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Replication stress (RS) is a key trait of cancer cells, and a potential actionable target in cancer treatment. Accurate methods to measure RS in tumour samples are currently lacking. DNA fibre analysis has been used as a common technique to measure RS in cell lines. Here, we investigated DNA fibre analysis on fresh breast cancer specimens and correlated DNA replication kinetics to known RS markers and genomic alterations. Fresh, treatment‐naïve primary breast cancer samples (n = 74) were subjected to ex vivo DNA fibre analysis to measure DNA replication kinetics. Tumour cell proliferation was confirmed by EdU incorporation and cytokeratin AE1/AE3 (CK) staining. The RS markers phospho‐S33‐RPA and γH2AX and the RS‐inducing proto‐oncogenes Cyclin E1 and c‐Myc were analysed by immunohistochemistry. Copy number variations (CNVs) were assessed from genome‐wide single nucleotide polymorphism (SNP) arrays. We found that the majority of proliferating (EdU‐positive) cells in each sample were CK‐positive and therefore considered to be tumour cells. DNA fibre lengths varied largely in most tumour samples. The median DNA fibre length showed a significant inverse correlation with pRPA expression (r = −0.29, p = 0.033) but was not correlated with Cyclin E1 or c‐Myc expression and global CNVs in this study. Nuclear Cyclin E1 expression showed a positive correlation with pRPA levels (r = 0.481, p < 0.0001), while cytoplasmic Cyclin E1 expression exhibited an inverse association with pRPA expression (r = −0.353, p = 0.002) and a positive association with global CNVs (r = 0.318, p = 0.016). In conclusion, DNA fibre analysis performed with fresh primary breast cancer samples is feasible. Fibre lengths were associated with pRPA expression. Cyclin E1 expression was associated with pRPA and the percentage of CNVs. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland. [ABSTRACT FROM AUTHOR]

Purpose This study aimed to validate and update a model for predicting the risk of axillary lymph node (ALN) metastasis for assisting clinical decision-making. Methods We included breast cancer patients diagnosed at six Dutch hospitals between 2011 and 2015 to validate the original model which includes six variables: clinical tumor size, tumor grade, estrogen receptor status, lymph node longest axis, cortical thickness and hilum status as detected by ultrasonography. Subsequently, we updated the original model using generalized linear model (GLM) tree analysis and by adjusting its intercept and slope. The area under the receiver operator characteristic curve (AUC) and calibration curve were used to assess the original and updated models. Clinical usefulness of the model was evaluated by false-negative rates (FNRs) at different cut-off points for the predictive probability. Results Data from 1416 patients were analyzed. The AUC for the original model was 0.774. Patients were classified into four risk groups by GLM analysis, for which four updated models were created. The AUC for the updated models was 0.812. The calibration curves showed that the updated model predictions were better in agreement with actual observations than the original model predictions. FNRs of the updated models were lower than the preset 10% at all cut-off points when the predictive probability was less than 12.0%. Conclusions The original model showed good performance in the Dutch validation population. The updated models resulted in more accurate ALN metastasis prediction and could be useful preoperative tools in selecting low-risk patients for omission of axillary surgery. [ABSTRACT FROM AUTHOR]

Replication stress (RS) is a key trait of cancer cells, and a potential actionable target in cancer treatment. Accurate methods to measure RS in tumour samples are currently lacking. DNA fibre analysis has been used as a common technique to measure RS in cell lines. Here, we investigated DNA fibre analysis on fresh breast cancer specimens and correlated DNA replication kinetics to known RS markers and genomic alterations. Fresh, treatment-naïve primary breast cancer samples (n = 74) were subjected to ex vivo DNA fibre analysis to measure DNA replication kinetics. Tumour cell proliferation was confirmed by EdU incorporation and cytokeratin AE1/AE3 (CK) staining. The RS markers phospho-S33-RPA and γH2AX and the RS-inducing proto-oncogenes Cyclin E1 and c-Myc were analysed by immunohistochemistry. Copy number variations (CNVs) were assessed from genome-wide single nucleotide polymorphism (SNP) arrays. We found that the majority of proliferating (EdU-positive) cells in each sample were CK-positive and therefore considered to be tumour cells. DNA fibre lengths varied largely in most tumour samples. The median DNA fibre length showed a significant inverse correlation with pRPA expression (r = -0.29, p = 0.033) but was not correlated with Cyclin E1 or c-Myc expression and global CNVs in this study. Nuclear Cyclin E1 expression showed a positive correlation with pRPA levels (r = 0.481, p < 0.0001), while cytoplasmic Cyclin E1 expression exhibited an inverse association with pRPA expression (r = -0.353, p = 0.002) and a positive association with global CNVs (r = 0.318, p = 0.016). In conclusion, DNA fibre analysis performed with fresh primary breast cancer samples is feasible. Fibre lengths were associated with pRPA expression. Cyclin E1 expression was associated with pRPA and the percentage of CNVs. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland., (© 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.)