Usefulness of 3D-surgical guides in breast conserving surgery after neoadjuvant treatment

We used 3D printed-breast surgical guides (3DP-BSG) to designate the original tumor area from the pre-treatment magnetic resonance imaging (MRI) during breast-conserving surgery (BCS) in breast cancer patients who received neoadjuvant systemic therapy (NST). Targeting the original tumor area in such patients using conventional localization techniques is difficult. For precise BCS, a method that marks the tumor area found on MRI directly to the breast is needed. In this prospective study, patients were enrolled for BCS after receiving NST. Partial resection was performed using a prone/supine MRI-based 3DP-BSG. Frozen biopsies were analyzed to confirm clear tumor margins. The tumor characteristics, pathologic results, resection margins, and the distance between the tumor and margin were analyzed. Thirty-nine patients were enrolled with 3DP-BSG for BCS. The median nearest distance between the tumor and the resection margin was 3.9 cm (range 1.2–7.8 cm). Frozen sections showed positive margins in 4/39 (10.3%) patients. Three had invasive cancers, and one had carcinoma in situ; all underwent additional resection. Final pathology revealed clear margins. After 3-year surveillance, 3/39 patients had recurrent breast cancer. With 3DP-BSG for BCS in breast cancer patients receiving NST, the original tumor area can be identified and marked directly on the breast, which is useful for surgery. Trial Registration: Clinical Research Information Service (CRIS) Identifier Number: KCT0002272. First registration number and date: No. 1 (27/04/2016).

Breast cancer is the most common malignant tumor found in women worldwide 1 . With the development of diagnostic breast imaging and the popularization of screening programs, the diagnosis of early breast cancer and the occurrence of breast-conserving surgery (BCS) have increased 2 . In early breast cancer, BCS has been established as a standard procedure due to the lack of prognostic difference between radiation therapy after partial excision and mastectomy 3 . As the breast is a cosmetically important organ in women, BCS should be attempted first, if possible. In cases where the tumor size is already large at the time of the discovery, a mastectomy may be necessary. In breast cancer, neoadjuvant systemic therapy (NST) is known to have a similar prognosis as adjuvant treatment 4 . However, in cases where the tumor size is too large for BCS at diagnosis, NST has been performed prior to attempting BCS 5 . Surgeons expected improved cosmetic results when performing BCS after NST due to decreased tissue removal, but a review disqualified this belief 6 . Positive margins at BCS are closely related to local recurrence, so adequate margins and total tumor excision are vital 7 . Precise tumor removal requires techniques that accurately identify and indicate the tumor area. Imaging techniques such as mammography (MMG), ultrasonography (USG), and magnetic resonance imaging (MRI) are commonly used to obtain information about tumors. Among these, MRI is known to be the most accurate in detecting the extent of residual cancer after NST 8,9 . Several localization methods have been used to remove tumors that are challenging to identify with breast palpation alone. The most commonly used method, the MMG-or USG-guided wire localization (WL), may be associated with complications such as vasovagal syncope and pneumothorax, leading www.nature.com/scientificreports/ to problems during surgery like migration, cutting, and loss 10 . In addition, this procedure makes quantification of the tumor difficult 10,11 . New localization methods such as radio-guided occult lesion localization (ROLL) and radioactive seed localization (RSL) have been developed due to the limitations of WL. These methods have been useful in the partial tumor resection in patients who underwent NST 12 . Several breast imaging and localization techniques have been used to perform BCS after NST, but local recurrence rates have been higher than those in patients who underwent surgery first 13 . This is due to the difficulty in identifying the original tumor area from pre-treatment MRIs, and in marking the area directly on the breast. To solve this problem, a supine MRI-based 3D printed-breast surgical guide (3DP-BSG) was developed. We report the findings from using 3DP-BSG for patients receiving BCS after NST. MRI acquisition and production of the surgical guide. A bilateral breast MRI was performed before and after NST using a 1.5-T MRI system (Magnetom Avanto, Siemens Healthineers) and a dedicated breast surface coil in the prone position. A supine MRI was included to obtain breast images in the surgical position. The original tumor area and breast were three-dimensionally modeled by combining MRI data obtained before and after treatment ( Fig. 1A-C). In addition, the 3D-shape and the safety excision margin were designed by combining the modeled image and the 3D-images that were constructed based on the MRI data. The prepared digital model was saved in a stereo-lithography file format before being exported to a 3D printer (Connex3 Object500; Stratasys Corporation, Rchovot, Israel) for the surgical guide creation (Fig. 1D). The 3DP-BSG was modeled to be 0.5 cm outside the tumor edges to ensure free margins. To ensure accurate display of the tumor range, the 3DP-BSG was modeled according to the following guidelines: (1) the model fits on the skin surface of the breast, (2) includes a hole at the nipple, and (3) has direction marks indicating Operation and pathologic assessments. After general anesthesia, the arm was superiorly positioned for axillary surgery, and the prepared 3DP-BSG was applied. The 3DP-BSG was placed on the breast with the bilateral nipples and suprasternal notch utilized as landmarks. The groove of the 3DP-BSG, modeled along the boundary of the tumor, was used to draw the tumor area over the breast skin. A blue dye was injected via the 3DP-BSG column into the breast to mark the tumor borders internally (Fig. 2). The breast tissue, abnormal or otherwise, was removed following the tumor border, as indicated by the blue dye. Ties of different lengths at the 3 o' clock and 12 o' clock positions of the removed breast tissue indicated the tumor orientation. Tissue from several sites of the surgical cavity was extracted for frozen biopsy to analyze for residual cancer. In the case of any tumor-positive results, re-excision was performed. The lack of breast tissue continuity was not considered to affect recurrence and was excluded from the evaluation of the resection margin 14 . The distance from the tumor edge to the resection margin was measured at the 3, 6, 9, and 12 o' clock positions. A sentinel node biopsy (SNB) was performed depending on the cancer type, and an axillary lymph node dissection (ALND) was performed according to the presence of node metastasis.

Methods
Ethical approval. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.  Table 2. In four cases, frozen biopsies of the resection margins were positive, three for invasive cancer, and one for carcinoma in situ. Re-excision was performed with final pathology, revealing that all margins were clean; thus, there was no conversion to mastectomy. The median size of the long axis of the tumor was 1.2 cm (range 0-4.5 cm), and the median size of the long axis of the removed breast tissue was 6.5 cm (range 4.5-13.0 cm). The median distance between the tumor and the resection margin was 3.9 cm (range 1.2-7.8 cm). The median operation time was 80 min in the SNB group and 101.5 min in the ALND group. A 3-year follow-up revealed that three patients had breast cancer recurrence.

Results
In contrast to the MMG-or USG-guided targeting methods, the 3DP-BSG can quantitatively indicate the extent of the tumor in the breast on MRI. The advantage of using this method is that an area of the breast from a past MRI can be summoned, and this area can be marked on the present breast. In the 3DP-BSG method, a guide which is made based on MRI is placed on the breast after the target patient is under general anesthesia, and the outline of the tumor is drawn on the skin according to the groove marked on the guide and the column of the guide, to target the tumor inside the breast. A blue dye is injected after passing through the syringe.

Discussion
Since breasts are cosmetically important to women, partial excision is attempted in patients with breast cancer, if possible. It is widely known that sexual and psychosocial outcomes are better in patients who undergo BCS than in those who undergo mastectomy 15 . When performing BCS, securing adequate margins for complete tumor removal while maximizing cosmetic results is necessary. These outcomes can be achieved by ensuring minimal breast deformity and asymmetry by preserving the maximal volume of normal breast tissue. NST can convert inoperable tumors into operable ones, provide early information on tumor response to treatment, and reduce the administration of chemotherapy in the absence of treatment response 16 . In large tumors, NST is performed for size reduction in an attempt to preserve the breast. According to previous literature, however, the occurrence rate of tumor-positive resection margins in BCS after NST is 40% 6 . According to a report by the Early Breast Cancer Trialists' Collaborative Group (EBCTCG), the local recurrence rate was higher in patients who received BCS after NST than in those who received adjuvant therapy after BCS 13

Multifocality (pathologic)
Yes 5 (12. www.nature.com/scientificreports/   www.nature.com/scientificreports/ patients were free of macroscopic residual tumor 23 . The simplest method is to insert a radiopaque clip into the tumor margin before treatment. However, the disadvantages with this technique include placement difficulty, migration, loss, failure, and patient pain. Success also depends on the type of tissue marker clips used, since metallic clips can cause artifacts and reduce MRI sensitivity 24  Theoretically, when using 3DP-BSG, the tumor should be completely and precisely removed. In our study, 10.3% of the patients had positive margins. This was likely due to the tumor actual size being larger than that observed on MRI, due to MRI limitations. Additionally, our study showed a 7.7% recurrence rate after a 3-year follow-up. A meta-analysis of ten randomized trials performed with BCS after NST 13 reported a 5-year local recurrence rate of 12.1%. Although the follow-up period was short in our study, the obtained results were promising. Compared to other conventional localization techniques, 3DP-BSG has many advantages. First, the tumor area noted on the MRI can be marked both within the breast and on the skin. Second, in patients receiving NST, the area of the original tumor before treatment can be marked. Third, BSG is a localization technique that does not cause pain in the patient. Fourth, since the 3DP-BSG is made prior to surgery, it does not require changes in the surgery schedule or increased preparation time for localization. Fifth, there is no risk of radiation exposure. Sixth, there is no risk of migration, loss, or cutting. In addition, the use of a 3DP-BSG allows for the preservation of normal breast tissue and precise tumor removal, enhancing the cosmetic effect. We expect that even beginners can easily overcome the BCS learning curve.
In conclusion, utilizing 3DP-BSGs in patients undergoing BCS after NST revealed a low rate of tumor-positive margins. By using 3DP-BSG as a localization method in patients receiving NST, it is possible to precisely target the original tumor area observed in the pre-treatment MRI. In addition, the advantages of the method are that it is painless, does not include radiation, and does not increase the procedure time.