• In situ: Latin for 'in place': abnormal cells that look like cancer but have not yet broken through the layer they started in.
• Ductal carcinoma in situ (DCIS): Breast cancer cells confined inside the milk ducts, found mostly by mammography as calcifications.
• Tumour size on a breast report, and why it differs from the scan: The size on the pathology report is the largest continuous lump of invasive cancer measured under the microscope, which is not the same as the size on the mammogram or the MRI.
• How ER and PR are scored on a breast report (Allred score, H score, and why PR is not a UK core item): The oestrogen receptor test counts stained nuclei under a microscope and reports a percentage with an intensity, sometimes summarised as an Allred score out of 8 or an H score out of 300.
• Partial-breast irradiation: Treating only the part of the breast around where the lump was, instead of the whole breast, on the grounds that almost all recurrences happen there.
• Ducts, lobules and the terminal duct lobular unit: The breast is a tree: fifteen to twenty branching duct systems, each ending in a cluster of milk-making sacs called a lobule.
• Which staging edition a breast report uses: UICC TNM 8, TNM 9 and the AJCC prognostic stage: UK breast reports stage against the UICC's 8th edition, and the dataset warns against using the American AJCC 8th instead, because the two differ.
• Nottingham grade (breast cancer grade 1, 2 and 3): The grade on a breast report is a sum of three scores: how much of the tumour still forms tubes, how ugly its nuclei are, and how many cells are caught dividing.
• Lumpectomy (breast-conserving surgery): Removing only the tumour with a rim of normal breast, keeping the breast; almost always followed by radiotherapy.
• Carcinoma in situ (CIS): Cancer cells that fill the lining layer where they started but have not broken through the basement membrane into the tissue beneath.

Biomarker results to ask for: Nuclear grade and necrosis, ER and PR status, HER2 status (not used to select therapy outside trials), Margin width (2 mm standard after breast conservation), Oncotype DX DCIS Score or DCISionRT (radiotherapy omission decisions), Extent on mammography and MRI.

Scans and tests linked to this cancer: Active surveillance, Companion diagnostics, Mammography & tomosynthesis, MRI, AI in radiology, RNA sequencing & expression profiling.

Bring copies of scan reports, pathology and blood results, and a list of every medicine and supplement.

• Localised DCIS, breast conservation: Lumpectomy to 2 mm margins followed by whole-breast radiotherapy (hypofractionated), with radiotherapy omission considered for low-risk lesions (RTOG 9804 criteria or genomic assay). (Lumpectomy (breast-conserving surgery), IMRT / IGRT (modern external beam), Oncotype DX)
• Extensive or multicentric DCIS: Mastectomy with sentinel node biopsy and optional reconstruction; radiotherapy not needed after mastectomy with clear margins. (Mastectomy, Sentinel lymph node biopsy)
• ER-positive DCIS after breast conservation: Tamoxifen (or anastrozole in postmenopausal women) for five years to reduce ipsilateral and contralateral breast events; low-dose tamoxifen is an option (TAM-01). (Tamoxifen, Endocrine therapy (SERMs, AIs, SERDs))
• Low-risk DCIS: Active monitoring with mammography every six months and optional endocrine therapy, in trials (COMET, LORIS, LORD) or after shared decision-making where guidelines allow. (Active surveillance, Mammography & tomosynthesis, Ductal carcinoma in situ (DCIS), Overdiagnosis and false alarms)

From the standard of care recorded for this cancer; which apply depends on your stage and biomarkers. Ask which the team recommends and why.