# Ductal carcinoma in situ (DCIS)

Source: https://onco.cc/cancers/ductal-carcinoma-in-situ/  
OnCo record `ductal-carcinoma-in-situ` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

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.

## Summary

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.

The frontier is a risk-stratified approach in which high-grade or HER2-positive DCIS is treated fully while low-risk lesions are watched, informed by molecular classifiers and, potentially, by preventive vaccines against HER2 or other DCIS antigens.

## Fields

- Kind: Cancer
- Last checked: 2026-09-10
- Also known as: DCIS; Stage 0 breast cancer; Pre-invasive breast cancer; Intraductal carcinoma
- Tags: nci-coverage; breast; overdiagnosis
- Group: breast
- Burden: About one in five to one in four breast cancers detected by mammographic screening is DCIS; it was rare before screening and is now diagnosed in tens of thousands of women a year in the US alone (SEER; NCI).
- Subtypes: Low-grade DCIS (often ER-positive); Intermediate-grade DCIS; High-grade DCIS with comedo necrosis (often HER2-positive); DCIS with microinvasion (staged as T1mi); Paget disease of the nipple (DCIS extending to nipple skin)
- Biomarkers: 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

## Sections of this record

The page is a hub with ten sections in reading order; large sections have their own page. The same plan as JSON: https://onco.cc/api/v1/cancers/ductal-carcinoma-in-situ/sections.json

- Overview (on the hub): The TL;DR, the family this cancer belongs to, the organ, who gets it and what the state of the art is. https://onco.cc/cancers/ductal-carcinoma-in-situ/#overview [4 state-of-the-art points]
- What it is (on the hub): Anatomy, the subtypes and how they differ, how it is staged, and where advanced disease spreads. https://onco.cc/cancers/ductal-carcinoma-in-situ/#what-it-is [5 subtypes]
- Finding it (on the hub): How it shows itself, how it is confirmed, what screening exists, and the biomarkers clinicians test for. https://onco.cc/cancers/ductal-carcinoma-in-situ/#finding-it [6 biomarkers]
- Treating it (on the hub): The standard of care by setting, the medicines, surgery and radiotherapy named in it, and the regimens behind them. https://onco.cc/cancers/ductal-carcinoma-in-situ/#treating-it [4 settings, 3 decisions with options]
- Evidence (on the hub): Trials recruiting now, the landmark trials, the key papers and what they mean, the latest literature, and the milestones year by year. https://onco.cc/cancers/ductal-carcinoma-in-situ/#evidence [4 trials, 1 key paper, 7 milestones]
- The science (on the hub): The molecular landscape: the targets and how often each appears, the pathways, the mechanics stages and the preclinical models. https://onco.cc/cancers/ductal-carcinoma-in-situ/#science [3 targets, 1 pathway]
- Where you are (own page): Cases by country, the UK and NHS pathway and other country lenses, and the expert centres with trials on record. https://onco.cc/cancers/ductal-carcinoma-in-situ/where-you-are/
- Living with it (on the hub): The decisions you may face, the aids that walk through them, the warnings on record, the first sixty days and the questions to ask. https://onco.cc/cancers/ductal-carcinoma-in-situ/#living-with-it [15 questions, 3 red cards]
- What is coming (own page): Everything in development, the open problems and what is being done about them, the roadmaps, and what changed on this record. https://onco.cc/cancers/ductal-carcinoma-in-situ/coming/ [4 medicines, 4 trials, 4 open problems]
- Data (own page): Every connected record, the notes, the JSON, Markdown and RDF twins, and where the record came from and when it was checked. https://onco.cc/cancers/ductal-carcinoma-in-situ/data/ [44 connected records]

## Standard of care

- 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)](https://onco.cc/terms/lumpectomy/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Oncotype DX](https://onco.cc/drugs/oncotype-dx/))
- Extensive or multicentric DCIS: Mastectomy with sentinel node biopsy and optional reconstruction; radiotherapy not needed after mastectomy with clear margins. ([Mastectomy](https://onco.cc/terms/mastectomy/), [Sentinel lymph node biopsy](https://onco.cc/technologies/sentinel-node/))
- 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](https://onco.cc/drugs/tamoxifen/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/))
- 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](https://onco.cc/technologies/active-surveillance/), [Mammography & tomosynthesis](https://onco.cc/technologies/mammography/), [Ductal carcinoma in situ (DCIS)](https://onco.cc/terms/dcis/), [Overdiagnosis and false alarms](https://onco.cc/bottlenecks/b-overdiagnosis/))

## State of the art

- COMET is the first randomised evidence that low-risk DCIS can be monitored rather than operated on, at least in the short term; LORIS and LORD will add longer follow-up.
- Genomic assays and validated clinicopathological criteria let many women omit radiotherapy after lumpectomy.
- Hypofractionated and partial-breast radiotherapy shorten treatment for those who need it; low-dose tamoxifen cuts side effects.
- DCIS is the clearest example of the overdiagnosis problem in oncology and the test bed for risk-stratified de-escalation.

## Open problems

- Distinguishing DCIS that would progress from DCIS that would not; molecular classifiers, mammographic AI and the monitoring trials are the route.
- Long-term safety of active monitoring beyond two years; LORIS and LORD follow-up and the COMET ten-year endpoint will tell.
- Overtreatment by mastectomy remains common; shared decision aids and radiotherapy omission tools are the response.
- Preventing progression pharmacologically or with vaccines (HER2-directed DCIS vaccine trials) rather than surgically.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Ductal_carcinoma_in_situ
- NCI: ductal carcinoma in situ: https://www.cancer.gov/types/breast/breast-cancer-types/dcis
- COMET trial (JAMA 2024): https://doi.org/10.1001/jama.2024.26698
- SSO-ASTRO-ASCO margin guideline for DCIS (JCO 2016): https://doi.org/10.1200/JCO.2016.68.3573
- LORD trial (NCT02492607): https://clinicaltrials.gov/study/NCT02492607

## Connected records

- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Invasive breast carcinoma of no special type (invasive ductal carcinoma)](https://onco.cc/cancers/invasive-breast-carcinoma-no-special-type/), [Invasive cribriform carcinoma of the breast](https://onco.cc/cancers/invasive-cribriform-carcinoma-breast/), [Lobular carcinoma in situ (LCIS)](https://onco.cc/cancers/lobular-carcinoma-in-situ/), [Male breast cancer](https://onco.cc/cancers/male-breast-cancer/), [Paget disease of the nipple](https://onco.cc/cancers/paget-disease-of-the-nipple/), [Papillary carcinomas of the breast (encapsulated, solid and invasive papillary)](https://onco.cc/cancers/papillary-carcinoma-breast/), [Phyllodes tumour of the breast](https://onco.cc/cancers/phyllodes-tumour/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- technologies: [Active surveillance](https://onco.cc/technologies/active-surveillance/), [AI in radiology](https://onco.cc/technologies/radiology-ai-screening/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Mammography & tomosynthesis](https://onco.cc/technologies/mammography/), [MRI](https://onco.cc/technologies/mri/), [Sentinel lymph node biopsy](https://onco.cc/technologies/sentinel-node/)
- targets: [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/), [HER2](https://onco.cc/targets/her2/)
- drugs: [Anastrozole](https://onco.cc/drugs/anastrozole/), [MammaPrint (70-gene signature)](https://onco.cc/drugs/mammaprint/), [Oncotype DX](https://onco.cc/drugs/oncotype-dx/), [Tamoxifen](https://onco.cc/drugs/tamoxifen/)
- pathways: [Oestrogen receptor signalling](https://onco.cc/pathways/er-signaling/)
- terms: [Carcinoma in situ (CIS)](https://onco.cc/terms/carcinoma-in-situ/), [Ductal carcinoma in situ (DCIS)](https://onco.cc/terms/dcis/), [In situ](https://onco.cc/terms/in-situ/), [Lumpectomy (breast-conserving surgery)](https://onco.cc/terms/lumpectomy/), [Mastectomy](https://onco.cc/terms/mastectomy/)
- trials: [COMET (Comparison of Operative versus Monitoring and Endocrine Therapy)](https://onco.cc/trials/comet-dcis/), [NSABP B-39/RTOG 0413](https://onco.cc/trials/nsabp-b39/), [Radiation Therapy With or Without Trastuzumab in Treating Women With Ductal Carcinoma In Situ Who Have Undergone Lumpectomy](https://onco.cc/trials/nct00769379/), [TAM-01](https://onco.cc/trials/tam-01/)
- bottlenecks: [Overdiagnosis and false alarms](https://onco.cc/bottlenecks/b-overdiagnosis/), [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/)
- key papers: [Society of Surgical Oncology-American Society for Radiation Oncology-American Society of Clinical Oncology Consensus Guideline on Margins for Breast-Conserving Surgery With Whole-Breast Irradiation in Ductal Carcinoma In Situ](https://onco.cc/key-papers/paper-morrow-j-clin-oncol/)
- people: [Andrea DeCensi](https://onco.cc/people/andrea-decensi/), [E. Shelley Hwang](https://onco.cc/people/shelley-hwang/)
- journals: [Breast cancer](https://onco.cc/journals/breast-cancer-jbcs/), [Breast cancer research](https://onco.cc/journals/breast-cancer-research/), [Breast cancer research and treatment](https://onco.cc/journals/breast-cancer-research-and-treatment/), [Clinical breast cancer](https://onco.cc/journals/clinical-breast-cancer/), [Journal of breast imaging](https://onco.cc/journals/journal-of-breast-imaging/), [Journal of mammary gland biology and neoplasia](https://onco.cc/journals/journal-of-mammary-gland-biology-and-neoplasia/), [The Breast](https://onco.cc/journals/the-breast/), [The breast journal](https://onco.cc/journals/the-breast-journal/)

---
JSON: https://onco.cc/api/v1/entities/ductal-carcinoma-in-situ.json