⁃ A. Preoperative diagnosis of DCIS, of any grade and any size if planned for mastectomy.

⁃ B. Planned Risk-reducing mastectomy, if it would be considered for upfront SLND due to institutional practice or in case of an individualised recommendation.

⁃ C. Any case with a preoperative diagnosis of pre-invasive or unclear lesion, that upfront SLND would be otherwise considered, such as, but not limited to:

• Patients with a preoperative diagnosis of DCIS grade 3 any size or, DCIS grade 2 larger than or equal to 20 mm on mammography and planned for breast conserving surgery or

• Patients with a preoperative diagnosis of DCIS on core biopsy with a palpable mass on clinical examination or mass effect on radiology or

• Patients with a preoperative diagnosis of DCIS with suspicion of micro-invasion on core biopsy or

• Patients with a mammographic/ultrasound/MRI finding, suspicious for breast cancer (BIRADS 4 or 5) planned for diagnostic excision with breast conserving surgery, with no definitive diagnosis of invasive cancer or

• Patients with a preoperative diagnosis of DCIS, any grade, any size and planned for a complex oncoplastic procedure or

• Patients with a preoperative diagnosis of DCIS, any grade, any size and planned for a procedure that may compromise detection rate for a future SLND, such as, but not confined to: lesions in the upper outer quadrant or the axillary tail, removal of the nipple areola complex and so on or

• The above mentioned categories with a preoperative diagnosis of pleomorphic Lobular Cancer in Situ (pLCIS), classic Lobular Neoplasia (LN) or Atypical Ductal Hyperplasia (ADH).