In the context of EGFR mutations in NSCLC, the term “complex” or “compound” can refer to 3 possible scenarios: 1) classical L858R or Ex19Del EGFR mutations that also harbour additional EGFR mutations (classical + rare), 2) a combination of multiple, distinct, rare EGFR mutations that co-occur on the same allele (rare + rare), or 3) a combination of both L858R and Ex19Del EGFR mutations (classical + classical). Here, EGFR is linked to non-small cell lung carcinoma.