The admixed brushtail possum genome reveals invasion history in New Zealand and novel imprinted genes.

Combining genome assembly with population and functional genomics can provide valuable insights to development and evolution, as well as tools for species management. Here, we present a chromosome-level genome assembly of the common brushtail possum (Trichosurus vulpecula), a model marsupial threatened in parts of their native range in Australia, but also a major introduced pest in New Zealand. Functional genomics reveals post-natal activation of chemosensory and metabolic genes, reflecting unique adaptations to altricial birth and delayed weaning, a hallmark of marsupial development. Nuclear and mitochondrial analyses trace New Zealand possums to distinct Australian subspecies, which have subsequently hybridised. This admixture allowed phasing of parental alleles genome-wide, ultimately revealing at least four genes with imprinted, parent-specific expression not yet detected in other species (MLH1, EPM2AIP1, UBP1 and GPX7). We find that reprogramming of possum germline imprints, and the wider epigenome, is similar to eutherian mammals except onset occurs after birth. Together, this work is useful for genetic-based control and conservation of possums, and contributes to understanding of the evolution of novel mammalian epigenetic traits.

Enhanced down-regulation of ALCAM/CD166 in African-American Breast Cancer.

BACKGROUND: Variation in tumor biology in African-American (AA) and Caucasian (CAU) women with breast cancer is poorly defined. Activated leukocyte cell adhesion molecule (ALCAM) is a bad prognostic factor of breast cancer yet it has never being studied in the AA population. We tested the hypothesis that ALCAM expression would be markedly lower in cases of AA breast cancer when compared to CAU. METHODS: Cases of breast cancer among AA (n = 78) and CAU (n = 95) women were studied. Immunohistochemical staining was used to semi-quantitatively score ALCAM expression in tumor and adjacent non-tumor breast tissues. Clinico-pathological characteristics including histological type, histological grade, tumor size, lymph node metastasis, estrogen receptor (ER), progesterone receptor (PR), and HER2-neu status were abstracted, and their association with ALCAM expression tested. RESULTS: Univariate analysis revealed that the level of ALCAM expression at intercellular junctions of primary tumors correlates with histological grade (AA; p = 0.04, CUA; p = 0.02), ER status (AA; p = 0.0004, CAU; p = 0.0015), PR status (AA; p = 0.002, CUA p = 0.034) and triple-negative tumor status (AA; p = 0.0002, CAU; p = 0.0006,) in both ethnic groups. Multivariate analysis demonstrated that ethnicity contribute significantly to ALCAM expression after accounting for basal-like subtype, age, histological grade, tumor size, and lymph node status. Compared to CAU tumors, the AA are 4 times more likely to have low ALCAM expression (p = 0.003). CONCLUSIONS: Markedly low expression of ALCAM at sites of cell-cell contact in primary breast cancer tumors regardless of differentiation, size and lymph node involvement may contribute to the more aggressive phenotype of breast cancer among AA women.

Breast arterial calcification in chronic kidney disease: absence of smooth muscle apoptosis and osteogenic transdifferentiation.

The pathophysiology of medial arterial calcification in chronic kidney disease (CKD) is unclear but has been ascribed to phenotypic changes in vascular smooth muscle, possibly in conjunction with intimal proliferation and atherosclerosis. As the prevalence of calcification in breast arteries is increased in women with CKD and end-stage renal disease (ESRD), this was examined histologically in mastectomy specimens from 19 women with CKD or ESRD. Arterial calcification was present in 18, was exclusively medial, and occurred in vessels as small as arterioles. Intimal thickening was common but unrelated to calcification. There was no evidence of atherosclerosis. The earliest calcification presented as small punctate lesions scattered throughout the media, often with calcification of the internal elastic lamina. Arterial calcification was present in all samples from an age- and diabetes-matched cohort without CKD but was much milder. While smooth muscle cell density was reduced one-third in arteries from patients with ESRD, the cells appeared normal, expressed SM22α, and exhibited no apoptosis. Staining for the bone-specific protein osteocalcin, the osteoblastic transcription factors Runx2 or osterix, or the chondrocytic transcription factor SOX9 was absent in regions of early calcification. Thus, medial calcification in breast arteries of patients with CKD can occur in the absence of smooth muscle cell apoptosis and/or osteogenic transdifferentiation. This suggests that the pathologic mineralization process may differ from one arterial type to the other.

Triple-negative breast carcinoma in African American and Caucasian women: clinicopathology, immunomarkers, and outcome.

PURPOSE: Breast cancers are often classified on the presence/absence of hormone receptors, and growth factor oncogenes (estrogen receptor, progesterone receptor, HER2). Triple-negative breast cancers, negative for these markers, do not benefit from targeted therapy. We compared clinicopathologic parameters and immunohistochemical markers of prognostic and/or predictive significance, and outcome between African American and Caucasian triple-negative breast cancer patients. METHODS: Invasive triple-negative breast cancers from African American (n=94) and Caucasian (n=68) patients were studied. Clinicopathologic features (age, tumor size, grade, lymph node status, angiolymphatic invasion, visceral metastases) and survival (overall and progression free) were compared. Marker expression (CK5, CK7, CK8, CK14, CK18, CK19, vimentin, CD44, c-Kit, epidermal growth factor receptor, p-cadherin, p53, p63, topoisomerase II, androgen receptor, Ki-67) was assessed in tissue microarrays. RESULTS: Significant differences between African American and Caucasian women were observed for mean age and tumor size. African Americans had a trend toward greater lymph node involvement than Caucasians. The following markers were found in significantly different frequencies between the 2 groups: CK5, CK8, CK19, c-Kit, androgen receptor, and high Ki-67. African Americans show shorter overall and progression-free survival. Other clinicopathologic parameters, markers, and outcome were present at similar frequencies. DISCUSSION: African American triple-negative breast cancers were more aggressive, occurring at a younger age, being larger, with higher proliferation, patients more frequently dying of disease, and with a trend toward positive lymph node status. Heterogeneity of marker expression suggests variation in the genetics of breast carcinomas in different races.

The predictive ability of a CK5/p63/CK8/18 antibody cocktail in stratifying breast papillary lesions on needle biopsy: an algorithmic approach works best.

OBJECTIVES: Immunohistochemical markers have been shown to assist in the stratification of breast papillary lesions. We evaluated the ability of different cytokeratin (CK) and p63 expression profiles on needle biopsy specimens to predict excision diagnoses. METHODS: A CK5/p63/CK8/18 antibody cocktail was applied to 58 needle biopsy specimens (32 papillomas, 7 atypical papillomas, 19 papillary carcinomas on excision). RESULTS: p63 expression was greater in papillomas than in atypical papillomas (P = .044) and papillary carcinomas (P< .0001). Papillary carcinomas and atypical papillomas showed greater CK8/18 expression (and conversely less CK5 expression) than did papillomas (P < .0001). Negative or focal p63 expression was 96% sensitive for diagnosing any atypical lesion (atypical papilloma or papillary carcinoma) on excision, whereas CK8/18 predominant expression (≥80% cells) was 100% sensitive. In contrast, the sensitivity of the original diagnosis was only 81%. The greatest accuracy for the diagnosis of atypical papillary lesions (95%) was achieved when both p63 and cytokeratins were used in combination in an algorithmic fashion. This method also correctly identified all cases that had papillary carcinoma (100% sensitivity) on excision. CONCLUSIONS: Although a single stain or combination cannot independently stratify papillary lesions, a CK5/p63/CK8/18 antibody cocktail is a useful adjunct to morphology for evaluating breast papillary lesions in needle biopsy specimens.

An evaluation of the accuracy and performance of lightweight GPS collars in a suburban environment.

The recent development of lightweight GPS collars has enabled medium-to-small sized animals to be tracked via GPS telemetry. Evaluation of the performance and accuracy of GPS collars is largely confined to devices designed for large animals for deployment in natural environments. This study aimed to assess the performance of lightweight GPS collars within a suburban environment, which may be different from natural environments in a way that is relevant to satellite signal acquisition. We assessed the effects of vegetation complexity, sky availability (percentage of clear sky not obstructed by natural or artificial features of the environment), proximity to buildings, and satellite geometry on fix success rate (FSR) and location error (LE) for lightweight GPS collars within a suburban environment. Sky availability had the largest affect on FSR, while LE was influenced by sky availability, vegetation complexity, and HDOP (Horizontal Dilution of Precision). Despite the complexity and modified nature of suburban areas, values for FSR (mean= 90.6%) and LE (mean = 30.1 m) obtained within the suburban environment are comparable to those from previous evaluations of GPS collars designed for larger animals and within less built-up environments. Due to fine-scale patchiness of habitat within urban environments, it is recommended that resource selection methods that are not reliant on buffer sizes be utilised for selection studies.

Predicting summer site occupancy for an invasive species, the common brushtail possum (Trichosurus vulpecula), in an urban environment.

Invasive species are often favoured in fragmented, highly-modified, human-dominated landscapes such as urban areas. Because successful invasive urban adapters can occupy habitat that is quite different from that in their original range, effective management programmes for invasive species in urban areas require an understanding of distribution, habitat and resource requirements at a local scale that is tailored to the fine-scale heterogeneity typical of urban landscapes. The common brushtail possum (Trichosurus vulpecula) is one of New Zealand's most destructive invasive pest species. As brushtail possums traditionally occupy forest habitat, control in New Zealand has focussed on rural and forest habitats, and forest fragments in cities. However, as successful urban adapters, possums may be occupying a wider range of habitats. Here we use site occupancy methods to determine the distribution of brushtail possums across five distinguishable urban habitat types during summer, which is when possums have the greatest impacts on breeding birds. We collected data on possum presence/absence and habitat characteristics, including possible sources of supplementary food (fruit trees, vegetable gardens, compost heaps), and the availability of forest fragments from 150 survey locations. Predictive distribution models constructed using the programme PRESENCE revealed that while occupancy rates were highest in forest fragments, possums were still present across a large proportion of residential habitat with occupancy decreasing as housing density increased and green cover decreased. The presence of supplementary food sources was important in predicting possum occupancy, which may reflect the high nutritional value of these food types. Additionally, occupancy decreased as the proportion of forest fragment decreased, indicating the importance of forest fragments in determining possum distribution. Control operations to protect native birds from possum predation in cities should include well-vegetated residential areas; these modified habitats not only support possums but provide a source for reinvasion of fragments.

Nottingham-defined mitotic score: comparison with visual and image cytometric phosphohistone H3 labeling indices and correlation with Oncotype DX recurrence score.

Prognosis of breast cancer patients has been determined traditionally by lymph node status, tumor size, and histologic grade. In recent years the Oncotype DX recurrence score (RS) assay has emerged as an expensive adjunct prognostic tool. Markers of proliferation play a large role in determination of RS, and we have shown previously that immunohistochemical expression of proliferation markers Ki-67 and phosphohistone H3 (PPH3) correlates with RS. Our current goal is comparison of the hematoxylin and eosin (H&E) mitotic score, defined by the Nottingham grading system, with anti-PPH3 mitotic figure labeling assessed by both visual and automated image analysis and correlation of mitotic score results with RS. Estrogen receptor-positive breast carcinomas from 137 patients with Oncotype DX testing were selected. A representative H&E-stained tumor section was evaluated. Mitoses were counted per 10 high-power fields and tumors graded using the Nottingham criteria by 1 pathologist in accordance with College of American Pathologists-recommended mitotic count cutoffs for a field diameter of 0.55 mm. An additional section was immunostained with PPH3 antibody. PPH3 mitotic scores were determined visually and by automated imaging system. Statistical analysis was performed using univariate tests and Spearman coefficient. There was a statistically significant positive correlation among the 3 methods of mitotic score assessment. Specifically, correlation of tumor grades obtained using visual and automated methods of assessment of mitotic activity with PPH3 stain was the strongest and most statistically significant (weighted κ value 0.84, P<0.001; Spearman coefficient 0.89, P<0.001). There was a statistically significant positive correlation between H&E mitosis score and RS (P<0.001, Spearman coefficient 0.30) and between visual PPH3 mitotic score and RS (P<0.001, Spearman coefficient 0.28). In conclusion, mitotic score by any of the 3 methods studied may be useful in assessing tumor grade, proliferation, and prognosis.

GATA-3 expression in male and female breast cancers: comparison of clinicopathologic parameters and prognostic relevance.

Expression of GATA-3 in female breast cancers has been linked to estrogen receptor (ER) expression and, in turn, to improved outcomes. However, GATA-3 has not been studied in male breast cancers. Nineteen male breast carcinomas (average age: 63 years) and 164 female breast carcinomas (average age: 57 years) were immunostained for GATA-3. Results were compared to age, tumor size, tumor grade, lymph node status, distant metastases, survival, and positivity for ER, progesterone receptor (PR), and HER2/neu. Six of 19 (31.6%) male and 135 of 164 (82.3%) female breast carcinomas were GATA-3 positive (P < .001). In women, 82.1% of GATA-3-positive cancers were grade 1 or 2, whereas 75.9% of GATA-3-negative cancers were grade 3 (P < .001); no such significant correlation was seen in men. Unlike female cancers, male cancers showed no correlation between GATA-3 positivity and ER positivity, PR positivity, or distant metastases. Nodal metastasis and HER2 status were not linked to GATA-3 in either sex. Seventeen (89.5%) men were alive at follow-up (average: 61 months); only 1 died of disease. Most women (159/164, 97.0%) were also alive at follow-up (average: 41 months), with a higher proportion of GATA-3-negative women dead than GATA-3-positive women (3/29 [10.3%] vs. 2/135 [1.5%], P = .039). GATA-3 is expressed less often in male than female breast cancers. Male cancers show no correlation between GATA-3 positivity and ER/PR positivity or distant metastases, unlike female cancers. There appears to be no link between GATA-3 positivity and survival in men, whereas in women, GATA-3-positive tumors are typically lower grade with a better prognosis.

Commonly encountered dilemmas in breast cancer reporting and staging.

Treatment modalities for common malignancies such as breast carcinoma have become increasingly complex, necessitating more rigorous documentation by pathologists of the histopathologic features required for staging and therapy. In 2009 the American Joint Committee on Cancer published the most recent update to its Cancer Staging Manual, the most salient points of which are readily available on the College of American Pathologists' Web site. Based on these guidelines, herein we summarize some of the more commonly encountered dilemmas in breast cancer reporting, with emphasis on tumor size, lymph node status, determination of mitotic count for tumor grade, and skin/chest wall involvement (pathologic stage T4).

Acidophilic nuclear inclusions are specific for florid ductal hyperplasia among proliferative breast lesions.

CONTEXT: Recently we have observed distinctive acidophilic intranuclear inclusions in cases of usual intraductal hyperplasia of the breast. Similar inclusions were described almost 20 years ago in cases of mammary hyperplasia. These correlated ultrastructurally with so-called helioid inclusions. However, there since has been little discussion of these inclusions in the literature. OBJECTIVE: To examine the incidence and specificity of these inclusions in proliferative lesions of the breast. DESIGN: Forty cases of usual intraductal hyperplasia, 15 cases of atypical ductal hyperplasia, and 34 cases of low-grade ductal carcinoma in situ were examined for the presence of acidophilic intranuclear inclusions. RESULTS: Acidophilic intranuclear inclusions were present in 50% of cases of usual intraductal hyperplasia (20 of 40) but were not identified in any cases of atypical ductal hyperplasia (0 of 15) or low-grade ductal carcinoma in situ (0 of 34). CONCLUSIONS: Acidophilic intranuclear inclusions appear to be a common, specific feature found in usual intraductal hyperplasia and may be helpful in distinguishing it from atypical ductal hyperplasia and low-grade ductal carcinoma in situ in some cases. Elucidating the nature of these inclusions may provide insight into the pathogenesis of usual intraductal hyperplasia.

Proliferation (Ki-67 and phosphohistone H3) and oncotype DX recurrence score in estrogen receptor-positive breast cancer.

The Oncotype DX Recurrence Score (RS) is often used in lymph node-negative, estrogen receptor-positive breast cancer to refine prognosis and direct therapy. Its utility is limited by its cost, proprietary nature, and turnaround time. Markers of proliferation factor heavily into determination of RS. Our aim is to correlate expression of proliferation markers Ki-67 and phosphohistone H3 (PPH3) with RS and other prognostic indicators. Estrogen receptor-positive invasive breast carcinomas from 133 patients with Oncotype DX testing were selected. Representative tumor sections were stained with MIB1, a monoclonal antibody that reacts against Ki-67, and antibody to PPH3. Nuclear staining was quantitated through an automated imaging system. The percentage of positive cells was scored as low (<10%), intermediate (10% to 20%), or high (>20%) for Ki-67, and low (<2%), intermediate (2% to 5%), or high (>5%) for PPH3. Expression of both markers was compared with RS and clinicopathologic parameters including grade, tumor size, lymph node metastasis, and angiolymphatic invasion. Ki-67 and PPH3 expression were both significantly associated with RS (P=0.02 and P=0.027, respectively) and grade (P<0.001 and P=0.002, respectively). Ki-67 expression correlated with angiolymphatic invasion (P=0.01) but not with tumor size or lymph node metastasis; PPH3 expression showed no association with any of these 3 parameters. Expression of proliferation markers Ki-67 and PPH3 by immunohistochemistry is significantly correlated with RS and tumor grade. This observation suggests that immunohistochemical assessment of markers of proliferation may provide useful prognostic information, at lower cost than RS testing.

Breast arterial calcification: a marker of medial vascular calcification in chronic kidney disease.

BACKGROUND AND OBJECTIVES: Because previous studies have not distinguished between intimal (atherosclerotic) and medial vascular calcification, the prevalence and clinical significance of either condition in chronic or end-stage kidney disease (CKD or ESKD) are unknown. We hypothesized that breast arterial calcification (BAC) is exclusively medial and that mammography can serve as a useful marker of generalized medial calcification in CKD and ESKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Arterial calcification was identified histologically in breast tissue or visually in mammograms and radiographs of extremities from patients with CKD or ESKD. RESULTS: Medial calcification but no intimal calcification was present in all 16 specimens from patients with CKD or ESKD. In 71 women with ESKD, BAC was present on mammograms in 63% compared with 17% in women without renal insufficiency matched for age, race, and diabetes (P<0.001). Age and ESKD duration were significant, independent predictors of BAC. BAC was also present in 36% of mammograms from the same patients performed 5.5±0.7 years before the onset of ESKD (P<0.05 versus control) but in only 14% of patients with stage 3 CKD. Comparison of mammograms and extremity radiographs revealed that BAC was present in over 90% of patients with peripheral arterial calcification (PAC), and PAC was observed in less than 6% of patients without BAC. CONCLUSIONS: BAC is a specific and useful marker of medial vascular calcification in CKD, and its prevalence is markedly increased in ESKD and advanced CKD.

Luminal cytokeratin expression profiles of breast papillomas and papillary carcinomas and the utility of a cytokeratin 5/p63/cytokeratin 8/18 antibody cocktail in their distinction.

Luminal cytokeratin (CK) expression in breast papillary lesions, and its potential diagnostic utility among other markers in distinguishing between papillomas and papillary carcinomas, has not been previously evaluated. Such expression was determined in 42 papillary lesions (18 papillary carcinomas and 24 papillomas) by immunostaining with a CK5/p63/CK8/18 antibody cocktail. The mean CK8/18 intensity score and percentage of positive cells were significantly higher in papillary carcinomas (227 and 95%, respectively, vs 86 and 42% in papillomas; both P-values <0.0001), whereas the mean CK5 intensity score and percentage of positive cells were significantly lower (7 and 5%, respectively, vs 107 and 58% in papillomas; both P-values <0.0001). Half (9/18) of the papillary carcinomas expressed p63 vs all (24/24) of the papillomas (P = 0.0001). P63 expression in papillary carcinoma was always (9/9; 100%) focal/limited in nature (expression in <10% of cells), whereas focal expression was seen in only four (17%) papillomas (P<0.0001). Both differential CK (CK8/18 and CK5) expression and p63 were equally sensitive (100%) for the diagnosis of papillary carcinoma, but differential CK expression was more specific (96 vs 83%), resulting in a greater accuracy. However, the best discriminatory power in the distinction from papilloma was achieved when all three markers were used in combination, resulting in 100% sensitivity and specificity values. It is concluded that breast papillary lesions have differential CK expression profiles that, especially in combination with p63, can be useful for their stratification, potentially also in needle biopsy material, in which more accurate and reproducible characterization is needed.

Histologic grading of invasive lobular carcinoma: does use of a 2-tiered nuclear grading system improve interobserver variability?

The Nottingham histologic grade (NHG) is a prognostic marker for infiltrating ductal carcinoma. Its usefulness for invasive lobular carcinoma (ILC) has been less clear, given that 2 of the 3 parameters, tubule formation and mitotic activity, show little variation in ILC, placing much of the emphasis on nuclear grade. We have previously reported a trend for improved overall and relapse-free survival in patients with ILC of low nuclear grade, as classified by a 2-tiered nuclear grading system. Given the inherent potential for interobserver variability with any grading system, the goal of this study is to compare interobserver variability in the grading of ILC using a 2-tiered nuclear grade vs the NHG. Thirty-eight cases of ILC were graded independently by 5 pathologists using NHG criteria. Tumors were also categorized by a nuclear grading system as low grade (grade 1 nuclei) or high grade (grades 2-3 nuclei). Pairwise kappa values and interobserver agreement rates were calculated for both NHG and nuclear grade. Results were compared using the paired t test. Mean interobserver agreement rates and kappa values improved with use of the nuclear grading system as compared to NHG (83% vs 70%, 0.4738 vs 0.3228, respectively). The differences between the 2 were statistically significant. Because histologic grade has significant prognostic implications for patients with breast cancer, accurate reporting is paramount. For ILC, where use of the NHG places substantial weight on nuclear pleomorphism, a 2-tiered nuclear grading system may reduce interobserver variability yet still provide useful prognostic information.

Attenuated podoplanin staining in breast myoepithelial cells: a potential caveat in the diagnosis of lymphatic invasion.

Although podoplanin expression in breast myoepithelial (ME) cells has been reported to be readily distinguishable from that of lymphatic endothelium (LE), we recently encountered a case in which attenuated expression led to an incorrect interpretation of lymphatic invasion. This prompted us to further analyze the pattern and intensity of podoplanin expression in LE and in ME cells surrounding both non-neoplastic and neoplastic breast epithelium in 42 cases of breast carcinoma. In addition, cases with presumed lymphatic invasion (tumor cells within podoplanin-positive lymphatic-like structures) were further characterized on the basis of histologic review and results of additional endothelial (CD31 and/or CD34) and ME (p63+/-calponin) immunostains. Normal LE always displayed a strong (3+) linear podoplanin expression pattern, whereas ME cells surrounding non-neoplastic breast epithelium had a granular, branching membranous staining pattern that was either moderate (2+) or strong (3+) in 13 (34%) and 25 (66%) foci, respectively. ME cells surrounding ductal carcinoma in situ (DCIS) displayed weaker (1+ to 2+) podoplanin expression with 26 (72%) foci showing only a residual thin/discontinuous pattern of expression, whereas the other 10 (28%) foci showed a pattern similar to that around non-neoplastic epithelium. Further evaluation of 10 foci of presumed lymphatic invasion confirmed the presence of lymphatic invasion in 6 (60%) cases, whereas 4 displayed surrounding ME cells and were thus interpreted as DCIS. One case, in which both DCIS and lymphatic invasion were unequivocally present, displayed a few nests of tumor cells surrounded by both podoplanin-positive and p63-positive cells in different areas of the periphery and could not be readily classified. These findings represent an important caveat in the diagnosis of lymphatic invasion and, accordingly, one should always interpret results of podoplanin staining in the context of the histologic appearance and/or consider evaluation of additional endothelial or ME immunostains, especially when the characteristically strong linear pattern of expression of LE is not evident.

Effect of storage on p63 immunohistochemistry: a time-course study.

One of the problems with immunohistochemistry is that storage of unstained slides can have a detectable negative effect on the intensity of staining for various antigens. This has not been well studied for the p63 antigen. A time-course study was performed to evaluate the effect of storage on the intensity of p63 immunohistochemical staining. Slides from various breast lesions/foci were stained with a p63 antibody on day 0 and after storage at room temperature for 2, 4, and 8 weeks. A p63 intensity score, ranging from 0 to 300, was calculated using the intensity (0, 1, 2, or 3+) and percentage of peripheral myoepithelial cell staining (0% to 100%). There was a progressive decline in the p63 intensity score with time with the differences between day 0 and 2 weeks and 2 and 4 weeks being statistically significant (P=0.037 and 0.001, respectively), whereas that between 4 and 8 weeks was not (P=0.075). These findings confirm a time-dependent decline in p63 immunostaining intensity evident as early as with 2 weeks of storage and still present after 8 weeks. This should be considered in the evaluation of p63 immunostains performed on stored unstained sections, both in diagnostic surgical pathology and in translational research studies.

Using a higher cutoff for the percentage of HER2+ cells decreases interobserver variability in the interpretation of HER2 immunohistochemical analysis.

The effect of using a 30% cutoff for the proportion of HER2+ cells on the interobserver variability in the interpretation of HER2 immunohistochemical results was evaluated. Immunostained sections from 96 cases of breast carcinoma were reviewed by 10 pathologists and scored as positive (3+) when uniform strong membranous staining was identified in at least 10% of tumor cells; the actual percentage of cells with such staining was also estimated. The agreement rates and the kappa values using a 30% cutoff were compared with those using a 10% cutoff. These proved to be higher in 62% and 66% of measurements, respectively, with average interobserver rates and kappa values of 72% and 0.54 using the 30% cutoff and 70% and 0.49 using the 10% cutoff (P=.001 for all comparisons). Using a 30% cutoff for the percentage of HER2+ cells by immunohistochemical analysis modestly decreased interobserver variability in the interpretation of HER2 immunohistochemical results.