Stopping rules, the table describes the number of patients at which the study arm should be put on hold
| Stoping rules | After 5 included patients per arm | After 10 included patients per arm | After 15 included patients per arm |
| 1a. Severe complications such as Clavien-Dindo grade III complications after thermal ablation and prior to surgical resection, and/or complications related to thermal ablation which interfere with surgical excision such that the surgical procedure should be deviated (eg, surgical procedure cannot be performed due to a large haematoma). | 3 patients | 3 patients | 4 patients |
| 1b. Severe complications after thermal ablation and surgery, with or without radiotherapy related to the study intervention (thermal ablation), which result in unplanned mastectomy. | 1 patient | 1 patient | 1 patient |
| 2.Premature termination of thermal ablation procedure, due to pain or discomfort because of an insufficient pain protocol (local anaesthetics with or without sedation). | 3 patients | 3 patients | 4 patients |
| 3.Irradical resection (more than focally irradical*) after thermal ablation and surgical resection, in which, a margin is considered irradical if viable or necrotic tumour tissue is found in the specimen at pathologic evaluation (R1 resection). | 3 patients | 3 patients | 4 patients |
| 4a. Missed target (ablation zone completely outside of the tumour area on MRI) on MRI 2 weeks after thermal ablation. | 3 patients | 3 patients | 4 patients |
| 4b. Incomplete ablation rate as determined on pathological examination. | 4 patients | 5 patients | 6 patients |
*An irradical resection or R1 resection is defined as viable or necrotic tumour (either invasive or DCIS) reaching in the ink in a small area (≤4 mm). The stopping rule applies to more than focally irradical tumours: viable or necrotic tumour (either invasive or DCIS) reaches the ink in a larger area (>4 mm) or in multiple smaller areas.