Acute Onset of a Life-Threatening Skin Toxicity Due to Osimertinib: Severe Psoriasis Versus Toxic Epidermal Necrolysis.

Osimertinib is a third-generation irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor currently used as first-line systemic therapy for advanced EGFR mutant non-small cell lung cancer. Osimertinib is generally very well tolerated with only a 1% risk of grade 3-4 skin toxicity. Here we present a case of a 68-year-old Asian male with advanced EGFR exon 19 deletion non-small cell lung cancer. After initiation of osimertinib 80 mg daily, he had a rapid worsening of his pre-existing scaly psoriatic plaques with desquamation. Treatment was withheld while psoriasis therapy was administered. He was rechallenged on osimertinib 40 mg daily and within three days developed fever, tachycardia and widespread skin desquamation. There was an initial concern of toxic epidermal necrolysis; however, this was ultimately determined to be a severe flare of psoriasis. This case serves as a reminder that severe and potentially life-threatening complications can occur, and it is imperative to maintain a high level of vigilance for unusual toxicities of EGFR tyrosine kinase inhibitors, including Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis or psoriasis.