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Epidermal growth factor receptor (EGFR) signaling plays a key role in regulating epidermal cell proliferation, survival, and differentiation. Keratins form a scaffold with epidermal desmosomes that involves ErbB/ EGFR signaling and keratin deficiency makes keratinocytes more sensitive to EGFR activation. Erlotinib, an EGFR inhibitor, was approved 20 years ago for cancer treatment and is generally used at 150 mg daily in adults \>50 kg. While gastrointestinal and cutaneous side effects commonly occur at doses of 150 mg, adverse events occur less often at lower doses. We first reported erlotinib as effective for Olmsted syndrome, a rare hereditary EDD with painful PPK that results from variants in TRPV3. Erlotinib is now the treatment of choice for children and adults with Olmsted syndrome. Erlotinib is thought to inhibit formation of a complex that includes TRPV3, EGFR, and its primary skin-based ligand, TGF-a, which in turn regulates keratinocyte proliferation and differentiation. High-throughput screening to identify compounds that stabilize keratin filaments have also pointed to the EGFR pathway for targeting. Reviews and recent case reports have suggested the benefit of erlotinib for PC, Given these preliminary data, we hypothesize that EGFR activation is a characteristic feature of keratinopathies. Further, we expect that oral low-dose erlotinib will improve the scaling and skin thickening of the spectrum of keratinopathies and be tolerated by most patients. For those who experience pain, particularly from plantar involvement, we predict that erlotinib therapy will improve mobility and pain. Finally, we aim to find the mechanism by which erlotinib improves the phenotypes of the various keratinopathies to better understand these disorders and predict response. We will look specifically at the impact on differentiation vs. hyperproliferation and barrier function, as well as the immune modulatory effects of the erlotinib using a multi-omics approach.
