Nasopharyngeal carcinoma: nationwide trends in subtype-specific incidence and survival over 3 decades in a non-endemic area.

PURPOSE: To identify trends in incidence and survival of NPC, subdivided by EBV status and histopathological subtype, over a 30-year period in the Netherlands. METHODS: Anonymized data from the Netherlands Cancer Registry and the Dutch Nationwide Pathology Databank (PALGA) for the period 1989-2018 were linked to identify and classify NPC cases. RESULTS: Incidence of NPC remained stable, with an annual percentage change (APC) of - 0.2. (95% CI - 0.9; 0.5). EBV testing became routine only in the last decade, the incidence of EBV-positive tumors remained stable over this period (APC 1.2, 95% CI - 1.3; 3.8). An increase in EBV-negative tumors (APC: 7.1, 95% CI 2.5; 11.9) and a decrease in untested tumors were found (APC: - 10.7, 95% CI - 15.7; - 5.7). The incidence of non-keratinizing, differentiated tumors increased (APC: 3.8, (95% CI 2.2; 5.5) while the incidence of other histological subtypes remained stable. Overall survival was better in patients diagnosed after 1998 (hazard ratio 0.8, 95% CI 0.6; 0.9). EBV status, histology, stage, and age were independently associated with relative excess risk of dying, but period of diagnosis was not. CONCLUSION: Testing for EBV increased over time, and a stable incidence of EBV-positive NPC over the last 10 years. The rising incidence of non-keratinizing, differentiated NPC mirrors data from the US and suggests a shift in non-endemic regions.

Incidental findings in the bowel cancer population screening program: other polyps and malignancies - A nationwide study.

The introduction of bowel cancer population screening programs has had a profound impact on gastrointestinal pathology. While the focus is mainly on quality assurance of diagnoses relevant for the outcome of these programs (colorectal cancer and its precursors), incidental findings are increasingly diagnosed. The incidence of such findings is largely unknown. Therefore, we investigated the incidence of incidental findings within the national screening program of the Netherlands. From the Dutch nationwide pathology databank (PALGA), we retrieved all histological diagnoses of patients participating in the national bowel cancer screening program from the start in 2014 until 1/1/2021. Descriptive statistics were used. During these 7 years, in total 9407 other polyps and malignancies (262 per 10,000 colonoscopies) were diagnosed. The majority (65%) were classified as inflammatory polyps. The most common malignancies were neuroendocrine tumours (n = 198, 6 per 10,000 colonoscopies); less common were lymphomas (n = 64) and metastases (n = 33). Mesenchymal polyps, such as leiomyomas and lipomas, were relatively common (27 and 16 per 10,000 colonoscopies, respectively), in comparison with neural polyps such as perineuriomas, ganglioneuromas, and neurofibromas (respectively 3, 2, and 1 per 10,000 colonoscopies). This is the largest study into the incidence of nonconventional colorectal polyps and malignancies in a homogeneous cohort of asymptomatic patients. Several of these diagnoses may have consequences for treatment and follow-up, in particular the malignancies and detection of patients with hereditary cancer syndromes.

Detection of NTRK Fusions and TRK Expression and Performance of pan-TRK Immunohistochemistry in Routine Diagnostics: Results from a Nationwide Community-Based Cohort.

Gene fusions involving NTRK1, NTRK2, and NTRK3 are rare drivers of cancer that can be targeted with histology-agnostic inhibitors. This study aimed to determine the nationwide landscape of NTRK/TRK testing in the Netherlands and the usage of pan-TRK immunohistochemistry (IHC) as a preselection tool to detect NTRK fusions. All pathology reports in 2017-2020 containing the search term 'TRK' were retrieved from the Dutch Pathology Registry (PALGA). Patient characteristics, tumor histology, NTRK/TRK testing methods, and reported results were extracted. NTRK/TRK testing was reported for 7457 tumors. Absolute testing rates increased from 815 (2017) to 3380 (2020). Tumors were tested with DNA/RNA-based molecular assay(s) (48%), IHC (47%), or in combination (5%). A total of 69 fusions involving NTRK1 (n = 22), NTRK2 (n = 6) and NTRK3 (n = 41) were identified in tumors from adult (n = 51) and pediatric (n = 18) patients. In patients tested with both IHC and a molecular assay (n = 327, of which 29 NTRK fusion-positive), pan-TRK IHC had a sensitivity of 77% (95% confidence interval (CI), 56-91) and a specificity of 84% (95% CI, 78-88%). These results showed that pan-TRK IHC has a low sensitivity in current routine practice and warrants the introduction of quality guidelines regarding the implementation and interpretation of pan-TRK IHC.

Prevalence of KRAS p.(G12C) in stage IV NSCLC patients in the Netherlands; a nation-wide retrospective cohort study.

OBJECTIVES: The recent accelerated FDA approval of sotorasib, a highly selective KRAS G12C inhibitor, offers new opportunities for the treatment of KRAS p.(G12C)-mutated non-squamous non-small cell lung cancer (NSCLC). The objective of the current study was to the determine the prevalence of KRAS mutations in stage IV non-squamous NSCLC in The Netherlands to reveal the potential impact of upcoming KRAS targeted therapy. MATERIALS AND METHODS: All patients diagnosed with stage IV non-squamous NSCLC in 2013, 2015 and 2017 in the Netherlands were selected by linking the nation-wide Netherlands Cancer Registry (NCR) and the Dutch Pathology Registry (PALGA). Demographic and pathological variables were retrieved from the pathology reports including sex, age, KRAS mutation status, molecular test method used, and the mutation status of other genes. RESULTS: Prevalence for any KRAS mutations in codon 12/13/61/146 was 39.1%. KRAS p.(G12C) was detected in 15.5% of all non-squamous NSCLC cases representing 39.6% of all KRAS-mutant cases. National testing rate for KRAS mutations increased from 70% in 2013 to 82% in 2017. Testing techniques changed significantly over time with next generation sequencing as the main used method in 2017 (71.6%) but did not affect prevalence of KRAS mutations over time. When KRAS was tested as part of a larger panel, the KRAS p.(G12C) mutation was frequently reported with a concurrent mutation in TP53 (47.7%) or STK11 (10.3%). CONCLUSION: The high prevalence for KRAS p.(G12C) offers a promising new specific treatment option for 15% of all stage IV non-squamous NSCLC patients.

Considerable interlaboratory variation in PD-L1 positivity in a nationwide cohort of non-small cell lung cancer patients.

OBJECTIVES: Immunohistochemical expression of programmed death-ligand 1 (PD-L1) is used as a predictive biomarker for prescription of immunotherapy to non-small cell lung cancer (NSCLC) patients. Accurate assessment of PD-L1 expression is therefore crucial. In this study, the extent of interlaboratory variation in PD-L1 positivity in the Netherlands was assessed, using real-world clinical pathology data. MATERIALS AND METHODS: Data on all NSCLC patients in the Netherlands with a mention of PD-L1 testing in their pathology report from July 2017 to December 2018 were extracted from PALGA, the nationwide network and registry of histo- and cytopathology in the Netherlands. PD-L1 positivity rates were determined for each laboratory that performed PD-L1 testing, with separate analyses for histological and cytological material. Two cutoffs (1% and 50%) were used to determine PD-L1 positivity. Differences between laboratories were assessed using funnel plots with 95% confidence limits around the overall mean. RESULTS: 6,354 patients from 30 laboratories were included in the analysis of histology data. At the 1% cutoff, maximum interlaboratory variation was 39.1% (32.7%-71.8%) and ten laboratories (33.3%) differed significantly from the mean. Using the 50% cutoff, four laboratories (13.3%) differed significantly from the mean and maximum variation was 23.1% (17.2%-40.3%). In the analysis of cytology data, 1,868 patients from 23 laboratories were included. Eight laboratories (34.8%) differed significantly from the mean in the analyses of both cutoffs. Maximum variation was 41.2% (32.2%-73.4%) and 29.2% (14.7%-43.9%) using the 1% and 50% cutoffs, respectively. CONCLUSION: Considerable interlaboratory variation in PD-L1 positivity was observed. Variation was largest using the 1% cutoff. At the 50% cutoff, analysis of cytology data demonstrated a higher degree of variation than the analysis of histology data.

A Nationwide Study on the Impact of Routine Testing for EGFR Mutations in Advanced NSCLC Reveals Distinct Survival Patterns Based on EGFR Mutation Subclasses.

EGFR mutation analysis in non-small-cell lung cancer (NSCLC) patients is currently standard-of-care. We determined the uptake of EGFR testing, test results and survival of EGFR-mutant NSCLC patients in the Netherlands, with the overall objective to characterize the landscape of clinically actionable EGFR mutations and determine the role and clinical relevance of uncommon and composite EGFR mutations. Non-squamous NSCLC patients diagnosed in 2013, 2015 and 2017 were identified in the Netherlands Cancer Registry (NCR) and matched to the Dutch Pathology Registry (PALGA). Overall, 10,254 patients were included. Between 2013-2017, the uptake of EGFR testing gradually increased from 72.7% to 80.9% (p < 0.001). Multi-gene testing via next-generation sequencing (increased from 7.8% to 78.7% (p < 0.001), but did not affect the number of detected EGFR mutations (n = 925; 11.7%; 95% confidence interval (CI), 11.0-12.4) nor the distribution of variants. For patients treated with first-line EGFR inhibitors (n = 651), exon 19 deletions were associated with longer OS than L858R (HR 1.58; 95% CI, 1.30-1.92; p < 0.001) or uncommon, actionable variants (HR 2.13; 95% CI, 1.60-2.84; p < 0.001). Interestingly, OS for patients with L858R was similar to those with uncommon, actionable variants (HR 1.31; 95% CI, 0.98-1.75; p = 0.069). Our analysis indicates that grouping exon 19 deletions and L858R into one class of 'common' EGFR mutations in a clinical trial may mask the true activity of an EGFR inhibitor towards specific mutations.

Significant inter- and intra-laboratory variation in grading of invasive breast cancer: A nationwide study of 33,043 patients in the Netherlands.

Accurate, consistent and reproducible grading by pathologists is of key-importance for identification of individual patients with invasive breast cancer (IBC) that will or will not benefit from adjuvant systemic treatment. We studied the laboratory-specific grading variation using nationwide real-life data to create insight and awareness in grading variation. Synoptic pathology reports of all IBC resection-specimens, obtained between 2013 and 2016, were retrieved from the nationwide Dutch Pathology Registry (PALGA). Absolute differences in laboratory-proportions of Grades I-III were compared to the national reference. Multivariable logistic regression provided laboratory-specific odds ratios (ORs) for high- vs. low-grade IBC. 33,792 IBC pathology reports of 33,043 patients from 39 laboratories were included, of which 28.1% were reported as Grade I (range between laboratories 16.3-43.3%), 47.6% as Grade II (38.4-57.8%), and 24.3% as Grade III (15.5-34.3%). Based on national guidelines, the indication for adjuvant chemotherapy was dependent on histologic grade in 29.9% of patients. After case-mix correction, 20 laboratories (51.3%) showed a significantly deviant OR. Significant grading differences were also observed among pathologists within laboratories. In this cohort of 33,043 breast cancer patients, we observed substantial inter- and intra-laboratory variation in histologic grading. It can be anticipated that this has influenced outcome including exposure to unnecessary toxicity, since choice of adjuvant chemotherapy was dependent on grade in nearly a third of patients. Better standardization and training seems warranted.

Decrease of variation in the grading of dysplasia in colorectal adenomas with a national e-learning module.

AIMS: Variation in health-care is undesirable, as this is potentially harmful for patients. In the Netherlands, an e-learning module was developed to standardise pathological evaluation of colorectal adenomas. We studied the effect of e-learning on interlaboratory variability in grading of dysplasia in screened conventional colorectal adenomas. METHODS AND RESULTS: A cross-sectional retrospective study was performed, including all colorectal adenomas from the Dutch population-based colorectal cancer screening programme, retrieved from the Dutch Pathology Registry (PALGA) from January 2014 to July 2015. The e-learning tool, commissioned by the National Institute for Public Health, was implemented among screening pathologists from October 2014. Proportions of high-grade dysplasia (HGD) were compared before (January-July 2014) and after implementation (October 2014-July 2015) of the e-learning module. Interlaboratory variation was assessed by multilevel mixed-effects analysis. In total, 20 713 colonoscopies (20 546 patients) were performed after a positive faecal immunochemical screening test, resulting in the inclusion of 56 355 conventional adenomas from 37 pathology laboratories. Before implementation, 12 614 adenomas were diagnosed, including 4.3% with HGD. After implementation, 43 741 adenomas were diagnosed, and the HGD proportion decreased to 3.9%. Univariable analysis showed less deviant proportions of HGD after implementation in 62% of the laboratories (P = 0.019). Multilevel analysis confirmed decreased variation in the risk of diagnosing HGD (P = 0.021). CONCLUSIONS: Interlaboratory variability in grading HGD in colorectal adenomas after a positive screening test decreased after implementation of an e-learning module for pathologists. We therefore conclude that e-learning has a favourable influence on decreasing diagnostic variability, making this a relevant strategy for health-care standardisation.

Significant inter- and intra-laboratory variation in grading of ductal carcinoma in situ of the breast: a nationwide study of 4901 patients in the Netherlands.

PURPOSE: A considerable part of ductal carcinoma in situ (DCIS) lesions may never progress into invasive breast cancer. However, standard treatment consists of surgical excision. Trials aim to identify a subgroup of low-risk DCIS patients that can safely forgo surgical treatment based on histologic grade, which highlights the importance of accurate grading. Using real-life nationwide data, we aimed to create insight and awareness in grading variation of DCIS in daily clinical practice. METHODS: All synoptic pathology reports of pure DCIS resection specimens between 2013 and 2016 were retrieved from PALGA, the nationwide Dutch Pathology Registry. Absolute differences in proportions of grade I-III were visualized using funnel plots. Multivariable analysis was performed by logistic regression to correct for case-mix, providing odds ratios and 95% confidence intervals for high-grade (III) versus low-grade (I-II) DCIS. RESULTS: 4952 DCIS reports from 36 laboratories were included, of which 12.5% were reported as grade I (range 6.1-24.4%), 39.5% as grade II (18.2-57.6%), and 48.0% as grade III (30.2-72.7%). After correction for case-mix, 14 laboratories (38.9%) reported a significantly lower (n = 4) or higher (n = 10) proportion of high-grade DCIS than the reference laboratory. Adjusted ORs (95%CI) ranged from 0.52 (0.31-0.87) to 3.83 (1.42-10.39). Significant grading differences were also observed among pathologists within laboratories. CONCLUSION: In this cohort of 4901 patients, we observed substantial inter- and intra-laboratory variation in DCIS grading, not explained by differences in case-mix. Therefore, there is an urgent need for nationwide standardization of grading practices, especially since the future management of DCIS may alter significantly depending on histologic grade.

[National variation in molecular diagnostics in metastatic lung cancer]. / Landelijke variatie in moleculaire diagnostiek bij gemetastaseerde longkanker.

OBJECTIVE: The objective of this study is to determine at a national level whether patients with metastatic non-small cell lung cancer (NSCLC) are adequately tested for EGFR mutations and ALK rearrangement, because targeted therapy is tailored to the results of molecular diagnostics. DESIGN: Retrospective cohort study. METHOD: Data from all patients with metastatic non-squamous NSCLC diagnosed in 2013 or 2015 were identified from the Netherlands Cancer Registry, and coupled with data from the Netherlands national pathology registry (PALGA). Using information extracted from PALGA we determined what percentage of the tumours were tested for EGFR or KRAS mutations and ALK rearrangement, identified the variables that were associated with the performance of molecular diagnostics and investigated the differences between 48 laboratories. RESULTS: A total of 6,619 patients were included (2013: n = 3,195; 2015: n = 3,424). In 2013, EGFR or KRAS testing was performed on 73.1% of the tumours (variation between laboratories 30.6-91.7%); in 2015 this was 78.9% (variation 40.0-91.0%). In 2013 49.5% of the tumours without EGFR or KRAS mutations underwent ALK testing (variation between laboratories 6.3-100%) and in 2015 ALK testing was performed on 77.4% (32.5-100%). In 2015, 6 and 7 laboratories tested significantly fewer EGFR and ALK tests, respectively, than the national average. CONCLUSION: In 2013, molecular testing for EGFR and KRAS mutations and, in particular, for ALK rearrangement was suboptimal. EGFR and ALK testing was performed significantly more often in 2015. Despite this increase, there is room for improvement in a number of laboratories and hospitals, considering that some patients were possibly wrongly not eligible for targeted therapy.

Improved quality of patient care through routine second review of histopathology specimens prior to multidisciplinary meetings.

AIM: Double reading may be a valuable tool for improving quality of patient care by identifying diagnostic errors before final sign-out, but standard double reading would significantly increase costs of pathology. We assessed the added value of intradepartmental routine double reading of histopathology specimens prior to multidisciplinary meetings. METHODS: Diagnoses, treatment plans and prognoses of patients are often discussed at multidisciplinary meetings. As part of the daily routine, all pathology specimens to be discussed at upcoming multidisciplinary meetings undergo prior intradepartmental double reading. We identified all histopathology specimens from 2013 that underwent such double reading and determined major and minor discordance rates based on clinical relevance between the initial and consensus sign-out diagnoses. RESULTS: We included 6796 histopathology specimens that underwent double reading, representing approximately 8% of all histopathology cases at our institution in 2013. Double reading diagnoses were concordant in 6566 specimens (96.6%). Major and minor discordances were observed in 60 (0.9%) and 170 (2.5%) specimens, respectively. Urology specimens had significantly more discordances than other tissues of origin, Gleason grading of prostate cancer biopsies being the most frequent diagnostic problem. Furthermore, premalignant and malignant cases showed significantly higher discordance rates than the rest. The vast majority (90%) of discordances represented changes within the same diagnostic category (eg, malignant to malignant). CONCLUSIONS: Routine double reading of histopathology specimens prior to multidisciplinary meetings prevents diagnostic errors. It resulted in about 1% discordant diagnoses of potential clinical significance, indicating that second review is worthwhile in terms of patient safety and quality of patient care.

Interlaboratory Variability in the Histologic Grading of Colorectal Adenocarcinomas in a Nationwide Cohort.

Differentiation grade of colorectal adenocarcinoma (CRC) is a prognostic factor and important for therapy selection. In patients with stage II colon cancer, poor differentiation is an indication for adjuvant chemotherapy. The variability in daily practice in the grading of CRC was assessed in a nationwide cohort. Using the Dutch Pathology Registry (PALGA), all synoptically reported CRC resections from 2010 to 2013 were identified. Proportions of poorly differentiated (PD) adenocarcinomas were determined and compared between 35 laboratories by univariable and multivariable logistic regression analyses. In total, 11,719 resections of 11,681 patients were included, of which 1427 (12.2%) were PD (range between 35 laboratories: 5.0% to 33.2%). After adjustment for case mix, 4 (11%) laboratories still reported a significantly lower (n=2) or higher (n=2) proportion of PD adenocarcinoma compared with the reference laboratory. Seven of 8 investigated laboratories showed considerable intralaboratory variation between pathologists as well. In a subgroup of 2812 patients (2813 tumors) who could have been eligible for adjuvant chemotherapy solely on the basis of the differentiation grade (stage II colon cancer patients without other high-risk factors [ie, T4, <10 lymph nodes evaluated, perforation, ileus, or angioinvasion]), 258 (9.2%) were PD (range between laboratories: 0% to 22.7%). In this subgroup, 4 laboratories still diagnosed significantly more PD adenocarcinomas after multivariable logistic regression analysis, increasing the number of colon cancer patients eligible for adjuvant therapy. In conclusion, this large nationwide cohort demonstrates considerable interlaboratory and intralaboratory variation in differentiation grading of CRC. Better standardization of grading criteria is needed for optimal determination of prognosis and treatment selection.

Interlaboratory variability in the grading of dysplasia in a nationwide cohort of colorectal adenomas.

AIMS: Although high-grade dysplasia (HGD) is a risk factor for malignant transformation and the future development of adenomas/carcinomas, grade is not incorporated in the Dutch guidelines for colonoscopy surveillance, partly because of presumed interobserver variability. The aim of this study was to analyse, in a nationwide cohort of colorectal adenomas, the interlaboratory variability in the grading of dysplasia in daily practice. METHODS AND RESULTS: From the Dutch Pathology Registry, all synoptically reported classic adenomas in The Netherlands in 2013 were identified. The proportion of adenomas with HGD was determined for biopsies and polypectomies, and compared between 37 laboratories by the use of multivariable logistic regression analyses. In total, 21 030 colonoscopies of 20 270 patients were included. HGD was reported in 530 (3.6%) of 14 866 adenomas diagnosed on biopsies (range between laboratories: 0-13.6%) and in 983 (11.8%) of 8346 adenomas diagnosed on polypectomies (range: 3.1-42.9%). After adjustment for case mix, 13 (35%) laboratories reported a significantly lower or higher frequency of HGD than average. CONCLUSIONS: We observed considerable interlaboratory variation in the grading of dysplasia in colorectal adenomas, which could be only partly explained by differences in case mix. Therefore, better standardization of grading criteria is needed before grade of dysplasia can usefully be incorporated in colonoscopy surveillance guidelines.

Improved cytodiagnostics and quality of patient care through double reading of selected cases by an expert cytopathologist.

Double reading may be a valuable tool for improving the quality of patient care by restoring diagnostic errors before final sign-out, but standard double reading would significantly increase costs of pathology. The aim of this study was to assess the added value of routine double reading of defined categories of clinical cytology specimens by specialized cytopathologists. Specialized cytopathologists routinely re-diagnosed blinded defined categories of clinical cytology specimens that had been signed out by routine pathologists from January 2012 up to December 2013. Major and minor discordance rates between initial and expert diagnoses were determined, and both diagnoses were validated by comparison with same-site histological follow-up. Initial and expert diagnoses were concordant in 131/218 specimens (60.1 %). Major and minor discordances were present in 28 (12.8 %) and 59 (27.1 %) specimens, respectively. Pleural fluid, thyroid and urine specimens showed the highest major discordance rates (19.4, 19.2 and 16.7 %, respectively). Histological follow-up (where possible) supported the expert diagnosis in 95.5 % of specimens. Our implemented double reading strategy of defined categories of cytology specimens showed major discordance in 12.8 % of specimens. The expert diagnosis was supported in 95.5 % of discordant cases where histological follow-up was available. This indicates that this double reading strategy is worthwhile and contributes to better cytodiagnostics and quality of patient care, especially for suspicious pleural fluid, thyroid and urine specimens. Our results emphasize that cytopathology is a subspecialization of pathology and requires specialized cytopathologists.

The value of autopsies in the era of high-tech medicine: discrepant findings persist.

AIMS: Although the autopsy is still the gold standard for quality assessment of clinical diagnoses, autopsy rates have been declining over the last decades to <10%. The aim of this study was to investigate the value of autopsies in the high-tech medicine era by determining the frequency of discrepancies between clinical and autopsy diagnoses. METHODS: We classified all adult autopsy cases (n=460), performed at Symbiant, Pathology Expert Centre, in 2007 and 2012/2013, as having major, or minor discrepancy or total concordance. The roles of possible contributory factors were analysed. Finally, we assessed the role of microscopic examination in identifying cause of death. RESULTS: Major and minor discrepancies were found in 23.5% and 32.6% of the classifiable autopsies, respectively. Most commonly observed major discrepancies were myocardial infarction, pulmonary embolism and pneumonia. Improper imaging and discontinuation of active treatment were significantly associated with a higher and a lower frequency of major discrepancies, respectively. Comparing 2007 and 2012/2013, the frequency of minor discrepancies significantly increased from 26.8% to 39.3%. Final admission length of >2 days was significantly associated with a lower frequency of class III minor discrepancies. Microscopic examination contributed to establishing cause of death in 19.6% of the cases. CONCLUSIONS: Discrepant findings persist at autopsy, even in the era of high-tech medicine. Therefore, autopsies still should serve as a very important part of quality control in clinical diagnosis and treatment. Learning from individual and system-related diagnostic errors can aid in improving patient safety.

Added value of HER-2 amplification testing by multiplex ligation-dependent probe amplification in invasive breast cancer.

BACKGROUND: HER-2 is a prognostic and predictive marker, but as yet no technique is perfectly able to identify patients likely to benefit from HER-2 targeted therapies. We aimed to prospectively assess the added value of first-line co-testing by IHC, and multiplex ligation-dependent probe amplification (MLPA) and chromogenic in situ hybridization (CISH). METHODS: As local validation, HER-2 MLPA and CISH were compared in 99 breast cancers. Next, we reviewed 937 invasive breast cancers, from 4 Dutch pathology laboratories, that were prospectively assessed for HER-2 by IHC and MLPA (and CISH in selected cases). RESULTS: The validation study demonstrated 100% concordance between CISH and MLPA, if both methods were assessable and conclusive (81.8% of cases). Significant variation regarding percentages IHC 0/1+ and 2+ cases was observed between the laboratories (p<0.0001). Overall concordance between IHC and MLPA/CISH was 98.1% (575/586) (Kappa = 0.94). Of the IHC 3+ cases, 6.7% failed to reveal gene amplification, whereas 0.8% of the IHC 0/1+ cases demonstrated gene amplification. Results remained discordant after retrospective review in 3/11 discordant cases. In the remaining 8 cases the original IHC score was incorrect or adapted after repeated IHC staining. CONCLUSIONS: MLPA is a low-cost and quantitative high-throughput technique with near perfect concordance with CISH. The use of MLPA in routinely co-testing all breast cancers may reduce HER-2 testing variation between laboratories, may serve as quality control for IHC, will reveal IHC 0/1+ patients with gene amplification, likely responsive to trastuzumab, and identify IHC 3+ cases without gene amplification that may respond less well.