The scale of the problem is considerable. According to a systematic review of cases reported between 2010 and 2020, cutaneous immune-related adverse events affect roughly 30 to 50 percent of patients receiving immune checkpoint inhibitors. The risk profile differs sharply by drug class. CTLA-4 inhibitors such as ipilimumab produce higher rates of pruritus, at 30 to 40 percent, and maculopapular rash, at 20 to 30 percent, compared with 10 to 20 percent for PD-1 and PD-L1 inhibitors, which more often trigger lichenoid reactions or vitiligo. Combination therapy with ipilimumab and nivolumab amplifies both incidence, reaching 60 to 70 percent, and severity, with rashes appearing earlier, at a median of two to four weeks versus six to twelve weeks for monotherapy.

Timing itself carries diagnostic weight. The consensus notes that cutaneous events can emerge anywhere from the start of therapy to 150 weeks afterward, and even after immunotherapy has been discontinued. Severe reactions such as erythema multiforme and toxic epidermal necrolysis tend to appear early, with a median onset near 9.5 weeks, while lichenoid eruptions and bullous pemphigoid-like disease surface later, at median onsets of 21.6 and 21.5 weeks respectively. The expert panel therefore recommends routine skin examinations every two to three weeks during the first three months of treatment, the peak period of onset, followed by monthly monitoring for high-risk patients, with all findings graded using the CTCAE v5.0 standard.

At the mechanistic level, the toxicities trace back to the biology of immune regulation. Under normal conditions, CTLA-4 restrains T-cell activation during thymic maturation, while the PD-1 pathway maintains peripheral tolerance to self-reactive T cells. When checkpoint inhibitors block these brakes, antitumor responses intensify, but self-reactive T-cell clones can proliferate concurrently, triggering autoimmune reactions. A second mechanism involves antigen cross-reactivity: in metastatic melanoma, tumor cells and epidermal melanocytes share common antigens, so an immune response aimed at the cancer can also destroy pigment cells, producing vitiligo-like reactions. Pre-existing skin damage may expose self-antigens, PD-1 blockade can activate B cells to generate autoantibodies, and genetic predisposition plays a role, with the HLA-DRB1*11:01 allele significantly associated with pruritus.

The consensus classifies cutaneous events into two broad groups: newly emerging conditions and exacerbations of pre-existing skin disease. Psoriasiform eruptions rank among the most common, arising either de novo or through flares of prior psoriasis. Histopathologically, plaque-type lesions typically show hyperkeratosis with parakeratosis, acanthosis, a diminished granular layer, and perivascular lymphocytic infiltrates with neutrophils, including Munro microabscesses or Kogoj spongiform pustules, although some patients lack these classic features. Treatment is tiered by severity: topical corticosteroids or vitamin D3 analogs for mild to moderate disease, narrowband UVB phototherapy and systemic agents such as methotrexate, retinoids, or the oral PDE-4 inhibitor apremilast for more extensive cases, and biologic agents for severe disease when tumor status is stable and an oncologist has carefully evaluated the risk.

Eczematous eruptions, more frequent with anti-CTLA-4 therapy, present acutely with erythema, papules, vesicles, erosion, and crusting, and chronically with lichenification and hyperpigmentation. Management follows the SCORAD severity index, beginning with cleansing and moisturizing for all patients, topical corticosteroids or calcineurin inhibitors with oral antihistamines for mild cases, and systemic agents such as hydroxychloroquine, thalidomide, short-term corticosteroids, dupilumab, or phototherapy for moderate to severe disease. Lichenoid eruptions, in contrast, are more strongly linked to PD-1 and PD-L1 inhibitors, favor the dorsum of the hands, extensor limb surfaces, and lower lip, and show vacuolar interface dermatitis with a band-like lymphohistiocytic infiltrate on biopsy, sometimes with eosinophils in immunotherapy-induced cases. Topical anti-inflammatory agents suffice for mild disease, while thalidomide, hydroxychloroquine, acitretin, or systemic corticosteroids serve more severe presentations.

The most dangerous end of the spectrum demands immediate action. Stevens-Johnson syndrome and toxic epidermal necrolysis produce rapidly coalescing edematous erythema, targetoid lesions, blisters, and epidermal detachment that creates a scalded appearance, frequently involving oral, ocular, and genital mucosa. For involvement of ten percent or less of body surface area without significant systemic symptoms, the consensus recommends temporary suspension of immunotherapy plus systemic corticosteroids at 0.5 to 1 mg per kilogram per day. Beyond that threshold, or with mucosal involvement, immediate permanent cessation, hospitalization, higher-dose methylprednisolone at 1 to 2 mg per kilogram per day, and intravenous immunoglobulin or cyclosporine in severe cases are required. Erythroderma, defined as erythema over more than 90 percent of body surface area, likewise warrants immediate discontinuation, typically permanent when hemodynamic instability or secondary infection complicates the picture.

Bullous pemphigoid-like eruptions, predominantly induced by anti-PD-1 and PD-L1 agents, bring tense blisters on erythematous skin and intense pruritus, and some patients develop non-bullous variants with pruritic erythema, nodules, and erosions that require immunofluorescence and serologic testing for anti-BP180 or anti-BP230 antibodies to confirm. These eruptions force permanent discontinuation of immunotherapy in 20 to 50 percent of affected patients, making early diagnosis critical. Dermatomyositis presents a particular diagnostic challenge because cancer itself predisposes patients to the condition; the panel recommends baseline dermatologic evaluation before immunotherapy and early testing for anti-TIF1γ antibodies, which correlate with severe disease and demand vigilance for rapidly progressive interstitial lung disease. In anti-TIF1γ-positive cases, immediate high-dose corticosteroids and comprehensive cancer screening are advised. Notably, vitiligo, which favors sun-exposed sites and appears most often in melanoma patients, is associated with improved oncological outcomes and should not prompt discontinuation.

Perhaps the consensus’s most distinctive contribution is its decision-making philosophy, distilled as the Two-Look and Two-Don’t principle: look at the primary rash morphology and look for visceral involvement, but do not discontinue immunotherapy prematurely and do not use rash extent as the sole criterion for stopping treatment. Eczema covering more than 30 percent of body surface area without organ involvement can often be managed without interrupting therapy, whereas Stevens-Johnson syndrome affecting under five percent still warrants immediate cessation because of progression risk. The panel also stresses that immune-related adverse events rarely respect organ boundaries. Myocarditis, though rare, carries the highest mortality of any checkpoint toxicity, with a median onset near six weeks. Pneumonitis accounts for roughly 35 to 40 percent of fatal immune-related events, and endocrine toxicities affect about ten percent of patients, requiring hormonal monitoring every four to six weeks. Multidisciplinary team assessment is recommended for all moderate to severe cutaneous events or multi-organ involvement.

Looking forward, the authors acknowledge that the precise mechanisms distinguishing these reactions from classic drug-induced dermatitis remain unresolved, and they call for early warning systems and screening strategies to reduce skin damage and treatment interruptions. They also flag a therapeutic dilemma: while no high-quality evidence shows that corticosteroids used for cutaneous events undermine immunotherapy efficacy, some data suggest high-dose steroids given for other adverse events may shorten progression-free survival. That concern is driving interest in non-immunosuppressive biologics such as dupilumab as safer alternatives for severe skin toxicity. For now, the consensus delivers a clear message to oncologists and dermatologists alike: recognize rashes early, grade them accurately, examine the whole patient, and reserve treatment discontinuation for the situations where it is genuinely lifesaving.

Subject of Research: Management of cutaneous immune-related adverse events caused by immune checkpoint inhibitor cancer therapy

Article Title: Multi-disciplinary expert consensus on cutaneous adverse events caused by immune checkpoint inhibitors (2025)

Article References: Sun, Y., Huang, J., Hu, F., Xue, R., Chang, X., Cheng, L., Cui, Y., Jiang, J., Ou, X., Deng, D., Li, X., Liang, Y., Liu, H., Long, H., Lv, X., Qiao, J., Tang, H., Wang, W., Xia, Y., … Yang, J. (2025). Multi-disciplinary expert consensus on cutaneous adverse events caused by immune checkpoint inhibitors (2025). Clinical Cancer Bulletin, 4(1), Article 16. https://doi.org/10.1007/s44272-025-00043-1

Image Credits: AI Generated

DOI: 10.1007/s44272-025-00043-1

Keywords: immune checkpoint inhibitors, cutaneous adverse events, cancer immunotherapy, dermatology, PD-1 inhibitors, CTLA-4 inhibitors, toxic epidermal necrolysis, bullous pemphigoid, dermatomyositis, psoriasiform eruptions, multidisciplinary consensus, drug toxicity

Immune checkpoint inhibitors, including antibodies that block PD-1, PD-L1 and CTLA-4, have transformed the treatment of melanoma, lung cancer and many other malignancies by releasing the molecular brakes on T cells. Yet responses are unpredictable, and researchers have long searched for modifiable factors that might explain why some patients derive extraordinary benefit while others progress rapidly. Among the candidates, vitamin D has attracted particular attention. The secosteroid hormone regulates innate and adaptive immunity, influences myeloid and lymphocyte function, and has been associated in multiple studies with better outcomes for patients receiving immunotherapy. Because vitamin D status in countries at high latitudes follows a pronounced seasonal rhythm, driven by ultraviolet B exposure and cutaneous synthesis, some investigators hypothesised that the time of year a patient starts therapy could subtly shape the immune environment in which checkpoint blockade takes effect.

Previous reports in melanoma had fuelled this idea, with conflicting evidence about whether summer initiation of ipilimumab, for example, was associated with longer survival than winter initiation. To test the hypothesis at scale, the Manchester team, led by Oliver Kennedy and Paul Lorigan, conducted a single-site retrospective review of patients treated with checkpoint inhibitors between 2018 and 2023. They categorised patients by season of treatment initiation using two complementary definitions: the broader split of October to March versus April to September, aligned with the UK’s pattern of vitamin D insufficiency, and a narrower comparison of December to February versus June to August, capturing the extremes of winter and summer. Vitamin D status was classified using standard laboratory thresholds, with sufficiency defined as serum 25-hydroxyvitamin D above 50 nmol/L, insufficiency between 25 and 50 nmol/L, and deficiency below 25 nmol/L.

The statistical machinery applied to the data was conventional but rigorous. Kaplan-Meier curves provided estimates of median overall survival and one-year survival, while Cox proportional hazards models generated adjusted hazard ratios that accounted for potential confounders. Among the 4,329 patients analysed, 2,191 deaths were recorded, giving the study substantial statistical power. The headline result was strikingly null: patients who began checkpoint inhibitors between April and September fared no better than those who started between October and March, with an adjusted hazard ratio of exactly 1.00. One-year survival was virtually identical in the two groups, at 64.9 percent versus 65.0 percent, and median overall survival differed by less than a month, at 21.3 versus 21.8 months.

Beneath that overall null result, however, the data revealed intriguing signals at the level of specific regimens and diseases. When the analysis was restricted to the narrower seasonal comparison, initiation in June to August was associated with longer overall survival than initiation in December to February for patients receiving the combination of nivolumab and ipilimumab, with an adjusted hazard ratio of 0.64, and for patients with small cell lung cancer, with an adjusted hazard ratio of 0.52. No such association was observed for other checkpoint inhibitor regimens or other cancer types. These subgroup findings suggest that if seasonal biology matters at all, its influence may be confined to particular treatment combinations or tumour contexts, a pattern that the authors caution requires confirmation in independent cohorts before any clinical conclusions are drawn.

The vitamin D measurements added a second layer to the story. Among the 1,206 patients whose vitamin D status was available, deficiency was far from rare, and it followed the expected seasonal gradient with remarkable fidelity. The proportion of deficient patients peaked at 28.4 percent in March, the tail end of the British winter when cutaneous synthesis has been minimal for months, and fell to just 3.5 percent in August, after a summer of sun exposure. That nearly tenfold seasonal swing in deficiency prevalence confirms that the study population experienced the kind of vitamin D variation that, in theory, could modulate immune function and thereby influence immunotherapy outcomes.

And vitamin D status did matter for survival. After adjustment, patients with insufficient vitamin D had a hazard ratio of 1.64 for death compared with sufficient patients, while those who were frankly deficient had a hazard ratio of 2.38. In other words, deficient patients were more than twice as likely to die over the follow-up period as those with adequate levels, a magnitude of association that rivals many established prognostic factors in oncology. Yet when the researchers examined the subgroup of vitamin D-sufficient patients, the season of treatment initiation showed no association with survival at all, undermining the hypothesis that seasonal vitamin D fluctuations are the mechanism driving any apparent seasonal survival effects.

The authors offer two possible interpretations of this pattern, and both carry important implications. The first is that the seasonal variation in vitamin D observed in the cohort, while real, was simply not large enough to alter the effectiveness of checkpoint inhibitors in a way that translates into measurable survival differences. The second, more sobering possibility is that the well-documented association between vitamin D status and immunotherapy outcomes may itself be confounded. Vitamin D levels correlate with general health, mobility, outdoor activity, nutritional status and disease burden, all of which independently influence survival. Patients who are well enough to spend time outdoors in the summer sun may simply be healthier in ways that a blood test cannot capture. If that is the case, vitamin D could be a marker of prognosis rather than a mediator of immunotherapy response, and trials of supplementation would be unlikely to improve outcomes.

Distinguishing between these explanations is precisely what the field now needs. Randomised trials of vitamin D supplementation in patients receiving checkpoint inhibitors are the cleanest way to test causality, and the new findings sharpen the rationale for such studies by showing that observational season-based approaches cannot substitute for them. The regimen-specific signals, particularly the apparent summer advantage for nivolumab plus ipilimumab and for small cell lung cancer, also merit dedicated investigation, since combination CTLA-4 and PD-1 blockade engages immune biology in ways that differ from single-agent therapy, and small cell lung cancer has a distinct immunological and epidemiological profile from most other tumours treated with checkpoint inhibitors.

For patients and clinicians, the practical message is measured. There is no evidence from this study that the timing of the year should influence when immunotherapy is started; cancer treatment should proceed on clinical grounds without regard to the calendar. At the same time, the strong association between vitamin D deficiency and poorer survival reinforces existing guidance that patients with cancer should have their vitamin D status checked and corrected where appropriate, in line with standard nutritional care. What the Manchester study removes is a seductive but unsupported idea: that Britain’s long winters might be quietly sabotaging immunotherapy. The seasons, it turns out, shape our vitamin D levels profoundly, but whether that biology shapes cancer survival remains an open and increasingly well-defined question.

Subject of Research: Seasonal variation in vitamin D status and overall survival in patients receiving immune checkpoint inhibitors

Article Title: Seasonal variations in overall survival and vitamin D status in a UK pan-cancer cohort receiving checkpoint inhibitors

Article References: Seasonal variations in overall survival and vitamin D status in a UK pan-cancer cohort receiving checkpoint inhibitors. (n.d.). https://doi.org/10.1007/s00262-026-04575-w

Image Credits: AI Generated

DOI: 10.1007/s00262-026-04575-w

Keywords: immune checkpoint inhibitors, vitamin D, overall survival, seasonality, immunotherapy, melanoma, lung cancer, nivolumab, ipilimumab, pan-cancer cohort, retrospective study, cancer outcomes