EGFR mutation

An EGFR mutation is a specific typo in a cancer cell's DNA that jams a growth switch into the on position. EGFR stands for epidermal growth factor receptor, a protein on the cell surface that normally tells a cell to divide only when the right signal arrives. When the gene for it is mutated in certain lung cancers, the switch sticks on, and the cell multiplies relentlessly even without the proper signal.

These mutations are found most often in lung adenocarcinoma, and notably more often in people who have never smoked, in women, and in patients of East Asian background. Because the abnormal EGFR protein is the engine driving the tumor, it makes an ideal target: drugs called EGFR tyrosine kinase inhibitors can block that stuck switch, often shrinking the cancer with pills taken at home rather than intravenous chemotherapy.

Testing the tumor tissue (or sometimes blood) for an EGFR mutation has therefore become a routine, essential step when an advanced lung adenocarcinoma is diagnosed, because a positive result changes the whole treatment plan. The targeted pills tend to be effective and reasonably well tolerated, though side effects such as rash and diarrhea are common.

An honest limitation: these drugs control the cancer rather than cure it, and tumors usually develop resistance over time through new mutations, after which the treatment must be adjusted.