Persistent Hair Growth During Treatment With the EGFR Inhibitor Erlotinib

Erlotinib, an EGFR inhibitor used for treating epithelial malignancies, was observed to cause trichomegaly, a side effect characterized by excessive hair growth, particularly of the eyelashes and scalp. Unlike other cutaneous side effects of EGFR inhibitors, such as acneiform rash, which are temporary, trichomegaly persisted in some patients. This persistence was noted even in patients whose tumors responded positively to the treatment, suggesting a potential therapeutic use of EGFR inhibitors for stimulating hair growth. The exact mechanism behind this phenomenon remained unclear, warranting further investigation.