Milea Timbergen

164 therapies, and local therapies such as radiofrequency or cryotherapy. The category of “NS” was used when information was lacking about the type of active treatment. Shift to ‘active treatment’ is reported as the percentage of patients shifting to active treatment from each separate study, and compiled as an overall median percentage of patients shifting to active treatment with IQR, compiling all study results. The same was done for the types of active treatments. Variables such as median follow-up of the AS group, the time to intervention, the time to progression, the time to stabilisation, the time to regression, progression-free survival (PFS), and EFS were extracted in case they were stated by the included studies. Results Systematic literature search The search was performed on December 19, 2019 and updated on April 14, 2020. The search strategy yielded a total of 940 papers, after deduplication, 589 papers remained. Title and abstract were screened leading to the exclusion of 551 papers. A total of 38 papers were reviewed based on full-text and 25 studies were finally included for further analysis. The study selection procedure is depicted in Supplemental Materials 2. No randomised controlled trials reporting about AS in DTF were identified. Several reviews, discussing the current status and treatments of DTF addressed the AS approach, but none of these reviews included a systematic literature review solely focussing on the outcomes of the AS approach. Study design and quality assessment. All included studies were published after 2005. All studies were retrospective case series which are generally considered to have a high risk of bias and a low certainty 19, 20 . Of note, nine studies potentially used overlapping patient cohorts based on author names, affiliations and inclusion time period 2, 9, 14&6, 10, 12, 21-23 . 6