Background: QTc interval prolongation can lead to life-threatening complications such as torsade de pointes (TdP), ventricular tachycardia (VT), and sudden cardiac death (SCD). It can occur with various tyrosine kinase inhibitors (TKIs) but comparative analyses on the incidence and complication rates are scarce. We thus conducted a comprehensive analysis of TKI use and QTc prolongation in clinical practice. Methods: We retrospectively reviewed the electronic medical records of all cancer patients who were treated with TKI between 01/2005 and 12/2018 at our institution. QTc prolongation was defined as a QTc ≥ 450 ms or 460 ms among male or female patients, respectively. For each type of TKIs, we determined the administration rate and incidence of QTc interval prolongation. We also studied the frequency of QTc prolongation ≥ 500 ms, rate of increase of the QTc interval by ≥ 60 ms, and the development of complications (VT, TdP and SCD). Results: In the present study, we analyzed the data of 685 cancer patients (431 male and 254 female), including 299 patients with RCC, 188 with chronic leukemia, 55 with acute leukemia, 65 with thyroid cancer, 48 with lung cancer and 39 with GIST. These patients received 902 TKI administrations and QTc prolongation was reported in 1/3 of these (289 administrations). The highest frequency was seen with imatinib, nilotinib and dasatinib (30, 40 and 50%). Among cases of QTc prolongation, a QTc interval ≥ 500 ms was documented in 53 (18.3%) and QTc progression ≥ 60 ms in 72 (25%). Complications were found in 14 cases (5%) including VT in 9, TdP in 2 and SCD in 3 administrations. Conclusions: The current findings suggest that TKI therapy leads to QTc prolongation in 1/3 of patients on average and most commonly with the Bcr-Abl TKIs, imatinib, nilotinib and dasatinib. While SCD is rare (1%) it can still evolve and in 5% of all QTc prolongations with TKIs are potentially life-threatening. These data support recommendations for serial ECGs in cancer patients undergoing TKI therapy.