Erlotinib is a medication primarily used to treat certain types of cancer, particularly non-small cell lung cancer and pancreatic cancer. It works by inhibiting a specific protein called epidermal growth factor receptor (EGFR), which is involved in the growth and spread of cancer cells. By blocking this protein, erlotinib can help slow down or stop the progression of the disease. This drug is usually taken in pill form and is often prescribed for patients whose cancer has specific mutations in the EGFR gene. While it can be effective, erlotinib may also cause side effects, including skin rashes and diarrhea, which should be monitored by healthcare professionals during treatment.