Margins in DCIS

The standard adequate margin for patients with DCIS treated with breast-conserving surgery followed by whole-breast radiation is:
- 2 mm
Negative margins:
- Halve the risk of ipsilateral breast tumor recurrence (IBTR) compared with positive margins (defined as ink on DCIS)
A 2 mm margin minimizes the risk of IBTR relative to narrower negative margin widths:
- However, larger margins (>2 mm) do not significantly decrease IBTR
In 2016, margin guidelines related to the treatment of non-invasive breast cancer (e.g., DCIS) in the setting of breast-conservation therapy:
- Were developed by the Society of Surgical Oncology, American Society for Radiation Oncology, and the American College of Surgeons in a similar manner
- A consensus statement released by a multidisciplinary panel included:
  - The optimal margins for:
    - Pure DCIS and mixed tumors (invasive and non-invasive components within the same tumor) in the setting of breast conservation
- Results from the meta-analysis showed:
  - That a 2 mm margin decreases the risk of IBTR in pure DCIS compared to closer negative margins
    - This differs from the previous margin recommendation for invasive cancer:
      - Which remains no ink on tumor:
        However, in the setting of mixed tumors (invasive cancer with a DCIS component):
        The recommendation for negative margins remains no ink on tumor, as patients with mixed disease are treated as invasive cancer and therefore receive systemic therapy more often than pure DCIS patients
  - In the setting of DCIS with micro-invasion (no focus of invasive disease larger than 1 mm):
    - The multidisciplinary panel recommends a 2 mm margin:
      - As these lesions have similar rates of IBTR as pure DCIS
Patients with positive margins after breast-conserving surgery:
- Should undergo re-excision
Patients for whom adequate surgical margins cannot be achieved with lumpectomy:
- Total mastectomy should be performed
Complete axillary lymph node dissection should not be performed:
- In the absence of evidence of invasive cancer or proven axillary metastatic disease in women with apparent pure DCIS
- However, a small proportion of patients with apparent pure DCIS will be found to have invasive cancer at the time of their definitive surgical procedure:
  - Therefore, a sentinel lymph node biopsy should be strongly considered if the patient with apparent pure DCIS is to be treated with mastectomy or with excision in an anatomic location compromising the performance of a future sentinel lymph node procedure
References
Morrow M, Van Zee KJ, Solin LJ, et al. 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. J Clin Oncol. 2016;34(33):4040-4046.
Breast cancer. National Comprehensive Cancer Network. 2018. https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf. Accessed September 9, 2018.