# Ductal Carcinoma In Situ (DCIS) and High-Risk Lesions

## Ductal Carcinoma In Situ (DCIS)

### Overview

Ductal carcinoma in situ is a non-invasive breast cancer in which malignant epithelial cells are confined within the basement membrane of the duct. It comprises 20-25% of screen-detected breast cancers. The natural history is variable, with 15-50% of untreated DCIS progressing to invasive cancer over 10-20 years. While DCIS is considered an obligate precursor to invasive ductal carcinoma, many cases never progress.

### Presentation

DCIS is most commonly detected as microcalcifications on screening mammography. Less common presentations include a palpable mass, bloody nipple discharge, and Paget's disease of the nipple. Paget's disease presents as eczematous changes of the nipple and areola and is associated with underlying DCIS or invasive cancer in more than 90% of cases.

### Classification

DCIS is classified by nuclear grade (low, intermediate, or high) and architecture (comedo, cribriform, micropapillary, solid, or papillary). Comedo necrosis, characterized by central necrosis within ducts, is associated with high-grade DCIS and higher recurrence rates. Approximately 60-70% of DCIS is ER-positive.

### Surgical Management

#### Breast-Conserving Surgery (Lumpectomy) + Radiation

BCS with radiation is the standard treatment for most DCIS. The consensus margin standard is 2 mm, as established by the 2016 SSO-ASTRO-ASCO guideline. Margins of 2 mm reduce local recurrence compared to smaller margins, while wider margins beyond 2 mm do not provide further benefit. Whole-breast radiation therapy reduces ipsilateral recurrence by approximately 50%, as demonstrated by the NSABP B-17 and EORTC 10853 trials. Notably, half of all local recurrences after DCIS treatment are invasive cancer.

#### Lumpectomy Alone (Without Radiation)

Lumpectomy without radiation may be considered for low-risk DCIS with wide margins. Risk stratification identifies low-risk features as small size (less than 2.5 cm), low or intermediate grade, negative margins greater than 3 mm, and screen-detected lesions. The Van Nuys Prognostic Index scores patients based on size, margin width, grade, and age; a VNPI score of 4-6 indicates low recurrence risk where excision alone may be adequate. Patients must accept a higher local recurrence risk of 15-20% at 10 years compared to 5-10% with radiation. The COMET (Comparison of Operative to Monitoring and Endocrine Therapy) and LORD (Low-Risk DCIS) trials are ongoing and investigating active surveillance for low-risk DCIS.

#### Mastectomy

Mastectomy is indicated for multicentric DCIS, a large area of DCIS relative to breast size, inability to achieve 2 mm margins, or patient preference. It is curative, with a local recurrence rate of less than 1-2%. Sentinel lymph node biopsy should be performed when mastectomy is planned because occult invasive cancer is found in 10-20% of mastectomy specimens.

#### SLNB in DCIS

Sentinel lymph node biopsy is not routinely recommended for DCIS treated with BCS, as the risk of occult invasion is low and SLNB can still be performed if invasive cancer is found on final pathology. SLNB should be performed when mastectomy is planned (because it cannot be done after mastectomy), for large or palpable DCIS (which carries a higher risk of occult invasion), and for high-grade DCIS with a mass.

<image>Mammographic appearance of DCIS showing clustered pleomorphic microcalcifications in a segmental distribution with corresponding histologic image of high-grade comedo DCIS</image>

### Adjuvant Endocrine Therapy for DCIS

Tamoxifen (for premenopausal women) or an aromatase inhibitor (for postmenopausal women) is offered for ER-positive DCIS. The NSABP B-24 trial showed that tamoxifen reduced ipsilateral invasive recurrence and contralateral breast cancer. The NSABP B-35 trial demonstrated that anastrozole was superior to tamoxifen in postmenopausal women for the breast cancer-free interval. The benefits are modest, and the risks versus benefits should be discussed with the patient, including venous thromboembolism and endometrial cancer risk with tamoxifen, and musculoskeletal symptoms with aromatase inhibitors.

### Active Surveillance for DCIS

Active surveillance for low-risk DCIS is an emerging concept being investigated in the COMET and LORD trials. It is based on the recognition that many cases of low-grade DCIS never progress to invasive cancer. The approach involves mammographic monitoring without surgical treatment. This is not yet standard of care and should only be offered within clinical trials.

## High-Risk Breast Lesions

| High-Risk Lesion | Upgrade Rate on Excision | Cancer Risk | Management |
|-----------------|-------------------------|-------------|------------|
| ADH | 15–30% | 4–5× bilateral | Excision recommended |
| Classic LCIS | Low (risk marker) | 7–12× bilateral | Surveillance ± risk reduction |
| Pleomorphic LCIS | Higher | Similar to DCIS | Excision (manage like DCIS) |
| ALH | 5–10% | Part of lobular neoplasia spectrum | Excision if discordant |
| FEA | 5–10% | Low | Excision if associated with other atypia |
| Papilloma without atypia | 5–10% | Low | Excision recommended |
| Papilloma with atypia | 15–30% | Moderate | Excision mandatory |

### Atypical Ductal Hyperplasia (ADH)

Atypical ductal hyperplasia is a proliferative lesion with some but not all features of DCIS. When found on core needle biopsy, it upgrades to DCIS or invasive cancer on excision in 15-30% of cases. Surgical excision is recommended for all ADH found on CNB. Long-term, ADH confers a 4-5 times increased risk of developing breast cancer bilaterally. Tamoxifen or raloxifene reduces this risk by approximately 50%.

### Lobular Neoplasia

#### Lobular Carcinoma In Situ (LCIS)

LCIS is a proliferation of dyshesive cells that fill and expand the lobules. It is a risk factor for future breast cancer, conferring a 7-12 times increased bilateral risk. Importantly, it is not an obligate precursor but rather a risk marker. It is typically an incidental finding and is usually not associated with calcifications. Classic LCIS found on CNB may be observed if concordant with imaging, though surgical excision is recommended if discordant. Pleomorphic LCIS behaves more like DCIS, and excision is recommended with potential need for radiation. Long-term management includes enhanced screening with annual mammography plus MRI if the lifetime risk exceeds 20%. Risk reduction options include tamoxifen or raloxifene and, for very high-risk patients, bilateral prophylactic mastectomy.

#### Atypical Lobular Hyperplasia (ALH)

Atypical lobular hyperplasia is part of the lobular neoplasia spectrum but involves fewer cells than LCIS. The upgrade rate on excision is 5-10%. Management is similar to LCIS: excision if discordant with imaging, and observation if concordant and small.

### Flat Epithelial Atypia (FEA)

Flat epithelial atypia is columnar cell change with low-grade cytologic atypia, often found with microcalcifications on mammography. The upgrade rate on excision is 5-10%, usually to ADH or DCIS. Management is controversial; excision is recommended when associated with other atypia, while observation may be appropriate for isolated FEA that is concordant with imaging.

### Papillary Lesions

Intraductal papilloma is a benign lesion, typically central or subareolar, that presents with nipple discharge. Solitary papilloma without atypia has an upgrade rate of 5-10% and excision is recommended. Papilloma with atypia has an upgrade rate of 15-30% and excision is mandatory. Papillary carcinoma involves DCIS or invasive cancer arising within papillary architecture and is managed as breast cancer.

### Radial Scar (Complex Sclerosing Lesion)

Radial scar is a spiculated lesion on imaging that mimics carcinoma. Radiologic-pathologic discordance is common, as imaging cannot reliably distinguish it from cancer. Excision is recommended if the lesion is larger than 1 cm, associated with atypia, or discordant with imaging and pathology findings. Small radial scars without atypia found on vacuum-assisted biopsy may be appropriate for observation.

### Phyllodes Tumor

Phyllodes tumor is a fibroepithelial neoplasm that presents as a rapidly growing mass and is classified as benign, borderline, or malignant. Benign tumors are treated with wide local excision with 1 cm margins or enucleation if margins are achievable. Borderline and malignant tumors require wide local excision with a minimum of 1 cm margins, or mastectomy if margins cannot be achieved. Axillary surgery is not indicated because phyllodes tumors metastasize hematogenously rather than via lymphatics. Recurrence rates are 10-15% for benign, 20-25% for borderline, and 25-40% for malignant tumors. Malignant phyllodes may benefit from adjuvant radiation, though evidence is limited.

<image>Histologic comparison of normal breast ductal epithelium, atypical ductal hyperplasia (ADH), low-grade DCIS, and high-grade DCIS showing the progression of cellular atypia and architectural changes</image>

## Risk Reduction Strategies for High-Risk Patients

### Chemoprevention

Tamoxifen reduces breast cancer risk by 49% in high-risk women, as demonstrated by the NSABP P-1 trial. It is appropriate for both pre- and postmenopausal women, though side effects include venous thromboembolism, endometrial cancer, and hot flashes. Raloxifene provides similar risk reduction with fewer side effects but is limited to postmenopausal women, as shown in the STAR trial. Aromatase inhibitors, including exemestane (MAP.3 trial) and anastrozole (IBIS-II trial), demonstrate 50-65% risk reduction in postmenopausal women and are seeing increasing adoption as preferred agents in this population.

### Prophylactic Surgery

Bilateral prophylactic mastectomy reduces breast cancer risk by more than 95% and is primarily considered for BRCA1/2 carriers, those with strong family history, and Li-Fraumeni syndrome patients. This is a patient-driven decision after extensive counseling. Risk-reducing bilateral salpingo-oophorectomy reduces breast cancer risk by approximately 50% in BRCA carriers when performed before menopause and also reduces ovarian cancer risk. It is recommended at age 35-40 for BRCA1 carriers and 40-45 for BRCA2 carriers, after childbearing is complete.

### Enhanced Surveillance

Enhanced surveillance consists of annual mammography plus breast MRI, staggered at 6-month intervals, along with clinical breast examination every 6-12 months. This is recommended for BRCA carriers, Li-Fraumeni syndrome patients, prior chest radiation recipients, and other high-risk syndromes.

<image>Algorithm for management of high-risk breast lesions found on core needle biopsy showing decision pathways for ADH, LCIS, ALH, FEA, papillary lesions, and radial scars</image>

## Clinical Pearls

DCIS margins should be at least 2 mm, which is the consensus standard and differs from the "no ink on tumor" standard used for invasive cancer. SLNB should be performed with mastectomy for DCIS because occult invasion is found in 10-20% of specimens and SLNB cannot be done after mastectomy. Classic LCIS is a risk marker, not an obligate precursor, and confers bilateral risk; management focuses on surveillance and risk reduction rather than necessarily requiring excision. Pleomorphic LCIS behaves more aggressively and should be managed like DCIS with excision, margin assessment, and consideration of radiation. ADH on CNB has a 15-30% upgrade rate on excision, making surgical excision mandatory. Active surveillance for low-risk DCIS is being studied in the COMET and LORD trials but is not standard of care and should not be offered outside a clinical trial. Risk-reducing medications such as tamoxifen and aromatase inhibitors are underutilized and should be considered for all patients with high-risk lesions or elevated lifetime risk.

## References
- Morrow M, et al. SSO-ASTRO-ASCO consensus guideline on margins for breast-conserving surgery with whole-breast irradiation in ductal carcinoma in situ. Ann Surg Oncol. 2016;23(12):3801-3810.
- Wapnir IL, et al. Long-term outcomes of invasive ipsilateral breast tumor recurrences after lumpectomy in NSABP B-17 and B-24 randomized clinical trials for DCIS. J Natl Cancer Inst. 2011;103(6):478-488.
- King TA, et al. Lobular carcinoma in situ: A 29-year longitudinal experience evaluating clinicopathologic features and breast cancer risk. J Clin Oncol. 2015;33(33):3945-3952.
- Fisher B, et al. Tamoxifen for the prevention of breast cancer: Current status of the National Surgical Adjuvant Breast and Bowel Project P-1 study. J Natl Cancer Inst. 2005;97(22):1652-1662.
- Cuzick J, et al. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II). Lancet. 2014;383(9922):1041-1048.