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Ductal carcinoma in situ (DCIS) is a non-invasive breast cancer that can progress into invasive ductal carcinoma (IDC). Studies suggest DCIS is often overtreated since a considerable part of DCIS lesions may never progress into IDC. Lower grade lesions have a lower progression speed and risk, possibly allowing treatment de-escalation. However, studies show significant inter-observer variation in DCIS grading. Automated image analysis may provide an objective solution to address high subjectivity of DCIS grading by pathologists. In this study, we developed and evaluated a deep learning-based DCIS grading system. The system was developed using the consensus DCIS grade of three expert observers on a dataset of 1186 DCIS lesions from 59 patients. The inter-observer agreement, measured by quadratic weighted Cohen's kappa, was used to evaluate the system and compare its performance to that of expert observers. We present an analysis of the lesion-level and patient-level inter-observer agreement on an independent test set of 1001 lesions from 50 patients. The deep learning system (dl) achieved on average slightly higher inter-observer agreement to the three observers (o1, o2 and o3) (κo1,dl= 0.81, κo2,dl= 0.53 and κo3,dl= 0.40) than the observers amongst each other (κo1,o2= 0.58, κo1,o3= 0.50 and κo2,o3= 0.42) at the lesion-level. At the patient-level, the deep learning system achieved similar agreement to the observers (κo1,dl= 0.77, κo2,dl= 0.75 and κo3,dl= 0.70) as the observers amongst each other (κo1,o2= 0.77, κo1,o3= 0.75 and κo2,o3= 0.72). The deep learning system better reflected the grading spectrum of DCIS than two of the observers. In conclusion, we developed a deep learning-based DCIS grading system that achieved a performance similar to expert observers. To the best of our knowledge, this is the first automated system for the grading of DCIS that could assist pathologists by providing robust and reproducible second opinions on DCIS grade.

Histologic grade is a biomarker that is widely used to guide treatment of invasive breast cancer (IBC) and ductal carcinoma in situ of the breast (DCIS). Yet, currently, substantial grading variation between laboratories and pathologists exists in daily pathology practice. This study was conducted to evaluate whether an e-learning may be a feasible tool to decrease grading variation of (pre)malignant breast lesions. An e-learning module, representing the key-concepts of grading (pre)malignant breast lesions through gold standard digital images, was designed. Pathologists and residents could take part in either or both the separate modules on DCIS and IBC. Variation in grading of a digital set of lesions before and after the e-learning was compared in a fully-crossed study-design. Multiple outcome measures were assessed: inter-rater reliability (IRR) by Light's kappa, the number of images graded unanimously, the number of images with both extreme scores (i.e., grade I and grade III), and the average number of discrepancies from expert-consensus. Participants were included as they completed both the pre- and post-e-learning set (DCIS-module: n= 36, IBC-module: n= 21). For DCIS, all outcome measures improved after e-learning, with the IRR improving from fair (kappa: 0.532) to good (kappa: 0.657). For IBC, all outcome measures for the subcategories tubular differentiation and mitosis improved, with >90% of participants agreeing on almost 90% of the images after the e-learning. In contrast, the IRR for the subcategory of nuclear pleomorphism remained fair (kappa: 0.523 vs. kappa: 0.571). This study shows that an e-learning module, in which pathologists and residents are trained in histologic grading of DCIS and IBC, is a feasible and promising tool to decrease grading variation of (pre)malignant breast lesions. This is highly relevant given the important role of histologic grading in clinical decision making of (pre)malignant breast lesions.

Histologic grade is a biomarker that is widely used to guide treatment of invasive breast cancer (IBC) and ductal carcinoma in situ of the breast (DCIS). Yet, currently, substantial grading variation between laboratories and pathologists exists in daily pathology practice. This study was conducted to evaluate whether an e-learning may be a feasible tool to decrease grading variation of (pre)malignant breast lesions. An e-learning module, representing the key-concepts of grading (pre)malignant breast lesions through gold standard digital images, was designed. Pathologists and residents could take part in either or both the separate modules on DCIS and IBC. Variation in grading of a digital set of lesions before and after the e-learning was compared in a fully-crossed study-design. Multiple outcome measures were assessed: inter-rater reliability (IRR) by Light’s kappa, the number of images graded unanimously, the number of images with both extreme scores (i.e., grade I and grade III), and the average number of discrepancies from expert-consensus. Participants were included as they completed both the pre- and post-e-learning set (DCIS-module: n= 36, IBC-module: n= 21). For DCIS, all outcome measures improved after e-learning, with the IRR improving from fair (kappa: 0.532) to good (kappa: 0.657). For IBC, all outcome measures for the subcategories tubular differentiation and mitosis improved, with >90% of participants agreeing on almost 90% of the images after the e-learning. In contrast, the IRR for the subcategory of nuclear pleomorphism remained fair (kappa: 0.523 vs. kappa: 0.571). This study shows that an e-learning module, in which pathologists and residents are trained in histologic grading of DCIS and IBC, is a feasible and promising tool to decrease grading variation of (pre)malignant breast lesions. This is highly relevant given the important role of histologic grading in clinical decision making of (pre)malignant breast lesions.

Distant breast cancer metastases are nowadays routinely biopsied to reassess receptor status and to isolate DNA for sequencing of druggable targets. Bone metastases are the most frequent subgroup. Decalcification procedures may negatively affect antigenicity and DNA quality. We therefore evaluated the effect of several decalcification procedures on receptor status and DNA/RNA quality. In 23 prospectively collected breast tumors, we compared ERα, PR and HER2 status by immunohistochemistry in (non-decalcified) tissue routinely processed for diagnostic purposes and in parallel tissue decalcified in Christensen’s buffer with and without microwave, EDTA and Formical-4. Furthermore, HER2 fluorescence in situ hybridization and DNA/RNA quantity and quality were assessed. We found that the percentage of ERα-positive cells were on average lower in EDTA (P=0.049) and Formical-4 (P=0.047) treated cases, compared with controls, and PR expression showed decreased antigenicity after Christensen’s buffer treatment (P=0.041). Overall, a good concordance (weighted kappa) was seen for ERα, PR and HER2 immunohistochemistry when comparing the non-decalcified control tissues with the decalcified tissues. For two patients (9%), there was a potential influence on therapeutic decision making with regard to hormonal therapy or HER2-targeted therapy. HER2 fluorescence in situ hybridization interpretation was seriously hampered by Christensen’s buffer and Formical-4, and DNA/RNA quantity and quality were decreased after all four decalcification procedures. Validation on paired primary breast tumor specimens and EDTA-treated bone metastases showed that immunohistochemistry and fluorescence in situ hybridization were well assessable and DNA and RNA yield and quality were sufficient. With this, we conclude that common decalcification procedures have only a modest negative influence on hormone and HER2 receptor immunohistochemistry in breast cancer. However, they may seriously affect DNA/RNA-based diagnostic procedures. Overall, EDTA-based decalcification is therefore to be preferred as it best allows fluorescence in situ hybridization and DNA/RNA isolation.

Distant breast cancer metastases are nowadays routinely biopsied to reassess receptor status and to isolate DNA for sequencing of druggable targets. Bone metastases are the most frequent subgroup. Decalcification procedures may negatively affect antigenicity and DNA quality. We therefore evaluated the effect of several decalcification procedures on receptor status and DNA/RNA quality. In 23 prospectively collected breast tumors, we compared ERα, PR and HER2 status by immunohistochemistry in (non-decalcified) tissue routinely processed for diagnostic purposes and in parallel tissue decalcified in Christensen's buffer with and without microwave, EDTA and Formical-4. Furthermore, HER2 fluorescence in situhybridization and DNA/RNA quantity and quality were assessed. We found that the percentage of ERα-positive cells were on average lower in EDTA (P=0.049) and Formical-4 (P=0.047) treated cases, compared with controls, and PR expression showed decreased antigenicity after Christensen's buffer treatment (P=0.041). Overall, a good concordance (weighted kappa) was seen for ERα, PR and HER2 immunohistochemistry when comparing the non-decalcified control tissues with the decalcified tissues. For two patients (9%), there was a potential influence on therapeutic decision making with regard to hormonal therapy or HER2-targeted therapy. HER2 fluorescence in situhybridization interpretation was seriously hampered by Christensen's buffer and Formical-4, and DNA/RNA quantity and quality were decreased after all four decalcification procedures. Validation on paired primary breast tumor specimens and EDTA-treated bone metastases showed that immunohistochemistry and fluorescence in situhybridization were well assessable and DNA and RNA yield and quality were sufficient. With this, we conclude that common decalcification procedures have only a modest negative influence on hormone and HER2 receptor immunohistochemistry in breast cancer. However, they may seriously affect DNA/RNA-based diagnostic procedures. Overall, EDTA-based decalcification is therefore to be preferred as it best allows fluorescence in situhybridization and DNA/RNA isolation.