Breast cancer is the most common malignancy among women in the United States (US). According to the American Cancer Society, the incidence of invasive and noninvasive breast cancer in the US for 2025 was approximately 316  950 and 59 080, respectively.1 Treatment of breast cancer varies, ranging from lumpectomy to mastectomy, often combined with customized oncoplastic approaches and reconstructive procedures.2

Breast-conserving surgery (BCS) followed by whole-breast radiation, which aims to excise the tumor and obtain completely negative resection margins, has been widely adopted because it provides the same prognosis as mastectomy while maximally preserving the cosmetic appearance of the breast.3 However, local cancer recurrence remains a key challenge for surgeons and oncologists, frequently necessitating additional surgery. One of the strongest predictors of local recurrence is the presence of positive surgical margins4, which often necessitates a second surgery.5–7 These subsequent surgeries for re-excision are associated with an added financial burden, increased potential for patient morbidity, greater patient anxiety, and worse cosmesis.8, 9

Cavity shave margin (CSM) is a technique that involves the resection of the additional margins from the tumor bed after primary tumor excision. The additional margins are then labeled, oriented, and inked at the pathology laboratory. The pathologist then assesses these margins as the new final margins and renders a final pathological diagnosis based on them.

The Society of Surgical Oncology (SSO) and the American Society for Radiation Oncology (ASTRO) have recommended the following definition of negative surgical margin: no tumor on the inked margin in case of invasive cancer10 and no tumor at least 2 mm from the inked surface for ductal carcinoma in situ (DCIS).11

Several studies have demonstrated that CSM is a potentially effective method for reducing positive margins and re-excision rates without compromising aesthetic outcomes7, 12, 13 Despite these findings, barriers to its routine adoption include the lack of consensus on the definition of an acceptable negative margin and the variation in cavity shaving volume between different surgeons14–16, as well as a lack of standardized protocol among institutions and the preferences of the treating surgeons.

In this single-institution study, we aimed to compare the effect of performing the CSM procedure in conjunction with BCS on the final margin status and re-excision rates in patients with invasive ductal carcinoma (IDC) and/or DCIS with that of BCS without CSM. This topic warrants prompt attention, as it directly impacts patient outcomes and informs the selection of an appropriate treatment approach.

We conducted a single-institution retrospective study comprising 529 women with a biopsy-proven diagnosis of IDC and/or DCIS who underwent either partial mastectomy with CSM or without CSM between January 1, 2013, and December 31, 2015, at Detroit Medical Center. Data analysis was performed in 2022. Exclusion criteria included (1) male sex; (2) age younger than 18 years; (3) tumor other than IDC and DCIS histology (such as lobular carcinoma in situ, invasive lobular carcinoma, neuroendocrine carcinoma, and other rare tumors); (4) presence of residual and/or recurrent disease; (5) history of prior surgical excision such as excisional biopsies or partial mastectomy; (6) prior neoadjuvant chemotherapy; and (7) patients who underwent oncoplastic techniques.

We classified cases as “with CSM” if the patient received cavity shave excision of all 6 margin faces (superior, inferior, lateral, medial, anterior, and posterior) and “without CSM” if the patient underwent primary excision without additional shave margins. Three surgeons participated in the study. In accordance with the surgeon’s practice, neither partial cavity shave procedures (shave excision of ≥ 1 but < 6 margin faces) nor intraoperative frozen section analysis was performed. Patients with a high risk for lymph node (LN) disease, including those with high-grade IDC, DCIS, or clinical and radiological indications of axillary disease, also underwent axillary LN dissection. We obtained postprocedure margin status as a pathological end point for both IDC and DCIS with reference to 2 definitions: (1) positive margin: tumor on the inked margin for IDC; and (2) positive close margin: tumor within 2 mm of the inked margin for both IDC and DCIS. At our institution, close margins were generally managed as follows: for cases with pure DCIS, a re-excision was performed when the DCIS was 2 mm or less from the inked margin. In contrast, for cases with both invasive and in situ components, positive close margins for DCIS and/or IDC did not prompt re-excision, provided the inked margins were negative for either component. For IDC, re-excision was performed only when IDC was present on the inked margin.

The decision to re-excise, representing the clinical decision-making outcome, was left to the discretion of the treating surgeon and was independent of patient or tumor characteristics.

We collected data regarding the patients’ age and tumor characteristics, including (1) DCIS status, grade, size, and margin status (tumor on the ink and within 2 mm of the inked margin); (2) IDC status, grade (based on established criteria for tubule formation, nuclear pleomorphism, and mitotic count according to the Nottingham Grading System22), size, focality (unifocal or multifocal), and margin status (tumor on the ink and within 2 mm of the inked margin); (3) type of LN excised: sentinel LN or axillary LN; (4) size of metastases to LN: macrometastases (> 2 mm), micrometastases (> 0.2 to ≤ 2.0 mm), and isolated tumor cells (ITCs) (≤ 0.2 mm or 200 cells)19; and (5) type of surgical procedure performed: BCS with or without CSM.

We first stratified the data into 2 groups based on the surgical procedure performed (BCS with CSM or standard BCS). We further subdivided these groups into 3 categories based on invasive and/or in situ disease: patients with only DCIS, patients with only IDC, and patients with both IDC and DCIS.

This study aimed to evaluate whether excision of additional margins from the tumor bed at the time of primary surgery reduces the incidence of positive surgical margins (both inked margin and close margin) and the need for re-excision, compared with BCS without CSM across 3 groups: patients with only DCIS, patients with only IDC, and patients with mixed IDC and DCIS.

In our study, re-excision was left to the surgeon’s discretion, which represents an important source of potential bias that should be considered when interpreting our results. Our study failed to establish the superiority of the CSM technique over the standard surgical technique (without CSM) in reducing the incidence of positive margins (both inked margins and close margins). However, our study revealed that patients in the CSM group had lower rates of re-excision, particularly those with pure IDC. We also observed a strong association between re-excision and positive margins (both inked and close margins) in both surgical groups. Among patients in the CSM group (Table S1), re-excision was significantly more likely when a tumor was present on the inked margin (53.8% vs 6.6%) or within 2 mm of the inked margin (Table S2; 75.6% vs 41.5%; P < 0.001 for both). Similarly, in patients in the non-CSM group, re-excision was significantly more likely when a tumor was present on the inked margin (Table S3; 71.4% vs 6.8%) or within 2 mm of the inked margin (Table S4; 92.9% vs 46.6%; P < 0.001 and P = 0.001, respectively).

Many previously published studies17-19 have consistently documented the beneficial effect of the CSM procedure in reducing the rate of positive margins compared with those without CSM. The heterogeneity in defining positive and close margins across previous studies may explain the nonsignificant effect of the CSM procedure in reducing positive margins observed in our results. These inconsistent definitions complicate direct comparisons. In our study, “CSM” was defined as the shaving of all 6 cavity margins. We applied stringent margin criteria for both invasive (IDC) and in situ (DCIS) components, ensuring a rigorous and systematic approach. In a randomized controlled trial, Chagpar et al.17 reported a significant reduction in the incidence of positive margins from 34% to 19%. However, in this study, the authors defined close margins as those in which the tumor is present within 1 mm of the edge of the specimen.17 In another study, Corsi et al.20 compared standard BCS with BCS combined with the CSM procedure. They found that patients in the CSM group had significantly increased rates of cancers with negative margins (98.3% vs 74.4%) and decreased rates of re-excision (1.9% vs 18.9%). However, here the authors did not include close margins in their analysis.

The existing literature has also demonstrated a strong association between positive margins and tumor clinicopathological properties, such as tumor size (including both invasive and DCIS components)21, presence of a DCIS component22, DCIS size23, and axillary LN status, on both univariable and multivariable analyses.21 In 2023, Fauveau et al.23 found that large-sized DCIS was independently associated with a higher rate of positive margins after standard BCS. Similar to the aforementioned studies, our study showed that patients with a larger DCIS size (Table S3) had a higher risk of having a tumor on the margin (OR, 1.18; 95% CI, 1.10–1.27; P < 0.001) and tumor within 2 mm of the margin (OR, 1.21; 95% CI, 1.12–1.32; P < 0.001) compared with those with a smaller DCIS size. In our study, patients with only IDC had a decreased risk of having a tumor on the margin compared with those with only DCIS, suggesting that the presence of a DCIS component is a high-risk factor for positive margins, regardless of the procedure used.

Our study revealed that patients in the CSM group had lower rates of re-excision, particularly those with pure IDC. The beneficial effect of the CSM procedure in decreasing re-excision rates observed in our study aligns with many previous studies17–19, which reported that performing CSM with primary surgery results in a marked reduction in the need for a second surgery by more than 50%. Although only 50% of patients with a tumor on the inked margin in the CSM group required re-excision due to positive inked margins, compared with 68.9% (n = 42) in the non-CSM group, the difference was minimal (P = 0.18). However, we observed a statistically significant difference among patients with positive close margins in both groups, with patients in the CSM group having a lower risk of re-excision compared with those in the non-CSM group (15.9% vs 33%; P = 0.004), particularly in cases of only DCIS.

Our study has several limitations. First, the study focused on DCIS and IDC histological types of breast cancer and has not taken into consideration other common breast cancer types, such as lobular carcinoma in situ and invasive lobular carcinoma. Exclusion of in situ and invasive lobular cancer was based on the previously established data which established that pure lobular carcinoma is associated with increased margin positivity rates compared with IDC (8.63% vs 4.55%; P < 0.001)7; this limits the application of our findings to lobular carcinoma of the breast, which may have different clinical characteristics and outcomes. Second, variations in surgeons’ practices in surgical technique selection and lack of standardized re-excision criteria might have introduced bias in the study. Third, we did not assess the effect of radiotherapy on the risk of re-excision in patients in either surgical group. Fourth, the retrospective nature of the study, missing data for a few cases, and lack of data on cost and resource utilization may have limited the analysis. Fifth, lack of information on prior surgical excisions and residual or recurrent disease, and the influence of preoperative tumor- or patient-related factors on the choice of surgical technique may introduce selection bias. Sixth, a cohort from a single institution might introduce selection bias and reduce generalizability. Additionally, the study is limited by the lack of information on molecular profiles of the tumor and lymphovascular invasion, which are important prognostic factors in breast cancer. Finally, we did not consider the patient perspectives or report cosmetic outcomes comparing cavity shave margins without CSM.

BCS with the CSM procedure offers minimal benefit in reducing the incidence of positive margins compared with BCS alone in patients diagnosed with pure IDC, pure DCIS, and/or mixed invasive and in situ cancer. However, future large-scale studies with standardized margin guidelines and re-excision criteria, and assessment of tumor molecular profile and lymphovascular invasion are recommended to better guide clinical decision-making.