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10 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
DCIS is abnormal cells confined to the milk ducts of the breast; it is not yet invasive cancer and cannot spread, but some would become invasive if left. Lumpectomy with radiotherapy, or mastectomy, halves local recurrence, so the live question is which low-risk DCIS can safely be watched: the COMET trial (2024) found active monitoring no worse at two years.
Ductal carcinoma in situ is a non-obligate precursor of invasive breast cancer: neoplastic epithelial cells fill the ducts without breaching the basement membrane. It is almost always detected as microcalcifications on screening mammography, is graded low, intermediate or high by nuclear grade and necrosis, and is characterised by ER, PR and HER2 status. Natural-history data from misdiagnosed or untreated cases and from autopsy series show that a substantial share of low-grade DCIS never progresses, which makes overdiagnosis and overtreatment the central problem of the disease.
Standard treatment is breast-conserving surgery with clear margins (2 mm) followed by whole-breast radiotherapy, which halves local recurrence (about half of recurrences being invasive) without affecting survival, or mastectomy for extensive disease; sentinel node biopsy is done only with mastectomy or suspicion of invasion. Adjuvant endocrine therapy (tamoxifen, or an aromatase inhibitor in postmenopausal women per NSABP B-35 and IBIS-II DCIS) reduces ipsilateral and contralateral events in ER-positive DCIS. Genomic assays (Oncotype DX DCIS Score, DCISionRT) and clinicopathological tools help identify women who can omit radiotherapy. Three randomised trials test active monitoring against surgery for low-risk DCIS: COMET (US; JAMA, December 2024) reported that active monitoring was non-inferior for the two-year rate of ipsilateral invasive cancer, LORIS (UK) and LORD (Netherlands, now including a patient-preference cohort) continue to follow patients. Longer follow-up is needed before monitoring becomes routine, but the results have already changed how DCIS is discussed with patients.
| Setting | Approach | Guideline |
|---|---|---|
| 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). | NCCN Category 1 (radiotherapy after lumpectomy) |
| Extensive or multicentric DCIS | Mastectomy with sentinel node biopsy and optional reconstruction; radiotherapy not needed after mastectomy with clear margins. | not mapped |
| 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). | NCCN Category 1 (tamoxifen); Category 2A (aromatase inhibitor) |
| 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. | not mapped |