In this study, we aimed to evaluate the clinical behaviour of ET, PLAGL and elucidate their response pattern across the different applied treatment regimens.<h4>Methods</h4>We conducted an in-depth retrospective analysis of clinical and serial imaging data of 18 patients with ET, PLAGL (nine each of PLAGL1 and PLAGL2 amplified).<h4>Results</h4>Patients with PLAGL1-amplified tumours (ET, PLAGL1) had fewer relapses (3/9), while PLAGL2-amplified tumours (ET, PLAGL2) were prone to early relapse or progression (8/9) and to distant, leptomeningeal and intraventricular relapses. Here, PLAGL1 is linked to essential thrombocythemia.