Margins after Breast Conserving Surgery for Invasive Breast Cancer and DCIS

In 2013 the Society of Surgical Oncology (SSO) and American Society for Radiation Oncology (ASTRO):
- Convened a multidisciplinary expert panel to review the available evidence regarding margin width and Ipsilateral breast tumor recurrence (IBTR) in patients with invasive cancer having breast conservation therapy
Meta-analysis and secondary data from prospective and retrospective trials led them to conclude that:
- Positive margins (defined as ink on invasive cancer) is associated with:
  - At least a 2-fold increase in IBTR
- Among patients with negative margins:
  - A margin width of no ink on tumor represent the optimal margin width to minimize the risk of IBTR:
    - Notably the routine practice of obtaining wider negative margins than no ink on tumor is not indicated
- While younger age is associated with both:
  - Increased IBTR after breast-conserving therapy as well as increased local chest wall relapse after mastectomy:
    - There is no evidence that increased margin width (over no ink on tumor) nullifies this increased risk of IBTR in younger patients
In 2016, margin guidelines related to the treatment of non-invasive breast cancer (DCIS) in the setting of breast conservation therapy were developed by the SSO, ASTRO, and American Society of Clinical Oncology (ASCO) in a similar manner
- A consensus statement released by a multidisciplinary panel included the optimal margins for pure ductal carcinoma in situ (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 0.1 cm):
    - The multidisciplinary panel recommends a 2 mm margin:
      - As these lesions have similar rates of IBTR as pure DCIS
References
- Moran MS, Schnitt SJ, Giuliano AE, Harris JR, Khan SA, Horton J, et al. Society of Surgical Oncology-American Society for Radiation Oncology consensus guideline on margins for breast-conserving surgery with whole-breast irradiation in stages I and II invasive breast cancer. Int J Radiat Oncol Biol Phys. 2014;88(3):553-564.
- Morrow M, Van Zee KJ, Solin LJ, Houssami N, Chavez-MacGregor M. 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.