Systemic Therapy & Radiation for Cutaneous Malignancies
A growing subset of cutaneous malignancies exceeds the reach of surgery alone. This article reviews FDA-approved systemic therapies and radiation indications across the five major cutaneous malignancies encountered by Mohs surgeons: BCC (hedgehog pathway inhibitors, cemiplimab), CSCC (cemiplimab, pembrolizumab), MCC (avelumab, pembrolizumab), melanoma (PD-1 inhibitors, BRAF/MEK inhibitors, ipilimumab), and DFSP (imatinib). For each agent, mechanism of action, dosing, response rates, key adverse effects, and monitoring requirements are detailed. A dedicated section addresses radiation therapy indications including definitive, adjuvant, and salvage settings. The article also covers immune-related adverse event recognition and graded management, with particular attention to dermatologic irAEs relevant to the Mohs surgeon.
By Dr. Yehonatan Kaplan (M.D., Fellow ACMS)·Published: 2026-03-13·Updated: 2026-03-15·Reviewed: 2026-03-13
systemic therapyimmunotherapycheckpoint inhibitorshedgehog inhibitorsradiation therapyvismodegibcemiplimabpembrolizumabavelumabimatinibBRAFadvanced BCCadvanced CSCCMerkel cell carcinomamelanomaDFSPimmune-related adverse events
Key Takeaways
- PD-1 inhibitors (cemiplimab, pembrolizumab) are first-line systemic therapy for advanced CSCC. Exception: organ transplant recipients.
- Hedgehog pathway inhibitors (vismodegib, sonidegib) are first-line for advanced BCC. Cemiplimab is second-line after HHI failure or if HHI is inappropriate.
- Sonidegib is NOT approved for metastatic BCC in the US — only vismodegib and cemiplimab carry this indication.
- Immune-related cutaneous AEs are the most common irAEs. Graded management (topical → systemic steroids → hold CPI → biologics) prevents unnecessary treatment discontinuation.
- BRAF monotherapy increases secondary SCC risk by 12%. Always combine with a MEK inhibitor.
Overview
Mohs micrographic surgery achieves cure rates exceeding 99% for primary cutaneous malignancies and 94–97% for recurrent tumors. However, a small but clinically significant proportion of skin cancers present as locally advanced, unresectable, or metastatic disease that requires systemic therapy, radiation, or both. The Mohs surgeon must understand these modalities for three reasons: (1) to counsel patients with advanced disease about the full spectrum of treatment options, (2) to coordinate multidisciplinary care with medical and radiation oncology, and (3) to recognize and manage the cutaneous adverse effects of systemic agents that increasingly present to dermatology clinics. Over the past decade, immune checkpoint inhibitors and targeted therapies have transformed the treatment of advanced skin cancer, replacing cytotoxic chemotherapy as first-line therapy for most indications.
FDA-Approved Agents by Tumor Type
The following table summarizes currently FDA-approved systemic therapies organized by cutaneous malignancy. Approval status is current as of early 2026.
| Tumor | Drug Class | Agent(s) | Setting |
|---|---|---|---|
| BCC | SMO inhibitor (HHI) | Vismodegib 150 mg PO daily | laBCC and mBCC |
| BCC | SMO inhibitor (HHI) | Sonidegib 200 mg PO daily | laBCC only (not approved for mBCC in the US) |
| BCC | PD-1 inhibitor | Cemiplimab 350 mg IV q3wk | laBCC/mBCC after HHI or if HHI inappropriate |
| CSCC | PD-1 inhibitor | Cemiplimab 350 mg IV q3wk | laCSCC/mCSCC not curable by surgery or RT |
| CSCC | PD-1 inhibitor | Pembrolizumab 200 mg IV q3wk or 400 mg q6wk | laCSCC/mCSCC not curable by surgery or RT |
| MCC | PD-L1 inhibitor | Avelumab 800 mg IV q2wk | Metastatic MCC |
| MCC | PD-1 inhibitor | Pembrolizumab 200 mg IV q3wk | Recurrent/metastatic MCC |
| Melanoma | PD-1 inhibitor | Pembrolizumab, Nivolumab | Adjuvant (stage III/IV) and unresectable/metastatic |
| Melanoma | CTLA-4 inhibitor | Ipilimumab ± Nivolumab | Unresectable/metastatic melanoma |
| Melanoma | BRAF inhibitor | Vemurafenib, Dabrafenib, Encorafenib | BRAF V600-mutant melanoma |
| Melanoma | MEK inhibitor | Trametinib, Cobimetinib, Binimetinib | Combined with BRAF inhibitor |
| DFSP | TKI (PDGFR) | Imatinib 400–800 mg PO daily | Unresectable, recurrent, or metastatic DFSP |
Hedgehog Pathway Inhibitors
Basal cell carcinoma is driven by constitutive activation of the Hedgehog (Hh) signaling pathway, most commonly through loss-of-function mutations in PTCH1 or gain-of-function mutations in SMO. In the normal state, PTCH1 tonically inhibits SMO. Binding of Sonic Hedgehog (SHH) ligand to PTCH1 releases this inhibition, activating SMO and downstream GLI transcription factors that drive cell proliferation. In sporadic BCC, somatic PTCH1 mutations are found in approximately 70–90% of tumors. Vismodegib and sonidegib are oral small-molecule SMO inhibitors that block this pathway regardless of the upstream mutation.
Vismodegib
Vismodegib was the first FDA-approved hedgehog pathway inhibitor (2012). The ERIVANCE BCC trial demonstrated an objective response rate (ORR) of 60–69% in locally advanced BCC and 37–45% in metastatic BCC. Dosing is 150 mg orally once daily, continued until disease progression or intolerable toxicity. Common adverse effects include muscle spasms (the most frequent), dysgeusia (taste disturbance), alopecia, weight loss, and fatigue. Drug interactions involve CYP450 enzymes and P-glycoprotein inhibitors.
Sonidegib
Sonidegib was approved based on the BOLT trial for locally advanced BCC (ORR 56% at 200 mg). It is not approved for metastatic BCC in the United States (ORR only 7%). Dosing is 200 mg orally once daily. The adverse effect profile is similar to vismodegib, with the addition of CK (creatine kinase) elevation requiring laboratory monitoring.
Prescribing Precautions
Both agents are pregnancy category X: embryotoxic and teratogenic. Female patients require contraception during treatment and for 24 months (vismodegib) or 20 months (sonidegib) after cessation. Pregnancy testing is mandatory. Patients cannot donate blood during treatment or for 24 months afterward. Males cannot donate semen during treatment or for 3 months after.
PD-1 and PD-L1 Immune Checkpoint Inhibitors
PD-1 (programmed cell death protein 1) is an inhibitory receptor on T cells. PD-L1 (programmed death-ligand 1) is expressed on tumor cells and binds PD-1 to suppress anti-tumor immunity. Monoclonal antibodies targeting PD-1 (cemiplimab, pembrolizumab, nivolumab) or PD-L1 (avelumab, atezolizumab) block this interaction, reactivating T cell-mediated tumor killing. These agents have become first-line systemic therapy for advanced CSCC, second-line for advanced BCC, and first-line for metastatic MCC.
Cemiplimab for CSCC
Cemiplimab was the first FDA-approved systemic therapy for advanced CSCC (2018). In the pivotal EMPOWER-CSCC-1 trial, cemiplimab achieved an ORR of 46% in patients with locally advanced or metastatic CSCC not curable by surgery or radiation. Dosing is 350 mg IV every 3 weeks. The neoadjuvant setting is rapidly evolving: a phase 2 study demonstrated pathologic complete response in 51% and major pathologic response in 13% of patients with resectable stage II–IV CSCC who received neoadjuvant cemiplimab before surgery. Adjuvant cemiplimab for high-risk resected CSCC has also shown disease-free survival benefit.
Pembrolizumab for CSCC
Pembrolizumab received FDA approval for advanced CSCC based on the KEYNOTE-629 trial, demonstrating an ORR of approximately 35% in recurrent or metastatic disease. Dosing is 200 mg IV every 3 weeks or 400 mg IV every 6 weeks.
Cemiplimab for BCC
Cemiplimab is FDA-approved for locally advanced and metastatic BCC in patients previously treated with a hedgehog pathway inhibitor or for whom HHI is not appropriate (ORR ~29%). This serves as an important second-line option after HHI failure or intolerance. Patients unable to swallow oral medications (e.g., those with PEG tubes) are considered HHI-inappropriate, making cemiplimab the appropriate first systemic agent.
Avelumab and Pembrolizumab for MCC
Avelumab (anti-PD-L1) was approved based on the JAVELIN Merkel 200 trial, demonstrating an ORR of 32% in chemotherapy-refractory metastatic MCC with durable responses ongoing in 82% of responders at median 10.4 months follow-up. Pembrolizumab is approved for recurrent, locally advanced, or metastatic MCC. Both are first-line systemic options for metastatic MCC. For local/regional MCC where curative surgery and radiation are not feasible, immune checkpoint blockade is an option. Chemotherapy is reserved for organ transplant recipients (OTRs) in whom checkpoint inhibitors pose an unacceptable risk of graft rejection.
BRAF and MEK Inhibitors for Melanoma
Approximately 40–50% of cutaneous melanomas harbor activating BRAF mutations, of which 90% are V600E. The MAPK signaling cascade (RAS → BRAF → MEK → ERK) drives cell survival and proliferation when constitutively activated. BRAF inhibitors (vemurafenib, dabrafenib, encorafenib) target the mutated BRAF kinase, while MEK inhibitors (trametinib, cobimetinib, binimetinib) act downstream. Combination BRAF + MEK inhibition is standard practice over BRAF monotherapy because it yields higher response rates, reduces secondary drug resistance, and decreases cutaneous toxicity including the paradoxical formation of SCCs.
Clinical Use
BRAF/MEK combination therapy achieves the highest response rates among systemic options for BRAF-mutant melanoma and may be preferred when rapid tumor response is needed. However, responses are often less durable than those achieved with immune checkpoint inhibitors. Adjuvant dabrafenib plus trametinib significantly improved relapse-free survival in stage III BRAF V600E/K-mutant melanoma in the COMBI-AD trial. Current ASCO guidelines position PD-1 inhibitors as first-line, with combination nivolumab/ipilimumab for high-risk or symptomatic disease, and BRAF/MEK inhibitors for BRAF-mutant patients who need rapid response or who have contraindications to immunotherapy.
Distinguishing Adverse Effects
Photosensitivity is common with vemurafenib but rare with dabrafenib. Pyrexia (fever) is common with dabrafenib but not vemurafenib. BRAF monotherapy carries a 12% risk of secondary cutaneous SCC formation through paradoxical MAPK pathway activation; adding a MEK inhibitor reduces this risk. Combination dabrafenib/trametinib therapy increases the incidence of pyrexia compared with dabrafenib alone. Other adverse effects of BRAF inhibitors include rash (49%), arthralgia (39%), fatigue (34%), and alopecia (26%). MEK inhibitors cause acneiform dermatitis, peripheral edema, diarrhea, and rarely cardiac, ocular, or pulmonary toxicity.
CTLA-4 Inhibition: Ipilimumab
CTLA-4 is a homolog of the costimulatory receptor CD28 on T cells but has higher binding affinity for the B7 ligand on antigen-presenting cells. When CTLA-4 outcompetes CD28 for B7 binding, the costimulatory signal is suppressed, attenuating T cell activation. Ipilimumab blocks CTLA-4, restoring the costimulatory signal and enhancing anti-tumor immunity. Combination ipilimumab plus nivolumab achieves higher response rates, progression-free survival, and overall survival compared with PD-1 monotherapy for unresectable or metastatic melanoma, at the cost of significantly more frequent and severe immune-related adverse events. Ipilimumab monotherapy is no longer preferred as adjuvant therapy due to lower efficacy and higher toxicity (notably hypophysitis) compared with PD-1 monotherapy. Ipilimumab adverse events are dose-related, unlike PD-1 irAEs which are not dose-related. The most common treatment-related adverse event is fatigue; the most common irAE is rash, followed by enterocolitis and endocrinopathies.
Imatinib for DFSP
Dermatofibrosarcoma protuberans (DFSP) harbors a characteristic t(17;22)(q22;q13) translocation that fuses the COL1A1 gene with the PDGFRβ gene, resulting in constitutive PDGFR signaling. Imatinib mesylate, a tyrosine kinase inhibitor targeting PDGFR (and also BCR-ABL and KIT), is FDA-approved for unresectable, recurrent, and metastatic DFSP. A systematic review of 152 patients demonstrated complete response in 5%, partial response in 55%, and stable disease in 28%, with no difference between 400 mg and 800 mg daily doses. Adverse events occurred in at least 74% of cases, with severe events in 15%. NCCN guidelines include consideration of imatinib as neoadjuvant therapy for patients where resection would not achieve clear margins without unacceptable functional or cosmetic impairment. Tumors lacking the COL1A1-PDGFB translocation (approximately 5–10% of DFSP) may not respond to imatinib.
Immune-Related Cutaneous Adverse Events
The skin is the most frequent target of immune-related adverse events (irAEs). Mohs surgeons and dermatologists are uniquely positioned to recognize and manage these reactions, which occur in a predictable temporal pattern after checkpoint inhibitor initiation.
| irCAE | Typical Onset | Grade 1–2 Management | Grade 3+ Management |
|---|---|---|---|
| Maculopapular rash | 4–6 weeks | TCS; oral steroids if grade 2 | Hold CPI; prednisone 0.5–2 mg/kg/day; infliximab if refractory |
| Lichenoid eruption | 7–12 weeks | High-potency TCS; hold CPI + oral steroids if grade 2 | Hold CPI; systemic steroids; infliximab/tocilizumab if refractory |
| Bullous pemphigoid | 13–15 weeks | High-potency TCS; oral steroids if grade 2 | Hold CPI; systemic steroids; rituximab if refractory |
| Psoriasiform rash | 0–3 weeks | High-potency TCS; NB-UVB or apremilast | Hold CPI; biologics or retinoids |
| Pruritus | 4–6 weeks | TCS; GABA analogs (gabapentin/pregabalin) | Hold CPI; omalizumab or dupilumab |
| Vitiligo-like depigmentation | 7–9+ weeks | Photoprotection; no treatment needed | Photoprotection (does not require CPI hold) |
| SJS/TEN/DRESS | Any time | N/A (always grade 3+) | Discontinue CPI; hospitalization; IV steroids; cyclosporine |
Timeline and Patterns
Maculopapular rash typically appears within 4–6 weeks of treatment initiation. Lichenoid eruptions develop at 7–12 weeks. Bullous pemphigoid emerges later, at 13–15 weeks. Vitiligo-like depigmentation begins around 7–9 weeks and may persist indefinitely. Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS are rare but can occur at any time. Psoriasiform eruptions tend to appear early (0–3 weeks). Alopecia is a late effect, typically appearing after 13 weeks.
Graded Management
Management follows CTCAE grading principles. Grade 1 irAEs (mild) are managed with topical corticosteroids while continuing checkpoint inhibitor therapy. Grade 2 irAEs (moderate) typically require oral corticosteroids (prednisone 0.5–1 mg/kg/day); the checkpoint inhibitor can usually continue. Grade 3 and above irAEs mandate holding the checkpoint inhibitor until resolution to grade 0–1, with systemic corticosteroids at 0.5–2 mg/kg/day. Biologics (infliximab, tocilizumab) are considered for steroid-refractory grade 3+ reactions. Stevens-Johnson syndrome, TEN, and DRESS require checkpoint inhibitor discontinuation, hospitalization, and urgent dermatology consultation.
Radiation Therapy
Radiation therapy (RT) serves as definitive, adjuvant, or salvage treatment for cutaneous malignancies depending on the clinical scenario. The Mohs surgeon must understand RT indications to guide appropriate multidisciplinary referrals.
CSCC Radiation Indications
For low-risk CSCC, RT is reserved for patients who are not surgical candidates. For high-risk CSCC, indications include: definitive RT when surgery is not feasible, positive margins not amenable to re-resection, and adjuvant RT for extensive perineural invasion (PNI), large or named nerve involvement, or other high-risk features. In the setting of nodal disease, RT is indicated for inoperable or incompletely resected nodes, and as adjuvant therapy for multiple positive nodes, large nodes (>3 cm), or extracapsular extension (ECE). Protracted fractionation schedules improve cosmetic outcomes and should be used for poorly vascularized or cartilaginous areas. Chemosensitizers (cisplatin, cetuximab) may be combined with RT for advanced disease.
BCC Radiation Indications
RT for low-risk BCC is reserved for non-surgical candidates. For high-risk BCC, RT serves as definitive therapy when surgery is not feasible, salvage therapy for positive margins when further surgery is not possible, and adjuvant therapy for extensive PNI or large/clinical nerve involvement.
MCC Radiation
RT plays a larger role in MCC than in other cutaneous malignancies. For local MCC, RT may be considered for positive or narrow margins, lymphovascular invasion, or positive sentinel lymph node biopsy. In patients with one or more risk factors (tumor >2 cm, chronic immunosuppression, head/neck primary, LVI), adjuvant RT to the primary site is recommended after narrow-margin excision. RT monotherapy is an option when complete excision is not possible. For nodal MCC, RT to the nodal basin is an alternative to complete lymph node dissection following positive SLNB.
Melanoma Radiation
RT for melanoma is primarily used for brain metastases (stereotactic radiosurgery or whole-brain radiation). Adjuvant RT to the primary site or nodal basin is not standard practice but may be considered in selected high-risk cases with positive margins or bulky nodal disease.
Contraindications
Absolute contraindication: genetic conditions predisposing to skin cancer (basal cell nevus syndrome/Gorlin syndrome). Relative contraindications include connective tissue disease (increased risk of radiation toxicity) and re-irradiation within a prior radiation field for recurrent disease.
Special Populations: Organ Transplant Recipients
Organ transplant recipients (OTRs) represent a uniquely challenging population in cutaneous oncology. Their chronic immunosuppression drives dramatically elevated skin cancer risk — CSCC incidence is 65–250 times higher than the general population, and these tumors behave more aggressively with higher rates of recurrence, metastasis, and mortality. The standard first-line systemic agents (PD-1/PD-L1 inhibitors) pose a significant risk of graft rejection in OTRs. Reported rejection rates with checkpoint inhibitors in transplant recipients range from 37–54%, with frequent graft loss. Therefore, immune checkpoint inhibitors should generally be avoided in OTRs, or used only after careful risk-benefit discussion with transplant medicine and with close monitoring. For advanced CSCC in OTRs, alternatives include cetuximab (EGFR inhibitor, not FDA-approved for CSCC), capecitabine, cisplatin-based regimens, and radiation therapy. For MCC in OTRs, chemotherapy remains the first-line systemic option rather than checkpoint blockade. Immunosuppression reduction, when feasible, is an important adjunctive strategy.
Treatment Algorithms
The following algorithm summarizes the systemic therapy decision framework for each major cutaneous malignancy.
Advanced BCC Algorithm
First-line: hedgehog pathway inhibitor (vismodegib or sonidegib for laBCC; vismodegib only for mBCC). If HHI failure, intolerance, or contraindication: cemiplimab. If progression on cemiplimab: clinical trial or radiation (if not previously irradiated). Patients unable to take oral medications (e.g., PEG tube): cemiplimab is appropriate first-line because HHI is not feasible.
Advanced CSCC Algorithm
First-line (immunocompetent): cemiplimab or pembrolizumab for laCSCC/mCSCC not curable by surgery or radiation. After CPI failure: clinical trial, EGFR inhibitors (cetuximab), capecitabine, or cisplatin-based chemotherapy (none FDA-approved for CSCC). First-line (OTRs): cetuximab, chemotherapy, or radiation. Neoadjuvant: cemiplimab is emerging as a neoadjuvant option for resectable high-risk CSCC. Adjuvant: cemiplimab improves disease-free survival in high-risk resected CSCC.
Advanced MCC Algorithm
Local/regional (curative surgery/RT not feasible): pembrolizumab or avelumab. Metastatic MCC (immunocompetent): avelumab or pembrolizumab first-line. Metastatic MCC (OTR): chemotherapy first-line. Adjuvant RT to primary site or nodal basin per risk factors.
Advanced Melanoma Algorithm
Adjuvant (stage III resected): pembrolizumab or nivolumab; dabrafenib/trametinib if BRAF V600 mutant. Unresectable/metastatic: PD-1 inhibitor (pembrolizumab or nivolumab) first-line; nivolumab + ipilimumab for high-risk or symptomatic disease; BRAF/MEK inhibitors for rapid response in BRAF-mutant tumors.
Frequently Asked Questions
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References
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About This Article
Author: Dr. Yehonatan Kaplan, M.D., Fellow ACMS
Last Medical Review:
Audience: Dermatologic Surgeons
Clinic: Kaplan Clinic · DermUnbound Research Program