ASCO 2026’s Quiet Lesson: Success with New Cancer Treatments Depends on Managing Side Effects

Today, the question “Which drug is more effective?” is no longer enough on its own. In some patient groups, the second question is becoming even more critical: Can this treatment be safely continued for this patient? As new treatments become more powerful, their side effect profiles also become more complex, more organ-specific, and more dependent on early intervention.

This is precisely where ASCO 2026’s quiet message lies: the future winners in cancer treatment will not simply be centers with access to new drugs. The real difference will be made by centers that detect side effects early, triage patients correctly, rapidly involve the necessary specialists, and sustain treatment without compromising quality of life.

The ADC era: responses increase, toxicity profiles change

One of the most striking themes at ASCO 2026 was the rapid movement of antibody-drug conjugates into earlier lines of treatment and combination therapies. ADCs can be described simply as “smart drugs that carry chemotherapy to a target,” but this definition is incomplete in clinical practice. ADCs are not merely targeted delivery systems; they are also complex treatments carrying powerful cytotoxic payloads with distinctive side effect profiles.

For example, in PD-L1-positive advanced lung cancer, the combination of Sac-TMT + pembrolizumab provided a strong PFS advantage over pembrolizumab alone; an approximately 65% reduction in the risk of progression or death was reported. However, in the same study, grade 3 or higher treatment-related adverse events were substantially more frequent in the combination arm; toxicities such as neutropenia, anemia, and stomatitis stood out.

Similarly, in metastatic urothelial cancer, enfortumab vedotin + pembrolizumab has become one of the strongest practice-changing examples of ADC + immunotherapy, with its long-term survival and complete response rates. However, side effects such as peripheral neuropathy, skin reactions, hyperglycemia, diarrhea, and pneumonitis / ILD require close management of this combination.

Pneumonitis / ILD: a quiet but critical side effect of the new era

One toxicity requiring particular attention in the era of new drugs is interstitial lung disease / pneumonitis. This condition can sometimes begin with a mild cough, shortness of breath on exertion, or unexplained fatigue. If recognized late, it may lead to a need for oxygen, hospitalization, and life-threatening respiratory failure.

This risk is especially pronounced with certain ADC platforms. The safety information for trastuzumab deruxtecan identifies ILD / pneumonitis as an important toxicity requiring a specific warning; when symptomatic ILD / pneumonitis develops, permanent discontinuation of the drug and prompt initiation of corticosteroid treatment are recommended.

The main lesson here is this: managing side effects of new-generation treatments involves more than monitoring blood counts. Simply telling a patient “come in if you develop a fever” is no longer enough. Cough, shortness of breath, fatigue, diarrhea, mouth sores, skin rash, neuropathy, vision changes, headache, confusion, and signs of infection must be monitored as part of successful treatment.

Targeted therapies are not “easy tablets” either

Side effect management is not limited to ADCs. Patients and physicians sometimes perceive oral targeted treatments as “milder” therapies or treatments “unlike chemotherapy.” Yet these drugs can also cause serious, unexpected side effects that sometimes require rapid intervention.

In RET fusion-positive lung cancer, the AcceleRET-Lung study showed that first-line pralsetinib prolonged PFS compared with standard treatment; median PFS was 18,7 months versus 9,0 months, and the objective response rate was 65,5% versus 41,6% . However, the infection signal was striking: infections occurred in %72of the pralsetinib arm versus %52 of the standard treatment arm; the fatal infection rate in the pralsetinib arm was reported as %7 . ILD / pneumonitis risk is also among the safety issues for pralsetinib.

This example does not diminish the clinical value of new targeted agents; on the contrary, it shows that centers must be far more systematic about infections, lung toxicity, liver dysfunction, and hematological side effects to realize these agents’ full potential.

As efficacy increases, side effects above grade 3 also increase

Efficacy data from many studies at ASCO 2026 were very strong, but rates of grade 3 or higher toxicity showed that clinical practice needs to be prepared. This does not mean “new treatments are toxic and should not be used.” The more accurate message is: As treatments become more powerful, their toxicity profiles become more diverse and their management more specialized.

In platinum-resistant ovarian cancer, the ROSELLA study showed a significant overall survival advantage with relacorilant + nab-paclitaxel; median OS was 16,0 months versus 11,9 months, with a 35% reduction in the risk of death reported. However, high-grade adverse events and serious adverse events were more frequent in the combination arm.

High-grade treatment-related adverse events also represent an important clinical issue with new immunotherapy and antiangiogenic combinations in nonsquamous lung cancer, such as benmelstobart + chemotherapy followed by anlotinib maintenance. This shows that new combinations need to be assessed not only for PFS or OS, but also for their feasibility in real-world practice, patient monitoring, emergency presentations, and supportive care requirements.

Safety observed in clinical trials may differ in real-world practice

Much of the data we see at ASCO is obtained under clinical trial conditions. This distinction is crucial. In clinical trials, patients are usually monitored much more closely. Research nurses, coordinators, regular protocol-mandated assessments, laboratory monitoring, and rapid intervention algorithms create a strong safety net around the patient.

In many clinical trials, patients receive a rapid response when they report a side effect; when toxicity develops, treatment interruptions, dose reductions, additional investigations, supportive care, or hospitalization are clearly defined in the protocol. In routine practice, however, the same patient may struggle to obtain an appointment, be assessed correctly in the emergency department, secure admission, or obtain reimbursement or access to medication.

Therefore, a treatment delivered safely in a clinical trial may be harder to manage when it moves into routine practice without the same support system. This is why it is no coincidence that centers with clinical trial experience recognize side effects earlier, intervene at the right time, and can safely sustain treatment.

Patient-reported outcomes are no longer “additional data”; they represent the real value of treatment

Some studies collect patient-reported outcomes regularly. Patients systematically report their pain, fatigue, diarrhea, shortness of breath, sleep quality, daily functioning, and treatment-related burden. This makes it possible to capture a side effect as the patient’s actual lived experience, beyond the laboratory result observed by the clinician.

For example, patient-reported quality of life analyses of niraparib maintenance in the PRIMA/ENGOT study demonstrated the importance of measuring patients’ treatment experience alongside clinical efficacy during maintenance treatment. The goal of maintenance therapy is not simply to delay recurrence; it is to preserve patients’ quality of life as much as possible after chemotherapy.

Future phase 3 studies need to incorporate not only PFS, OS, and response rates, but also patient-reported outcomes, dose reductions, treatment discontinuations, emergency presentations, hospital admissions, financial toxicity, and long-term quality of life more comprehensively. A clinician may record a side effect as “grade 2,” while the patient experiences the same side effect as a major burden disrupting daily life.

The greatest gap in routine practice: the support system

Drug access alone will not be what makes the real difference in the oncology practice of the future. Access to drugs is very important, but the success of new drugs will be determined by the quality of the system managing them. In routine practice, patients do not always have a research team available 24 hours a day. Not every center may have an experienced oncology nurse, toxicity algorithms, rapid side effect triage, PRO monitoring, an emergency presentation protocol, or a multidisciplinary side effect management team.

In the era of new treatments, however, these supports should become a safety standard, rather than a luxury. Pneumonitis must be recognized early in a patient receiving an ADC. Colitis, hepatitis, endocrinopathy, and pneumonitis must be identified in a patient receiving immunotherapy. Diarrhea, infection, hypertension, liver toxicity, and organ-specific side effects must be monitored in a patient receiving targeted therapy. Hypertension, proteinuria, bleeding, and thrombosis risk must be managed in a patient receiving antiangiogenic therapy.

The new quality standard: centers that detect toxicity early

Successful oncology centers of the future will do more than know the latest drugs. They will detect side effects early and keep patients safely on treatment. At these centers, trained oncology nursing, a patient support line available 24 hours a day, standardized toxicity algorithms, and integrated work with the emergency department should become a natural part of treatment.

In addition, teams in pulmonology, dermatology, gastroenterology, endocrinology, cardiology, infectious diseases, nutrition, psychiatry/psychology, and palliative care should become active participants in modern oncology practice, beyond consultants called in only when needed.

The message for Türkiye: safe delivery infrastructure should be a goal alongside access to new drugs

Türkiye has made significant progress in clinical research. Many of our centers participate in international studies, and many scientists from our country play active roles in global oncology research. This is extremely valuable, because clinical research not only generates science but also gives our patients early access to new drugs under ethical, controlled conditions.

However, Türkiye’s goal in the coming period should extend beyond access to more new drugs. The infrastructure for delivering these drugs safely must also be strengthened. Side effect management boards will become as important as molecular tumor boards, comprehensive toxicity triage systems as important as comprehensive NGS, and the quality of centers that can safely sustain treatment as important as access to new drugs.

Access to new drugs is an achievement, but safely sustaining their use is an even greater one. Even the most effective drug loses some of its real value when a patient must stop treatment early, has a side effect recognized late, is not assessed correctly in the emergency department, or experiences a severe deterioration in quality of life.

ASCO 2026’s quiet but powerful message

The visible face of ASCO 2026 consisted of new drugs, powerful combinations, impressive survival curves, and striking response rates. Its quieter, deeper message was: The new era of cancer treatment is not only an era of more effective drugs; it is an era of safe, sustainable, patient-centered delivery.

Today, we must add a second question alongside “Does this drug work?”: Can we safely continue this treatment for this patient? True success in cancer means more than shrinking a tumor. It means keeping patients safely on treatment, preserving their quality of life, and maintaining their strength for as long as possible.

Conclusion

ASCO 2026 showed us that cancer treatment is becoming more powerful at great speed. It also reminded us that stronger treatments require stronger clinical systems. ADCs, immunotherapy combinations, targeted agents, and cellular therapies can reach their true value only with appropriate patient selection, early diagnosis of toxicity, patient education, multidisciplinary support, and systematic real-world monitoring.

In the coming period, oncology centers will be assessed not only by their access to new drugs, but also by how safely, sustainably, and with what focus on patients they deliver them. True success in cancer treatment now means more than shrinking tumors; it means keeping patients on treatment with their strength, safety, and quality of life preserved.