HER2-low and tumor infiltrating lymphocytes in triple-negative breast cancer: Are they connected?

Most patients with triple-negative breast cancer (TNBC) are not candidates for targeted therapy, leaving chemotherapy as the primary treatment option. Recently, immunotherapy has demonstrated promising results in TNBC, due to its immunogenicity. In addition, a novel antibody-drug conjugate, namely, trastuzumab-deruxtecan, has shown effectiveness in TNBC patients with low-HER2 expression (HER2-low). These novel treatment options raise the question about the potential association between the density of stromal tumor-infiltrating lymphocytes (sTILs) and the level of HER2 expression. We aimed to evaluate the association between the level of HER2 expression (HER2-low versus HER2-0) and density of sTILs in TNBC patients, and how they impact the response to neoadjuvant chemotherapy (NAC). This was a retrospective multicenter study including all TNBC patients diagnosed between 2018 and 2022. Central pathology review included sTILs percentages and level of HER2 expression. Tumors were reclassified as either HER2-0 (HER2 IHC 0) or HER2-low (IHC 1 + or 2 + with negative reflex test). Various clinicopathologic characteristics, including sTILs density, and response to NAC were compared between HER2-0 and HER2-low cases. In total, 753 TNBC patients were included in this study, of which 292 patients received NAC. Interobserver agreement between the original pathology report and central review was moderate (77% had the same IHC status after reclassification in either HER2-0 or HER2-low; k = 0.45). HER2-low TNBC represented about one third (36%) of the tumors. No significant difference in sTILs density or complete pathologic response rate was found between HER2-0 and HER2-low cases (p = 0.476 and p = 0.339, respectively). The density of sTILs (≥ 10% sTILs vs. < 10%) was independently associated with achieving a pCR (p = 0.011). In conclusion, no significant association was found between HER2-low status and density of sTILs nor response to NAC. Nonetheless, sTILs could be an independent biomarker for predicting NAC response in TNBC patients.

Validation and Clinical Utility of a Prediction Model for the Risk of Upstaging to Invasive Breast Cancer After a Biopsy Diagnosis Ductal Carcinoma In Situ.

BACKGROUND: This study aimed to validate the DCIS-upstage model, a previously developed model to predict the risk of upstaging to invasive breast cancer in patients with biopsy-proven ductal carcinoma in situ (DCIS) in a more recent cohort and to assess the model's clinical utility. METHODS: The model was validated in a registry cohort (n = 2269) and in an institution cohort (n = 302). A calibration plot was made, followed by a decision curve analysis (DCA). The model's area under the curve (AUC) was compared with the AUC of another published model and with the AUCs of new models using the risk factors of the DCIS-upstage model and additional risk factors. RESULTS: The DCIS-upstage model had an AUC of 0.67 at development; in the validation, the AUC was 0.65 in the registry cohort and 0.73 in the institution cohort. The DCA showed that the model has clinical utility. The other published model had an AUC of 0.66 in the institution cohort. Adding risk factors to the DCIS-upstage model slightly increased the AUC. CONCLUSIONS: The DCIS-upstage prediction model is valid in other cohorts. The model has clinical utility and may be used to select patients with biopsy-proven DCIS for sentinel lymph node biopsy.

A low risk of recurrence after breast-conserving surgery for DCIS: A single-institution experience.

BACKGROUND: Previously published studies report up to 30% recurrence rates after DCIS, so it would be desirable to identify those women at risk for recurrence and adapt adjuvant management. This study aimed to identify the locoregional recurrence rate after breast conserving surgery (BCS) for DCIS, and to evaluate the possible role of immunohistochemical (IHC) staining in predicting the risk of recurrence. PATIENTS AND METHODS: In a retrospective cohort study, patients who underwent BCS for pure DCIS were identified. Data on well-established clinical-pathological risk factors and development of locoregional recurrence was gathered from patient files. In addition, IHC stains of ER, PR, HER2, p53, and ki67 were performed on original tumor samples. Univariable Cox regression analyses were performed to identify possible risk factors for locoregional recurrence. RESULTS: 190 patients were included. At a median follow-up time of 12.8 years fifteen (8%) patients developed locoregional recurrence: 7 invasive cancer and 8 DCIS. These recurrences were diagnosed within a range of 1.7 to 19.6 years after the initial diagnosis. Univariable Cox regression analysis did only show a significant association between p53 and locoregional recurrence. Our re-excision rate to obtain free margins was 30.5%, and 90% received radiotherapy. Endocrine treatment was not used. CONCLUSIONS: At 12.8 years follow-up, patients with DCIS treated with BCS have a very low locoregional recurrence of 8%. Although we could demonstrate that increased p53 expression is a risk factor for locoregional recurrence, we think this is of little clinical value in our population with such a low recurrence rate. MICROABSTRACT: With a published recurrence rate up to 30% after DCIS, it would be desirable to identify those at risk to adapt treatment and follow-up. We aimed to evaluate the role of immunohistochemical staining to determine the risk of locoregional recurrence, in addition to established clinical and pathological risk factors. At a median follow-up of 12.8 years, we found a locoregional recurrence rate of 8%. Increased expression of p53 is associated with an increased risk of locoregional recurrence.

Interobserver Variation in the Assessment of Immunohistochemistry Expression Levels in HER2-Negative Breast Cancer: Can We Improve the Identification of Low Levels of HER2 Expression by Adjusting the Criteria? An International Interobserver Study.

The classification of human epidermal growth factor receptor 2 (HER2) expression is optimized to detect HER2-amplified breast cancer (BC). However, novel HER2-targeting agents are also effective for BCs with low levels of HER2. This raises the question whether the current guidelines for HER2 testing are sufficiently reproducible to identify HER2-low BC. The aim of this multicenter international study was to assess the interobserver agreement of specific HER2 immunohistochemistry scores in cases with negative HER2 results (0, 1+, or 2+/in situ hybridization negative) according to the current American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines. Furthermore, we evaluated whether the agreement improved by redefining immunohistochemistry (IHC) scoring criteria or by adding fluorescent in situ hybridization (FISH). We conducted a 2-round study of 105 nonamplified BCs. During the first assessment, 16 pathologists used the latest version of the ASCO/CAP guidelines. After a consensus meeting, the same pathologists scored the same digital slides using modified IHC scoring criteria based on the 2007 ASCO/CAP guidelines, and an extra "ultralow" category was added. Overall, the interobserver agreement was limited (4.7% of cases with 100% agreement) in the first round, but this was improved by clustering IHC categories. In the second round, the highest reproducibility was observed when comparing IHC 0 with the ultralow/1+/2+ grouped cluster (74.3% of cases with 100% agreement). The FISH results were not statistically different between HER2-0 and HER2-low cases, regardless of the IHC criteria used. In conclusion, our study suggests that the modified 2007 ASCO/CAP criteria were more reproducible in distinguishing HER2-0 from HER2-low cases than the 2018 ASCO/CAP criteria. However, the reproducibility was still moderate, which was not improved by adding FISH. This could lead to a suboptimal selection of patients eligible for novel HER2-targeting agents. If the threshold between HER2 IHC 0 and 1+ is to be clinically actionable, there is a need for clearer, more reproducible IHC definitions, training, and/or development of more accurate methods to detect this subtle difference in protein expression levels.

Risk of metachronous contralateral breast cancer in patients with primary invasive lobular breast cancer: Results from a nationwide cohort.

Lobular primary breast cancer (PBC) histology has been proposed as a risk factor for contralateral breast cancer (CBC), but results have been inconsistent. We investigated CBC risk and the impact of systemic therapy in lobular versus ductal PBC. Further, CBC characteristics following these histologic subtypes were explored. We selected 74,373 women diagnosed between 2003 and 2010 with stage I-III invasive PBC from the nationwide Netherlands Cancer Registry. We assessed absolute risk of CBC taking into account competing risks among those with lobular (n = 8903), lobular mixed with other types (n = 3512), versus ductal (n = 62,230) histology. Hazard ratios (HR) for CBC were estimated in a cause-specific Cox model, adjusting for age at PBC diagnosis, radiotherapy, chemotherapy and/or endocrine therapy. Multivariable HRs for CBC were 1.18 (95% CI: 1.04-1.33) for lobular and 1.37 (95% CI: 1.16-1.63) for lobular mixed versus ductal PBC. Ten-year cumulative CBC incidences in patients with lobular, lobular mixed versus ductal PBC were 3.2%, 3.6% versus 2.8% when treated with systemic therapy and 6.6%, 7.7% versus 5.6% in patients without systemic therapy, respectively. Metachronous CBCs were diagnosed in a less favourable stage in 19%, 26% and 23% and less favourable differentiation grade in 22%, 33% and 27% than the PBCs of patients with lobular, lobular mixed and ductal PBC, respectively. In conclusion, lobular and lobular mixed PBC histology are associated with modestly increased CBC risk. Personalised CBC risk assessment needs to consider PBC histology, including systemic treatment administration. The impact on prognosis of CBCs with unfavourable characteristics warrants further evaluation.

Predicting Lymph Node Metastases in Patients with Biopsy-Proven Ductal Carcinoma In Situ of the Breast: Development and Validation of the DCIS-met Model.

PURPOSE: In patients with a biopsy-proven ductal carcinoma in situ (DCIS), axillary staging is frequently performed, but in hindsight often turns out to be superfluous. The aim of this observational study was to develop a prediction model for risk of lymph node metastasis in patients with a biopsy-proven DCIS. METHODS: Data were received from the Dutch Pathology Databank and the Netherlands Cancer Registry. The population-based cohort consisted of all biopsy-proven DCIS patients diagnosed in the Netherlands in 2011 and 2012. The prediction model was evaluated with the area under the curve (AUC) of the receiver operating characteristic, and a calibration plot and a decision curve analysis and was validated in a Dutch cohort of patients diagnosed in the period 2016-2019. RESULTS: Of 2892 biopsy-proven DCIS patients, 127 had metastasis (4.4%). Risk factors were younger age (OR = 0.97, 95% CI 0.95-0.99), DCIS not detected by screening (OR = 1.55, 95% CI 1.01-2.38), suspected invasive component at biopsy (OR = 1.86, 95% CI 1.01-3.41), palpable tumour (OR = 2.06, 95% CI 1.34-3.18), BI-RADS score 5 (OR = 2.41, 95% CI 1.53-3.78), intermediate-grade DCIS (OR = 3.01, 95% CI 1.27-7.15) and high-grade DCIS (OR = 3.20, 95% CI 1.36-7.54). For 24% (n = 708) of the patients, the predicted risk of lymph node metastasis was above 5%. Based on the decision curve analysis, the model had a net benefit for a predicted risk below 25%. The AUC was 0.745. Of the 2269 patients in the validation cohort, 53 (2.2%) had metastasis and the AUC was 0.741. CONCLUSIONS: This DCIS-met model can support clinical decisions on axillary staging in patients with biopsy-proven DCIS.

Changes in breast cancer treatment during the COVID-19 pandemic: a Dutch population-based study.

PURPOSE: We aimed to compare (1) treatments and time intervals between treatments of breast cancer patients diagnosed during and before the COVID-19 pandemic, and (2) the number of treatments started during and before the pandemic. METHODS: Women were selected from the Netherlands Cancer Registry. For aim one, odds ratios (OR) and 95% confidence intervals (95%CI) were calculated to compare the treatment of women diagnosed within four periods of 2020: pre-COVID (weeks 1-8), transition (weeks 9-12), lockdown (weeks 13-17), and care restart (weeks 18-26), with data from 2018/2019 as reference. Wilcoxon rank-sums test was used to compare treatment intervals, using a two-sided p-value < 0.05. For aim two, number of treatments started per week in 2020 was compared with 2018/2019. RESULTS: We selected 34,097 women for aim one. Compared to 2018/2019, neo-adjuvant chemotherapy was less likely for stage I (OR 0.24, 95%CI 0.11-0.53), stage II (OR 0.63, 95%CI 0.47-0.86), and hormone receptor+/HER2- tumors (OR 0.55, 95%CI 0.41-0.75) diagnosed during transition. Time between diagnosis and first treatment decreased for patients diagnosed during lockdown with a stage I (p < 0.01), II (p < 0.01) or III tumor (p = 0.01). We selected 30,002 women for aim two. The number of neo-adjuvant endocrine therapies and surgeries starting in week 14, 2020, increased by 339% and 18%, respectively. The number of adjuvant chemotherapies decreased by 42% in week 15 and increased by 44% in week 22. CONCLUSION: The pandemic and subsequently altered treatment recommendations affected multiple aspects of the breast cancer treatment strategy and the number of treatments started per week.

Expression and Localization of Ferritin-Heavy Chain Predicts Recurrence for Breast Cancer Patients with a BRCA1/2 Mutation.

The ferritin-heavy chain (FTH1) is the catalytic subunit of the ferroxidase ferritin, which prevents oxidative DNA damage via intracellular iron storage. FTH1 was shown to be a prognostic marker for triple-negative breast cancer (BC) patients and associated with an enrichment of CD8+ effector T cells. However, whether the expression and localization of FTH1 are also associated with clinical outcome in other BC subtypes is unknown. Here, we investigated the association of FTH1 with time to survival in BCs from 222 BRCA1/2 mutation carriers by immunohistochemistry on tissue microarrays. In addition, for 51 of these patients, the association between FTH1 and specific subsets of T cells was evaluated on whole slides using automatic scoring algorithms. We revealed that nuclear FTH1 (nFTH1) expression, in multivariable analyses, was associated with a shorter disease-free (HR = 2.71, 95% CI = 1.49-4.92, p = 0.001) and metastasis-free survival (HR = 3.54, 95% CI = 1.45-8.66, p = 0.006) in patients carrying a BRCA1/2 mutation. However, we found no relation between cytoplasmic FTH1 expression and survival of BRCA1/2 mutation carriers. Moreover, we did not detect an association between FTH1 expression and the amount of CD45+ (p = 0.13), CD8+ (p = 0.18), CD4+ (p = 0.20) or FOXP3+ cells (p = 0.17). Consequently, the mechanism underlying the worse recurrence-free survival of nFTH1 expression in BRCA1/2 mutation carriers needs further investigation.

Gastric metastasis of breast cancer: A frequent mimicker of primary gastric cancer in breast cancer patients.

Gastric metastasis of breast cancer is a known mimicker of primary gastric cancer. This paper demonstrates that in patients with a history of breast cancer, gastric metastasis and primary gastric cancer are equally likely.

Surgeons' preferences for using sentinel lymph node biopsy in patients with ductal carcinoma in situ.

BACKGROUND: There is a large variation between Dutch hospitals in the use of Sentinel Lymph Node Biopsy (SLNB) in patients with a biopsy diagnosis of Ductal Carcinoma in Situ. The aim of our study was to investigate whether this variation might be explained by preferences of surgeons, organisational factors or the influence of patients preferences. METHODS: A cross-sectional web survey was conducted among 260 Dutch oncological/breast surgeons. Preferences of surgeons and the influence of the patients' preferences were determined by means of best-worst scaling (BWS) of profile case scenarios and by ranking risk factors. The survey also explored organisational questions, the reported use of diagnostic techniques and influences on the decision. RESULTS: The BWS scenarios were completed by 57 surgeons. The most important reasons for performing SLNB were a suspected invasive component and DCIS grade 3. In the ranking, these were also the first and second most important factor, followed by the size of the lesion and a mass on mammogram. In 58% to 70% of the scenarios, the surgeons would not change their decisions on the use of SLNB if the patient's chose differed. No organisational factor was significantly associated with the reported use of SLNB. CONCLUSION: The inter-hospital variation in the use of SLNB could not be attributed to organisational factors or surgeons' preferences for risk factors. The risk factors that most surgeons reported as reasons for performing SLNB are consistent with the factors described in the Dutch treatment guideline for the use of SLNB.

Interobserver Agreement of PD-L1/SP142 Immunohistochemistry and Tumor-Infiltrating Lymphocytes (TILs) in Distant Metastases of Triple-Negative Breast Cancer: A Proof-of-Concept Study. A Report on Behalf of the International Immuno-Oncology Biomarker Working Group.

Patients with advanced triple-negative breast cancer (TNBC) benefit from treatment with atezolizumab, provided that the tumor contains ≥1% of PD-L1/SP142-positive immune cells. Numbers of tumor-infiltrating lymphocytes (TILs) vary strongly according to the anatomic localization of TNBC metastases. We investigated inter-pathologist agreement in the assessment of PD-L1/SP142 immunohistochemistry and TILs. Ten pathologists evaluated PD-L1/SP142 expression in a proficiency test comprising 28 primary TNBCs, as well as PD-L1/SP142 expression and levels of TILs in 49 distant TNBC metastases with various localizations. Interobserver agreement for PD-L1 status (positive vs. negative) was high in the proficiency test: the corresponding scores as percentages showed good agreement with the consensus diagnosis. In TNBC metastases, there was substantial variability in PD-L1 status at the individual patient level. For one in five patients, the chance of treatment was essentially random, with half of the pathologists designating them as positive and half negative. Assessment of PD-L1/SP142 and TILs as percentages in TNBC metastases showed poor and moderate agreement, respectively. Additional training for metastatic TNBC is required to enhance interobserver agreement. Such training, focusing on metastatic specimens, seems worthwhile, since the same pathologists obtained high percentages of concordance (ranging from 93% to 100%) on the PD-L1 status of primary TNBCs.

Trends in incidence, treatment, survival and subsequent breast cancer in lobular carcinoma in situ in the Netherlands: A population-based analysis.

PURPOSE: We analysed incidence, treatment, survival, occurrence of ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC) after lobular carcinoma in situ (LCIS) in the Netherlands. METHODS: All women diagnosed with classic LCIS between 1989 and 2017 were identified from the Netherlands Cancer Registry. We calculated overall (OS), relative survival (RS) and cumulative incidence functions (CIF, accounting for competing risks) of mortality, DCIS and IBC. For IBC, standardised incidence ratios (SIR) of IBC were calculated. Analyses were stratified for surgical treatment. RESULTS: We included 1890 patients. Median age was 51 years. Median follow-up was 8.5 years. In 1989-2017, LCIS incidence increased from 41 to 124, surgical treatment decreased from 100% to 41.1 % - mostly BCS. 10-year OS and 20-year RS exceeded 90 % in all subgroups. Overall, 48 (2.5 %) and 270 (14.3 %) patients were diagnosed with DCIS and IBC. IBCs were mostly early-stage. After mastectomy, 13 of 14 IBCs presented contralaterally. In the other groups, 64.8-70.9 % of IBCs presented ipsilaterally, 34.5-53.9 % of these were lobular. The SIR of ipsilateral IBC was highest after no surgery (6.9, 95%CI:4.9-9.4), lowest after mastectomy (0.2, 95%CI:0.4-0.8). CONCLUSION: LCIS incidence increased, surgical treatment decreased. The low mortality risks support consideration of active surveillance. However, the increased IBC incidence suggests careful monitoring.

Transcriptomic Properties of HER2+ Ductal Carcinoma In Situ of the Breast Associate with Absence of Immune Cells.

The identification of transcriptomic alterations of HER2+ ductal carcinoma in situ (DCIS) that are associated with the density of tumor-infiltrating lymphocytes (TILs) could contribute to optimizing choices regarding the potential benefit of immune therapy. We compared the gene expression profile of TIL-poor HER2+ DCIS to that of TIL-rich HER2+ DCIS. Tumor cells from 11 TIL-rich and 12 TIL-poor DCIS cases were micro-dissected for RNA isolation. The Ion AmpliSeq Transcriptome Human Gene Expression Kit was used for RNA sequencing. After normalization, a Mann-Whitney rank sum test was used to analyze differentially expressed genes between TIL-poor and TIL-rich HER2+ DCIS. Whole tissue sections were immunostained for validation of protein expression. We identified a 29-gene expression profile that differentiated TIL-rich from TIL-poor HER2+ DCIS. These genes included CCND3, DUSP10 and RAP1GAP, which were previously described in breast cancer and cancer immunity and were more highly expressed in TIL-rich DCIS. Using immunohistochemistry, we found lower protein expression in TIL-rich DCIS. This suggests regulation of protein expression at the posttranslational level. We identified a gene expression profile of HER2+ DCIS cells that was associated with the density of TILs. This classifier may guide towards more rationalized choices regarding immune-mediated therapy in HER2+ DCIS, such as targeted vaccine therapy.

Impact of the suspension and restart of the Dutch breast cancer screening program on breast cancer incidence and stage during the COVID-19 pandemic.

The COVID-19 pandemic forced the Dutch national breast screening program to a halt in week 12, 2020. In week 26, the breast program was resumed at 40% capacity, which increased to 60% in week 34. We examined the impact of the suspension and restart of the screening program on the incidence of screen-detected and non-screen-detected breast cancer. We selected women aged 50-74, diagnosed during weeks 2-35 of 2018 (n = 7250), 2019 (n = 7302), or 2020 (n = 5306), from the Netherlands Cancer Registry. Weeks 2-35 were divided in seven periods, based on events occurring at the start of the COVID-19 pandemic. Incidence of screen-detected and non-screen-detected tumors was calculated overall and by age group, cT-stage, and cTNM-stage for each period in 2020, and compared to the incidence in the same period of 2018/2019 (averaged). The incidence of screen-detected tumors decreased during weeks 12-13, reached almost zero during weeks 14-25, and increased during weeks 26-35. Incidence of non-screen-detected tumors decreased to a lesser extent during weeks 12-16. The decrease in incidence was seen in all age groups and mainly occurred for cTis, cT1, DCIS, and stage I tumors. Due to the suspension of the breast cancer screening program, and the restart at reduced capacity, the incidence of screen-detected breast tumors decreased by 67% during weeks 9-35 2020, which equates to about 2000 potentially delayed breast cancer diagnoses. Up to August 2020 there was no indication of a shift towards higher stage breast cancers after restart of the screening.

Ten years follow-up of histologically benign calcifications in the breast after vacuum-assisted stereotactic biopsy (VASB): Is additional mammographic follow-up warranted?

OBJECTIVE: This study assessed the short-term and the long-term breast cancer rate in patients with benign histopathologic results after a vacuum-assisted stereotactic biopsy (VASB) for calcifications. METHODS: In a retrospective cohort study, all consecutive patients who had a benign diagnosis after VASB to analyze breast calcifications. Data of breast cancer development at short-term (four years) and long-term follow-up was gathered. Breast cancer rates in our cohort were compared to the breast cancer incidence in the general population. RESULTS: Of 1376 patients who underwent VASB to analyze breast calcifications, 823 had a benign histopathologic diagnosis. During short-term follow-up, eight patients developed breast cancer. During the mean long-term follow-up period of 9.3 ± 3.1 years, 22 patients were diagnosed with ipsilateral breast cancer. The incidence rate of breast cancer after benign biopsy was comparable to the rate in the general population. CONCLUSION: In patients with VASB-confirmed benign calcifications of the breast, we found no excess incidence of ipsilateral breast cancer during ten years follow-up. Therefore, in patients with an increased risk of breast cancer (due to a history of breast cancer or familial risk) annual mammography should be sufficient. Patients with a population-based risk may be monitored via biennial mammography by the national screening program. More frequent screening would provide no benefit.

Impact of the COVID-19 pandemic on diagnosis, stage, and initial treatment of breast cancer in the Netherlands: a population-based study.

BACKGROUND: The onset of the COVID-19 pandemic forced the Dutch national screening program to a halt and increased the burden on health care services, necessitating the introduction of specific breast cancer treatment recommendations from week 12 of 2020. We aimed to investigate the impact of COVID-19 on the diagnosis, stage and initial treatment of breast cancer. METHODS: Women included in the Netherlands Cancer Registry and diagnosed during four periods in weeks 2-17 of 2020 were compared with reference data from 2018/2019 (averaged). Weekly incidence was calculated by age group and tumor stage. The number of women receiving initial treatment within 3 months of diagnosis was calculated by period, initial treatment, age, and stage. Initial treatment, stratified by tumor behavior (ductal carcinoma in situ [DCIS] or invasive), was analyzed by logistic regression and adjusted for age, socioeconomic status, stage, subtype, and region. Factors influencing time to treatment were analyzed by Cox regression. RESULTS: Incidence declined across all age groups and tumor stages (except stage IV) from 2018/2019 to 2020, particularly for DCIS and stage I disease (p < 0.05). DCIS was less likely to be treated within 3 months (odds ratio [OR]wks2-8: 2.04, ORwks9-11: 2.18). Invasive tumors were less likely to be treated initially by mastectomy with immediate reconstruction (ORwks12-13: 0.52) or by breast conserving surgery (ORwks14-17: 0.75). Chemotherapy was less likely for tumors diagnosed in the beginning of the study period (ORwks9-11: 0.59, ORwks12-13: 0.66), but more likely for those diagnosed at the end (ORwks14-17: 1.31). Primary hormonal treatment was more common (ORwks2-8: 1.23, ORwks9-11: 1.92, ORwks12-13: 3.01). Only women diagnosed in weeks 2-8 of 2020 experienced treatment delays. CONCLUSION: The incidence of breast cancer fell in early 2020, and treatment approaches adapted rapidly. Clarification is needed on how this has affected stage migration and outcomes.