Table 2.

Definition of tumour outcome based on histology or clinical information

Outcome and scenario	No of tumours
Benign
B1: Surgery, benign histology	2065
B2: No surgery, no spontaneous resolution, last visit ≥10 months, SA at every visit up to 10-14 months was probably benign or certainly benign	911
B3: Spontaneous resolution	465
Malignant
M1: Surgery within 120 days, malignant histology	956*
M2: Surgery after 120 days, malignant histology, SA at every visit up to surgery was probably borderline/malignant or certainly borderline/malignant	18*
M3: No surgery, no spontaneous resolution, last visit ≥10 months, SA at every visit up to 10-14 months was probably borderline/malignant or certainly borderline/malignant	4†
Uncertain
U1: Surgery after 120 days, malignant histology, SA not probably borderline/malignant or certainly borderline/malignant at every visit up to surgery	19*
U2: No surgery, no spontaneous resolution, last visit ≥10 months, SA was uncertain or was inconsistent across visits up to 10-14 months	35
U3: No surgery, no spontaneous resolution, last follow-up visit was before 10 months (owing to death, withdrawal from study, or lost to follow-up)	123
U4: No information after the inclusion visit	309

SA=subjective assessment of ultrasound images.

^*In line with previous publications,¹⁰ 120 days was used as the maximum interval between inclusion and surgery. When surgery was done more than 120 days after inclusion and histology was malignant, the possibility was recognised that the tumour was benign at inclusion but underwent malignant transformation. For these tumours, subjective assessment at inclusion and follow-up scans were relied on to decide whether to categorise the outcome as malignant or as uncertain.

^†For these tumours, type of malignancy could not be determined. Type of malignancy was treated as a missing value and imputed (appendix 5).