every scheduled visit (8 weeks) until disease progression. Cobas EGFR Mutation Test v1 and v2 (Roche, USA) was used to detect 42 mutations at EGFR gene in exons 18 to 21, including T790M mutation. Radiological assessment was performed in accordance with RECIST 1.1 criteria. Result: Twenty-seven patients were treated with osimertinib from October 2015 until December 2018. At the beginning of osimertinib treatment only 17/27 (63%) patients had detectable T790M mutation in plasma, but almost all patients 26/27 (96%) had detectable plasma EGFR activating mutations (AM). During osimertinib treatment T790M mutation was cleared from plasma in all 17 patients regardless of response to treatment. On the contrary, only 12/26 (45%) patients had AM plasma clearance. Only 3 of them had had progress at median follow up of 17.5 months, what demonstrates significantly longer progression-free survival (PFS) of patients with AM plasma clearance compared to patients without AM clearance (HR 0.19; 95% CI 0.05 e 0.70, p ¼ 0.01) (Figure 1). Of the 14 patients that progressed during the observation period all had AM reapperance in cfDNA at the time on progression, while T790M only recurred in one. Conclusion: Clearance of EGFR AM in plasma during osimertinib treatment is associated with longer PFS, while clearance of T790M has no impact on survival in our small group of patients. Dynamic changes in EGFR AM might be a useful marker of outcome in patients treated with osimertinib, but further studies are needed.

Although breast cancer is the most common disease for women, bilateral breast cancer is a rare situation. Development of a second malignancy which is the most frightening side effect, may be related with genetic predisposition or cancer treatment. Because our case is a survivor of acute lymphoblastic leukemia, development of bilateral breast cancer which occurs rarely in early ages, is discussed with the help of literature.

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