D1.397 - Successfull rapid drug desensitization to cemiplimab in a patient with lung squamous cell carcinoma

BACKGROUND: Cemiplimab is an immune checkpoint inhibitor (ICI) approved by European Medicine Agency for treating certain advanced cancers. Among biological agents, it represents a rare trigger of drug hypersensitivity reaction (HR).

MATERIALS AND METHODS:

CASE REPORT

A 66-year-old woman with advanced stage squamous non- small cell lung cancer with high PD-L1 expression underwent a remote consultation to our Department due to suspicion of medical allergy.

In november 2025 she started immunotherapy with Cemiplimab 350 mg administered intravenously (IV), scheduled every three weeks; the drug infusion did not include any premedication as per local protocol.

The first infusion was well tolerated, whereas she experienced facial and back erytema, dyspnea without change in vital signs after 20 cc of the second administration. She had a complete regression of symptoms after infusion interruption and treatment with chlorphenamine 10 mg IV and hydrocortisone 1000 mg IV. In stable conditions the infusion was restarted at half the rate an hour later, after 6 cc of the drug she showed facial erytema and sense of dyspnea. The symptoms resolved with the discontinuation of the ICI.

RESULTS:

Skin tests with Cemiplimab are not performed since the patient lives in another region and she referred to our Oncology Department only for the immunotherapy, futhermore they are not well validated for this agent.

Based on the medical history we suspected an IgE-mediated HR defined as Grade 2 according to modified Brown’s Classification.

Considering the severity of reaction and the absence of any alternative therapeutic approach for the patient (data on cross-sensitivity between ICI are limited), we developed a 3-bag, 12-step rapid drug desensitization (RDD) to Cemiplimab. An individualized premedication regimen with H1 and H2 blockers, montelukast and systemic corticosteroids was included. Until now the patient has tolerated 4 RDD to Cemiplimab. The restaging CT scan after the fourth cycle of ICI demonstrated a partial response.

CONCLUSION:

HRs to cemiplimab are rare, when they occur represent a major safety concern and a significant challenge for clinicians. Drug desensitization is a therapeutic approach safely admister biologics causing a HR. To our knowledge this is the first report of successfull 12-step RDD to cemiplimab.