The review, published in Supportive Care in Cancer by Mellar P. Davis and Boris Kiselev of Atrium Health in Charlotte, North Carolina, synthesizes evidence from meta-analyses, meta-regressions, and methodological studies across multiple therapeutic domains. Its central claim is provocative: placebo-response inflation should be treated as a determinant of what trial designers call assay sensitivity — a trial’s ability to distinguish a true treatment effect from nonspecific improvement — rather than as an unavoidable background hum of symptom variability. In symptom-focused oncology trials, where the primary outcomes are patient-reported and the symptoms themselves fluctuate, the stakes of getting this right are unusually high.

The mechanisms behind placebo-response inflation fall into several distinct categories. The first are operational: the sheer structure of modern trials. Evidence from meta-regressions in psychiatry shows that the number of study sites and the density of recruitment at each site influence how much patients improve on placebo. Large, rapidly recruiting multicenter trials tend to dilute the apparent treatment effect, a pattern documented in antidepressant trials over three decades and in studies of antipsychotics, where meta-regression analyses have questioned whether drug and placebo responses remain connected as sample sizes grow. A 2026 meta-analysis of adjunctive trials for negative symptoms in schizophrenia found that effect sizes deflate as sample size increases, a signature of placebo-arm inflation rather than weakening drugs.

Psychological mechanisms form the second category, and they are the most intuitively powerful. Expectancy — what a patient believes a treatment will do — directly shapes symptom reporting, particularly for subjective outcomes like pain and fatigue. Blinding integrity compounds the problem. When patients or clinicians can guess who is receiving the active drug, often because of recognizable side effects, expectancy effects contaminate both arms of the trial. This has been a particular embarrassment in cannabis-based medicine research: a systematic review of trials of cannabis-based therapies for pain found that placebo responses tracked media attention, and commentators have described inadequate blinding as the Achilles heel of medical cannabis studies. In oncology, where hope is a clinical reality, expectancy effects may be especially potent.

Statistical mechanisms provide the third pillar. Regression to the mean — the tendency of extreme values to move toward the average on repeated measurement — guarantees that patients enrolled at their symptomatic worst will often improve regardless of treatment. This is why entry criteria that demand high baseline symptom severity, combined with a single baseline assessment, virtually manufacture placebo improvement. The review notes that symptom variability and chronicity act as disease-related moderators of this process: fluctuating symptoms measured at an unstable moment produce apparent treatment responses that are pure statistical artifacts. Repeated baseline assessments before randomization are one straightforward way to separate real change from regression to the mean.

The oncology-specific evidence is sobering. Studies of fatigue in patients with advanced cancer have documented clinically meaningful improvement in placebo arms of double-blind trials, and recent work comparing blinded and open-label cancer fatigue trials shows that placebo effects are substantial even under rigorous conditions. An exploratory analysis of the ABCD randomized clinical trial has even begun hunting for predictive biomarkers of placebo response in patients with cancer, suggesting that who improves on placebo may eventually be identifiable in advance. Earlier foundational work on placebo effects in oncology, dating back two decades, had already flagged the issue; the new review argues that the field has not adequately acted on it.

What makes supportive oncology and palliative care uniquely vulnerable is the convergence of all these mechanisms in a single research setting. The endpoints are subjective and patient-reported. The symptoms — pain, fatigue, nausea, dyspnea — are inherently variable and often worsening with disease trajectory. Recruitment is typically multicenter and spread across sites of uneven quality. The interventions themselves, whether drugs, behavioral programs, or procedural techniques, are expectancy-sensitive by nature. And the patient population faces progressive illness, which introduces disease-related moderators that other fields rarely confront. A trial that stacks all of these risk factors is structurally primed to produce a large placebo response and a correspondingly weak signal of therapeutic benefit.

The methodological implications are concrete. The review points to several design levers with empirical support. Controlling recruitment density and site quality can reduce operational inflation. Psychoeducational procedures that recalibrate participant expectations have been shown in all-placebo psychiatric studies to mitigate placebo response, offering a template for oncology trials. Placebo run-in periods, in which potential responders to placebo are identified before randomization, have been associated with reduced placebo response in antidepressant trials, though they raise their own ethical and interpretive questions. Active placebos — control agents that mimic the side effects of the real drug — can protect blinding integrity but are rarely used. Balanced placebo designs, which cross pharmacological status with expectancy instructions, have demonstrated that conventional double-blind trials may actually underestimate true drug effects by entangling them with expectation.

None of these fixes is free of trade-offs. Placebo run-ins select a population that may not represent clinical practice. Active placebos can introduce their own symptoms that confound reporting. Expectancy manipulation raises questions about informed consent. And in palliative care, where trial windows are short and populations are fragile, adding repeated baseline assessments or complex designs imposes real burdens on patients and sites. The review’s contribution is to frame these not as isolated tactical choices but as a coherent, mechanism-based strategy: trialists should diagnose which mechanisms are most likely to inflate placebo response in their specific setting and design against them deliberately, rather than discovering the problem in a failed readout.

The broader lesson extends beyond oncology. The same inflation dynamics have eroded effect sizes in psychiatry, where decades of meta-regression work have mapped the relationship between trial characteristics and placebo response, and in pain research, where blinding failures have repeatedly muddied the evidence base for cannabinoids. Supportive oncology, the authors argue, should learn from these fields before its own evidence base accumulates the same distortions. If placebo-response inflation is a design-sensitive and measurable quantity, then every inflated placebo arm is not just a failed trial but a data point about how trials should be built. Treating it that way could mean the difference between abandoning an effective symptom therapy and proving that it works.

Subject of Research: Mechanisms of placebo-response inflation in symptom-focused clinical trials in supportive oncology and palliative care

Article Title: Placebo-response inflation in supportive oncology symptom trials: mechanisms, methodological challenges, and design implications

Article References: Davis, M. P., & Kiselev, B. (2026). Placebo-response inflation in supportive oncology symptom trials: mechanisms, methodological challenges, and design implications. Supportive Care in Cancer, 34(10), Article 962. https://doi.org/10.1007/s00520-026-11218-4

Image Credits: AI Generated

DOI: 10.1007/s00520-026-11218-4

Keywords: placebo response, supportive oncology, palliative care, clinical trials, symptom management, regression to the mean, expectancy, assay sensitivity, blinding integrity, patient-reported outcomes, cancer fatigue, trial design

The trial, known as FASTEX, was conducted by researchers at the Exercise Medicine Research Institute at Edith Cowan University in Perth, Australia, working with clinicians at Sir Charles Gairdner Hospital, Fiona Stanley Hospital and Joondalup Health Campus. Women with histologically confirmed breast cancer who were scheduled to receive neoadjuvant or adjuvant chemotherapy, with or without immunotherapy, were invited to take part. Rather than being randomly assigned, participants chose their own intervention: thirteen women opted for the supervised exercise programme, five chose a fasting-mimicking diet arm reported separately, and because no eligible participants volunteered for usual care, a convenience control group of six women was recruited to provide blood samples for biomarker comparison.

The exercise prescription was deliberately pragmatic. Sessions lasted roughly sixty minutes and combined a warm-up, fifteen to twenty minutes of aerobic work on a treadmill or stationary bike, twenty to twenty-five minutes of resistance training targeting the major upper- and lower-body muscle groups, and a cool-down. Participants were asked to attend two supervised sessions during chemotherapy weeks and three during non-treatment weeks, with intensity individually tailored to maintain a target rating of perceived exertion between twelve and sixteen on the Borg six-to-twenty scale. Loads and volumes were progressively increased, and by the end of the twelve weeks the average resistance training load had risen by ten to sixty per cent, with total training volume approximately doubling.

Feasibility was the study’s primary outcome, and the results were encouraging. Retention reached 84.6 per cent, with eleven of thirteen participants completing the programme; the two withdrawals were both related to travel rather than to the exercise itself. Attendance averaged 83.6 per cent and adherence to the prescribed sessions 77.9 per cent, both exceeding the pre-defined thresholds of 75 per cent. Most missed sessions were attributable to treatment-related side effects such as fatigue, gastrointestinal symptoms and pain, while session modifications were typically driven by medical considerations such as the presence of a PICC line or by comorbidities. Only one adverse event, a transient episode of mild hypotension in a participant with pre-existing hypertension, was recorded across the entire intervention.

The immunological findings formed the scientific core of the study. Using spectral flow cytometry on cryopreserved peripheral blood mononuclear cells, the researchers characterised T cell and natural killer cell subsets in fine detail, tracking differentiation, activation, senescence and exhaustion markers. Compared with controls, the exercising women showed a significantly greater increase in CD8-positive effector memory cells re-expressing CD45RA, known as EMRA cells, with a large effect size, alongside a significant reduction in CD8-positive naïve T cells. Signals toward significance were also observed for central memory CD8 cells, for CD8 cells expressing CD57, and for CD8 cells expressing PD-1, each of which shifted more in the exercise group than in the controls.

Interpreting these shifts requires care, and the authors were explicit about the alternatives. An expansion of EMRA and CD57-positive CD8 T cells could, in principle, indicate immunosenescence, the accumulation of terminally differentiated cells with limited proliferative capacity. However, EMRA cells commonly express high levels of cytotoxic machinery and can execute immediate effector functions, and PD-1, although classically an exhaustion marker, is also transiently upregulated during T cell activation. Because no changes were seen in other exhaustion markers such as CTLA-4 and TIM-3, the researchers suggest the pattern may instead reflect a functional shift toward a low-proliferative but highly cytotoxic effector state, consistent with preclinical work showing that muscle-derived metabolites such as lactate can promote cytotoxic differentiation of CD8 T cells.

Metabolic data added a second layer of interest. The control group showed a significant rise in fasting insulin over the study period while the exercise group did not, a between-group difference that reached statistical significance. Because glucose levels did not change in parallel, the authors interpret the insulin rise in controls as consistent with compensatory hyperinsulinaemia driven by emerging peripheral insulin resistance, a well-recognised consequence of chemotherapy that is linked to adiposity, inflammation, hormonal alteration and loss of muscle. Exercise, by enhancing skeletal muscle insulin sensitivity and GLUT4-mediated glucose uptake, may have blunted this trajectory, although the authors caution that the control group’s samples were not collected in a fasting state, a logistical constraint that limits firm conclusions.

Body composition and patient-reported outcomes rounded out the picture. Despite ongoing chemotherapy, the exercising women maintained stable body weight, fat mass and lean mass, with signals toward modest gains in lean mass of roughly 0.8 kilograms. This stability matters clinically, because chemotherapy typically drives fat gain and lean tissue loss, and higher adiposity after diagnosis predicts poorer breast cancer-specific and overall survival. On the questionnaire side, global quality of life measured by the EORTC QLQ-C30 improved significantly, rising by 16.7 points, with smaller improvements across physical, emotional and social functioning domains, and fatigue showed a signal toward improvement on the FACIT-F Trial Outcome Index. Participants rated the burden of the programme as very low and reported perceived benefits for well-being and treatment tolerance.

Seven participants received neoadjuvant chemotherapy, allowing a preliminary look at pathological complete response, the disappearance of invasive cancer in the resected specimen. Three of four exercising patients and all three controls achieved a complete response, a uniformly high rate that precludes any conclusion about whether exercise influenced treatment efficacy, particularly since the one non-responder had inflammatory breast cancer, a subtype associated with lower response rates. The authors stress that future studies should directly test whether exercise-induced immune modulation translates into improved therapeutic response.

The limitations of the pilot are substantial and the authors acknowledge them candidly. Participants self-selected into the exercise arm, raising the possibility that the programme appealed mainly to motivated women with the transport, time and physical capacity to attend supervised sessions, so feasibility in the broader population may be lower. The sample was small, the control group was a convenience sample of unequal size, menopausal status differed between groups at baseline, and chemotherapy regimens and blood sampling intervals varied. No functional immune assays or tumour infiltration analyses were performed, so it remains unknown whether the observed phenotypic changes alter immune cell behaviour in practice. Even so, the study’s comprehensive immune phenotyping, combined with concurrent metabolic, body composition and quality of life assessments, marks it as one of the most detailed portraits to date of what exercise does inside the bodies of women fighting breast cancer, and it lays the groundwork for the larger randomised trials that will determine whether training through chemotherapy can genuinely sharpen the immune system’s anti-tumour arsenal.

Subject of Research: Exercise training during chemotherapy for early-stage breast cancer and its effects on immune and metabolic outcomes

Article Title: Exploring the feasibility of exercise training during (neo)adjuvant chemotherapy in women with early-stage breast cancer: a pilot study examining immune and metabolic outcomes

Article References: Crespo-García, C., Bettariga, F., Taaffe, D. R., Campbell, J. P., Peddle-McIntyre, C. J., Jeffery, E., Redfern, A. D., Rinaldi, C. A., Galvao, D. A., & Newton, R. U. (2026). Exploring the feasibility of exercise training during (neo)adjuvant chemotherapy in women with early-stage breast cancer: a pilot study examining immune and metabolic outcomes. Supportive Care in Cancer, 34(10), Article 1013. https://doi.org/10.1007/s00520-026-11179-8

Image Credits: AI Generated

DOI: 10.1007/s00520-026-11179-8

Keywords: breast cancer, chemotherapy, exercise oncology, CD8 T cells, immune modulation, insulin resistance, body composition, quality of life, cancer fatigue, pilot study, resistance training, aerobic exercise