology, where immunotherapy a treatment strategy designed to help the body’s own immune system recognize and destroy cancer cells is increasingly moving from experimental promise to routine clinical application.

After decades of research, oncologists say immunotherapy is now producing long-term remission and, in some cases, functional cures for patients who previously faced invasive surgery or limited treatment options.“I get choked up and have goosebumps,” said Jennifer Wargo, a professor of surgical oncology and immunotherapy researcher at MD Anderson Cancer Center.

“People are living, and living with good quality lives. We’re talking about cures.”The science behind immunotherapy is based on a relatively simple principle. The immune system is naturally designed to identify and eliminate cells that appear foreign or abnormal, including cells that become cancerous.

Karen Knudsen, chief executive of the Parker Institute for Cancer Immunotherapy, said the body is normally able to detect and remove cells that look like they do not belong. But cancer can evade that surveillance by making itself appear indistinguishable from surrounding healthy tissue.

Immunotherapy aims to reverse that concealment by helping the immune system identify cancer for what it is and launch a targeted response.Two of the most established forms of immunotherapy today are CAR T-cell therapy and immune checkpoint inhibitors.CAR T-cell therapy involves removing T cells the immune cells responsible for targeting specific threats from a patient’s blood, modifying them in a laboratory so they can better detect cancer, and then returning them to the body.

These therapies are currently used primarily for blood cancers.Immune checkpoint inhibitors work differently. They disable one of the immune system’s built-in “off switches,” mechanisms that normally prevent excessive immune responses from damaging healthy tissue.

Some cancer cells exploit these off switches, effectively telling immune cells not to attack. Checkpoint inhibitors prevent that signal, allowing T cells to identify tumours as threats and respond accordingly.

The significance of this approach was recognized globally when the scientists behind checkpoint inhibitor research were awarded the Nobel Prize in Physiology or Medicine 2018. These drugs are now used across multiple cancer types.However, both approaches have limitations.

Researchers have struggled to make CAR T-cell therapies consistently effective against solid tumours, which account for more than 90% of new cancer diagnoses. The treatment is also expensive and logistically complex because it requires individualized cell engineering.Checkpoint inhibitors can be easier to administer, but they carry risks.

Samra Turajlic, a medical oncologist at the Francis Crick Institute, described the side effects as a “kaleidoscope,” reflecting how broadly the immune system can react once normal regulatory controls are reduced.

Because these drugs remove safeguards meant to prevent the body from attacking itself, patients may experience immune-related complications involving healthy organs as well as tumours.

According to the National Cancer Institute, common side effects include fatigue, diarrhoea and skin rashes, while rare complications can involve inflammation of the liver, kidneys and heart.

Even when side effects are manageable, the larger problem is inconsistency.Turajlic said no immunotherapy works for all patients. Response depends on multiple factors, including the structure of the tumour, how accessible it is to immune cells, and the biological characteristics of the patient’s own immune system.

Current estimates suggest only 20% to 40% of patients respond meaningfully to immunotherapy, meaning many undergo treatment, side effects and emotional strain without clear benefit.That gap has pushed researchers toward combination strategies and more personalized approaches.Wargo’s early research suggests patients who follow high-fibre diets may improve treatment response through changes in the gut microbiome, which can influence both immune behavior and tumour biology.

Other studies indicate that statins, commonly prescribed cholesterol-lowering drugs, may unexpectedly enhance immunotherapy by altering cellular communication pathways.Timing may also matter. Some recent findings suggest patients treated earlier in the day may respond better than those receiving therapy later, raising new questions about how biological rhythms influence cancer care.

Combining immunotherapy with radiation or ultrasound is another area of active research.Sandra Demaria of Weill Cornell Medical Center said radiation can make tumours more visible to the immune system by changing how cancer cells present themselves. Ultrasound therapy, which uses high-frequency sound waves to target tumours, may have similar effects.

For many researchers, however, the most important shift is not simply adding more treatments, but identifying which patients are most likely to benefit from specific therapies.“We can now move toward treating not the cancer, but actually the patient,” Demaria said.Knudsen said that approach is especially important because cancer is not a single disease.

Oncology encompasses hundreds of biologically distinct conditions, and even patients with the same diagnosis may have profoundly different disease behavior at the cellular level.That principle is already shaping clinical practice at Memorial Sloan Kettering.

Researchers there identified that tumours carrying a specific genetic signature respond especially well to checkpoint inhibitors such as dostarlimab. In small clinical trials conducted in 2022 and 2024, patients with rectal cancers carrying that profile saw complete tumour eradication.

The institution later expanded the study to 117 patients with different cancers including oesophageal, bladder and stomach tumours that shared the same genetic marker.

Among the 103 patients who completed the full course of treatment, 84 experienced complete disappearance of their tumours. Only two required additional surgery.

Sideris was among those patients.

Her case illustrates how immunotherapy is changing expectations around cancer treatment. What once required major surgery can, for a growing subset of patients, now be addressed through carefully targeted immune intervention.Researchers caution that such outcomes remain highly dependent on tumour biology and patient selection, and they do not apply universally.

But the progress has changed how many oncologists view the future of cancer care less focused on destroying tumours through increasingly aggressive intervention, and more centered on teaching the body to do the work itself.

India’s largest drugmaker by market value said it would pay $14 per share for Organon, representing a premium of more than 24% to Organon’s April 24 closing price, as it accelerates its strategy to deepen exposure to higher-margin specialty therapies including dermatology, oncology and obesity treatments.

The acquisition also strengthens Sun Pharma’s presence in women’s health and gives it entry into biosimilars, while broadening its reach into markets such as China, Brazil and other emerging economies where its footprint has been comparatively limited.

Sun Pharma shares closed 7% higher on Monday, adding 271.36 billion rupees ($2.88 billion) in market value, after rising as much as 9% earlier in the session. Organon shares rose 16% in premarket U.S. trading to $14.06.The deal includes Organon’s net debt of about $8.6 billion as of Dec. 31, 2025.

Sun said it would finance the transaction through a combination of existing cash reserves and committed bank financing.As of the same date, Sun Pharma’s debt stood at roughly $198.4 million, while annual profit was about $1.16 billion, giving it relatively strong balance sheet flexibility compared with the scale of the acquisition.

Analysts said the transaction would materially increase Sun’s earnings capacity and strengthen its long-term strategic positioning.Nuvama Institutional Equities analyst Shrikant Akolkar said the acquisition would effectively double Sun’s revenue and EBITDA by adding approximately $6.2 billion in sales with EBITDA margins of around 30%.

He said the transaction could be 30% to 40% earnings-per-share accretive by fiscal year 2028.“Funding is coming from a strong balance sheet, and debt concerns should ease by the third year,” Akolkar said, adding that the deal positions Sun to become a more dominant global pharmaceutical player by the end of the decade.

Organon’s portfolio includes more than 70 women’s health and general medicine products sold across around 140 countries, offering Sun a steady cash-generating business alongside its specialty drug pipeline.

The acquisition comes as Indian drugmakers with significant U.S. exposure face pressure from shifting U.S. tariff policies and pricing challenges in the generics market, prompting companies to seek stronger margins through branded specialty medicines and broader geographic diversification.

While analysts view the deal as strongly positive for earnings, some noted it may not dramatically alter Sun’s competitive standing in the U.S. market because Organon’s American business remains relatively modest.

Still, the transaction represents a major strategic step for Sun Pharma as it seeks to reduce dependence on traditional generic drug sales and strengthen its position as a global branded and specialty pharmaceuticals player.