## 3 Results  
### Data Description  
Table 2 shows the patient and specimen characteristics in the slices and lumpectomy dataset. Both patient groups have a similar age. The American College of Radiology (ACR) score, which reflects the breast density (1 = lowest density, 4 = highest density), is higher in the slices dataset. The obtained data varies between the two datasets. First, the slices dataset contains more measurements because spectra were obtained from the entire slice whereas for the lumpectomy dataset up to four locations, reflecting multiple spectra, were marked. Second, a limited number of IC and DCIS was measured in the lumpectomy dataset because of the limited number of tumor-positive resection margins. Third, in the tissue slices dataset, we could make a distinction between 'pure' and'mixed' data based on the histopathological information obtained afterward as described in Section 2.2.1. For the lumpectomy dataset, this was not possible as locations were marked immediately after the measurements without any information on the spatial distribution of the tissue types on the surface.  
From the 52 patients, we measured, 11 patients required an extra operation after the initial procedure, and in two patients, the excised lump contained a positive margin but some extra tissue was excised during the initial operation, which prevented the need for an extra operation. In these 13 patients, the tumor-positive areas were marked with black pathology ink in four patients. In eight out of the nine other patients, the location of the positive margin was at the peripheral or nipple side, which we did not measure with the hyperspectral camera as explained in Section 2.2.2. Therefore, with the presented hyperspectral data acquisition method, we were able to image and mark the tumor positive margin in 4 out of 5 patients that required an extra operation according to the Dutch guidelines. The H & E sections of these four locations and an overview of the histopathological information corresponding to all 110 measured locations are shown in Figure 4. Most locations were measured on connective and adipose tissue and none of the malignant locations contained more than 80% malignant tissue.  
\begin{table}
\begin{tabular}{l c c} \hline \hline  & **Tissue Slices Dataset** & **Lumpectomy Specim Dataset** \\ \hline
**Patient and specimen characteristics** & & \\ Number of patient & 42 & 52 \\ Patient age (mean \(\pm\) std) & \(55.8\pm 10.9\) & \(57.7\pm 10.4\) \\ Patient ACR (mean \(\pm\) std) & \(2.81\pm 0.74\) & \(2.46\pm 0.80\) \\ Specim size (mean (range) & surface: 15 cm\({}^{2}\) (4–26) & volume: 51 cm\({}^{3}\) (6–240) \\  & thickness: 4.6 mm (2.5–8) & minimum thickness: 10 mm \\ Specimens surface flatness & As flat as possible & Spherical shaped \\ \hline
**Obtained data** & & \\ Tissue type measurements 1  & _spectra/\# patients_ & _locations/\# patients_ \\ _Invasive carcinoma_ & 6054/20 & 5/5 \\ _Ductal carcinoma in situ_ & 320/8 & 3/3 \\ _Connective_ & 1180/15 & 44 1/33 \\ _Adipose_ & 60,622/42 & 58 1/46 \\ Purity measurement & ‘pure’ and ‘mixed’ data & ’mixed’ data \\ Margin assessment & No & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 2: Data description of tissue slices and lumpectomy specimens.