Sex Differences Emerge in Survival Gains From Immunotherapy for Advanced NSCLC
Immune checkpoint inhibitors have become a standard option for advanced non-small cell lung cancer without targetable driver mutations, yet the size of benefit may not be identical in men and women. A new meta-analysis pooled evidence from 42 phase 3 randomized controlled trials and found that ICI therapy improved overall survival and progression-free survival in both sexes, while the magnitude of benefit was consistently larger in males.
The analysis drew from 63 publications and included 25,827 patients, of whom 18,772 were male and 7,055 were female. That imbalance alone matters, because the female subgroup was much smaller across the trial set, with a median sample size per trial of 116 women versus 380 men. Trials were drawn from first-line and later-line settings, and most patients had good performance status, so the findings reflect a broad but still trial-selected population rather than the full spectrum of advanced disease seen in practice.
Survival Benefit Was Present in Both Sexes, but Not to the Same Degree
The pooled results were directionally favorable across the board. In men, ICIs reduced the risk of death versus chemotherapy with an overall survival hazard ratio of 0.74 and improved progression-free survival with a hazard ratio of 0.59. In women, the corresponding hazard ratios were 0.83 for overall survival and 0.76 for progression-free survival. Both sexes benefited, but the separation between the two groups was hard to ignore.
A direct treatment-by-sex interaction analysis confirmed the difference. The pooled interaction hazard ratio favored men for overall survival at 0.90 and for progression-free survival at 0.82, both reaching statistical significance. In plain clinical terms, men derived a larger relative gain from checkpoint blockade than women did, especially for disease control before progression.
The pattern was not uniform across all treatment strategies. Sex-based differences in overall survival reached statistical significance in the subgroup receiving ICI monotherapy, including anti-PD-1 monotherapy and patients with PD-L1 expression of at least 50%. Those signals weakened after false discovery rate correction for the survival endpoint, but the progression-free survival differences persisted after adjustment in the monotherapy and PD-L1–high subgroups. In contrast, no meaningful sex-based differences appeared when ICIs were combined with chemotherapy.
That distinction is clinically important. Combination regimens may blunt biologic differences that become more visible when immunotherapy is used alone.
Monotherapy Appears to Expose the Sex Gap More Clearly
The subgroup findings suggest that the sex effect, if real, may be most visible when the immune system carries more of the therapeutic burden. Monotherapy leaves less room for chemotherapy to compensate for underlying differences in tumor immunogenicity, immune activation, or host response. Combination regimens may level that field, which could explain why the sex gap largely disappeared when chemotherapy entered the treatment plan.
The biology is plausible even if the clinical explanation is incomplete. Preclinical work has linked sex hormones to regulation of the PD-1/PD-L1 axis, and prior tumor studies have pointed to sex-specific differences in antitumor immunity and immune evasion. Those mechanisms could shape how tumors respond to checkpoint blockade, particularly in the setting of high PD-L1 expression where immune escape pathways are already active.
Still, the size of the effect should be interpreted carefully. The authors used random-effects models, accounted for heterogeneity, and applied false discovery rate correction for subgroup testing, but the underlying evidence remains constrained by trial design. Female patients were underrepresented across the RCTs, and baseline imbalances could influence pooled estimates even when statistical methods are rigorous.
Heterogeneity, Not Certainty, Defines the Current Signal
Heterogeneity was present in the pooled analyses, especially for progression-free survival. That is not surprising in a dataset spanning multiple drugs, treatment lines, tumor histologies, and geographic regions. Some trials studied first-line treatment, others later-line therapy; some used ICI monotherapy, others added chemotherapy; and patient mix varied by smoking history, PD-L1 expression, and histologic subtype.
The meta-analysis also tested robustness in several ways. Investigators performed leave-one-out analyses and excluded trials with critically low numbers of female participants. Those sensitivity analyses were designed to see whether one outlying study or a sparsely represented subgroup was driving the entire signal. The overall pattern held, which strengthens the conclusion that the male-female difference is not a statistical artifact from a single trial.
Yet the result still stops short of proving that sex alone determines immunotherapy efficacy. Other variables travel with sex in lung cancer populations, including smoking exposure, tumor biology, and baseline immune competence. Even the better-performing male subgroup may partly reflect these overlapping features rather than sex as an isolated predictor.
What the Trial Set Means for Daily Oncology Practice
For oncologists treating advanced NSCLC, the immediate message is not to alter treatment solely on the basis of sex. ICIs remained superior to chemotherapy in both men and women, and the meta-analysis does not justify withholding immunotherapy from female patients who otherwise meet treatment criteria. The more defensible interpretation is that sex may influence the expected magnitude of benefit, particularly with monotherapy, and that future trials should be built to detect that difference prospectively.
The dataset itself points to why this question has remained unsettled. Many studies were not designed around sex-based hypotheses, and the number of women in individual trials was often small. The median follow-up of 26 months helps, but it does not erase the limitations created by imbalance in enrollment. When a biological signal emerges from a skewed evidence base, the result deserves attention and caution in equal measure.
This is also a reminder that biomarker interpretation in NSCLC remains incomplete. PD-L1 expression still matters, but it may not capture the full story. Sex, smoking status, immune contexture, and treatment setting may all modulate response, and those layers are not interchangeable.
The next step is not another retrospective pooling exercise alone. What is needed are randomized trials or prospectively planned analyses that enroll enough women to estimate treatment effects with greater precision, especially in ICI monotherapy and anti-PD-1 settings. Until then, the most solid conclusion is narrow but clinically relevant: immune checkpoint inhibitors improve survival in both sexes, yet the progression-free survival advantage appears attenuated in women compared with men when immunotherapy is given alone. The remaining uncertainty lies in how much of that gap is biologic, how much is confounded by trial composition, and whether future studies can isolate the difference cleanly enough to change practice.