Homozygous EGFR Gain-of-Mutation in a Patient Presenting with Metachronous Non-Small Cell Lung Adenocarcinoma and Invasive Ductal Breast Carcinoma

Author(s): Hanifeh Mirtavoos-Mahyari, Ramin Ajami, Mahbuba Chowdhury, Saiji Nageshwaran, Farbod Bahreini, Hassan Vahidnezhad, Sathiji Kathiresu Nageshwaran.

The epidermal growth factor receptor (EGFR) exon-19 deletion is the most common EGFR mutation occur-ring in more than 40% of lung cancer patients. Exon-19 deletion is frequently detected in adenocarcinomas but is rare in the germline. Additionally, the occurrence of homozygous and heterozygous mutations in met-achronic cancers is uncommon. We present a 53-year-old female non-smoker diagnosed with two primary cancers; invasive ductal carcinoma and lung adenocarcinoma. A family history of breast and lung cancer was present in her sister and father, respectively. To determine the most appropriate treatment, EGFR gene sequencing was performed from the patient’s lung tissue sample and a peripheral blood sample was taken to identify the presence of EGFR mutation in the patient’s germ line. Loss-of-heterozygosity was discovered between the blood and tissue samples, with the extremely rare occurrence of a homozygous EGFR exon-19 deletion within the tumour sample.