Cancer Immunotherapy: Dermatologic Perspectives

Introduction

Immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment, producing durable responses in previously untreatable malignancies. However, by unleashing the immune system against tumors, these agents also cause a spectrum of immune-related adverse events (irAEs), with the skin being the most commonly affected organ.

Dermatologists play a crucial role in:

Treating cutaneous malignancies with immunotherapy (melanoma, cSCC, MCC)
Managing cutaneous irAEs in patients receiving ICIs for any cancer
Recognizing when skin toxicity warrants treatment modification

Checkpoint Inhibitor Mechanisms

Immune Checkpoint Concept

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Key Checkpoints and Agents

Target	Agents	Mechanism
CTLA-4	Ipilimumab	Blocks CTLA-4 on T cells; enhances priming
PD-1	Nivolumab, Pembrolizumab, Cemiplimab	Blocks PD-1 on T cells; restores effector function
PD-L1	Atezolizumab, Durvalumab, Avelumab	Blocks PD-L1 on tumor/APCs

Combination Therapy

Combination	Example	Notes
Anti-CTLA-4 + Anti-PD-1	Ipilimumab + Nivolumab	Higher efficacy but more irAEs
ICI + targeted therapy	Pembrolizumab + lenvatinib	Melanoma, others

ICIs in Dermatologic Malignancies

Melanoma

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Setting	Agents	Response Rate
Metastatic (1st line)	Pembrolizumab or Nivolumab	40-45% ORR
Metastatic (combo)	Ipilimumab + Nivolumab	58% ORR
Adjuvant (stage III)	Pembrolizumab or Nivolumab	Reduced recurrence
Neoadjuvant	Emerging approach	High pathologic response

Cutaneous Squamous Cell Carcinoma (cSCC)

Feature	Details
Agent	Cemiplimab (anti-PD-1)
Indication	Locally advanced or metastatic cSCC not amenable to surgery/radiation
Response rate	~50% ORR
Duration	Often durable

Merkel Cell Carcinoma (MCC)

Agent	Setting	Response Rate
Avelumab	1st or 2nd line	33-62%
Pembrolizumab	1st line	~56%

Cutaneous Immune-Related Adverse Events (irAEs)

Overview

The skin is the most commonly affected organ with ICIs:

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Common Cutaneous irAEs

irAE	Frequency	Onset	Features
Maculopapular rash	30-40%	3-6 weeks	Non-specific MPE
Pruritus	20-30%	Variable	With or without rash
Vitiligo	5-10%	3-6 months	Good prognostic sign (melanoma)
Lichenoid dermatitis	5-10%	Weeks-months	Interface pattern
Psoriasiform dermatitis	5%	Variable	New or exacerbation
Bullous pemphigoid	1-2%	Months	Anti-BP180/230

Grading Cutaneous irAEs (CTCAE)

Grade	Description	Management
Grade 1	<10% BSA, no symptoms	Continue ICI; topical steroids, emollients
Grade 2	10-30% BSA, symptoms	Continue ICI; topical steroids, antihistamines
Grade 3	>30% BSA, limiting ADLs	Hold ICI; systemic steroids
Grade 4	Life-threatening (SJS/TEN, DRESS)	Permanently discontinue; high-dose steroids, hospitalize

Specific Cutaneous irAEs

Maculopapular Eruption

Feature	Details
Appearance	Erythematous macules and papules
Distribution	Trunk, extremities; may be photodistributed
Histology	Interface dermatitis ± eosinophils
Management	Topical steroids; systemic if severe

Lichenoid Reactions

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Vitiligo-like Depigmentation

Feature	Details
Incidence	5-10% of melanoma patients on ICI
Mechanism	Anti-melanocyte T cell response
Significance	Favorable prognostic sign
Distribution	Often around tumor sites, sun-exposed
Management	No treatment needed; sun protection

Bullous Pemphigoid (BP)

Feature	Details
Incidence	1-2%
Latency	Often delayed (months)
Presentation	Tense bullae, pruritus
Diagnosis	DIF: Linear IgG/C3 at BMZ
Antibodies	Anti-BP180 (more common than anti-BP230)
Management	Hold ICI; topical/systemic steroids, doxycycline

Severe Cutaneous irAEs

Potentially Life-Threatening

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Management of Severe irAEs

Severity	Action
Grade 3	Hold ICI; prednisone 0.5-1 mg/kg; dermatology consult
Grade 4	Permanently discontinue; high-dose steroids; hospitalize
SJS/TEN	Permanently discontinue; IVIG, cyclosporine, or etanercept considered
Refractory	Consider infliximab (avoid in hepatic irAE), MMF, or other immunosuppressants

Prognostic Significance of Cutaneous irAEs

Association with Outcomes

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irAE	Prognostic Association
Vitiligo	Strong positive correlation with survival in melanoma
Any cutaneous irAE	Modest positive correlation
Any irAE	Generally associated with improved response

Other Immunotherapeutic Approaches

Talimogene Laherparepvec (T-VEC)

Feature	Details
Type	Oncolytic virus (modified HSV-1)
Mechanism	Lyses tumor cells, releases antigens, expresses GM-CSF
Administration	Intralesional injection
Indication	Unresectable melanoma (stage IIIB-IV)
Local reactions	Injection site pain, erythema
Systemic effects	Flu-like symptoms

Adoptive Cell Therapy

Therapy	Mechanism	Status in Skin Cancer
TIL therapy	Tumor-infiltrating lymphocytes	FDA approved for melanoma (lifileucel)
CAR-T	Engineered T cells	Investigational for solid tumors

Summary

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Key Clinical Pearls

Topic	Pearl
Skin = #1 irAE site	30-50% of ICI patients develop cutaneous irAE
Vitiligo	Favorable prognostic sign in melanoma
BP latency	Often months after ICI initiation
Grade 3-4	Hold or stop ICI; systemic steroids
Don't stop for Grade 1-2	Most patients can continue with supportive care
Cemiplimab	FDA-approved for advanced cSCC
TIL therapy	Now FDA-approved for melanoma

Cross-References

Volume 05, Chapter 7: Biologic Therapies
Volume 18: Drug Reactions
Volume 22: Oncology - Melanoma, cSCC