Multi-institutional Assessment of Pathologist Scoring HER2 Immunohistochemistry

The HercepTest was approved 20+ years ago as the companion diagnostic test for trastuzumab in human epidermal growth factor 2 (HER2) or ERBB2 gene-amplified/overexpressing breast cancers. Subsequent HER2 immunohistochemistry (IHC) assays followed, including the now most common Ventana 4B5 assay. Although this IHC assay has become the clinical standard, its reliability, reproducibility, and accuracy have largely been approved and accepted on the basis of concordance among small numbers of pathologists without validation in a real-world setting. In this study, we evaluated the concordance and interrater reliability of scoring HER2 IHC in 170 breast cancer biopsies by 18 breast cancer-specialized pathologists from 15 institutions. We used the Observers Needed to Evaluate Subjective Tests method to determine the plateau of concordance and the minimum number of pathologists needed to estimate interrater agreement values for large numbers of raters, as seen in the real-world setting. We report substantial discordance within the intermediate categories (<1% agreement for 1+ and 3.6% agreement for 2+) in the 4-category HER2 IHC scoring system. The discordance within the IHC 0 cases is also substantial with an overall percent agreement (OPA) of only 25% and poor interrater reliability metrics (0.49 Fleiss' kappa, 0.55 intraclass correlation coefficient). This discordance can be partially reduced by using a 3-category system (28.8% vs 46.5% OPA for 4-category and 3-category scoring systems, respectively). Observers Needed to Evaluate Subjective Tests plots suggest that the OPA for the task of determining a HER2 IHC score 0 from not 0 plateaus statistically around 59.4% at 10 raters. Conversely, at the task of scoring HER2 IHC as 3+ or not 3+ pathologists' concordance was much higher with an OPA that plateaus at 87.1% with 6 raters. This suggests that legacy HER2 IHC remains valuable for finding the patients in whom the ERBB2 gene is amplified but unacceptably discordant in assigning HER2-low or HER2-negative status for the emerging HER2-low therapies.

Examination of Low ERBB2 Protein Expression in Breast Cancer Tissue

IMPORTANCE

Trastuzumab deruxtecan (T-DXd) has shown efficacy in patients with breast cancer with ERBB2 immunohistochemistry (IHC) scores of 1+ or 2+ but not 0 as read in central pathology laboratories. The drug is currently being tested in large randomized clinical trials with registration intent for this patient population.

OBJECTIVE

To determine the suitability of the current standard ERBB2 IHC assays to select patients with low ERBB2 positivity for treatment with T-DXd.

DESIGN AND SETTING

Assessment of data from College of American Pathologists surveys and assessment of analytic data from a Yale University-based study of concordance of 18 pathologists reading 170 breast cancer biopsies.

RESULTS

The total survey data set included scores over 2 years from 1391 to 1452 laboratories of 40 ERBB2 cores from each laboratory (20 cores twice a year for a total of 80). College of American Pathologists surveys show that 19% of cases read by the laboratories generate results with less than or equal to 70% concordance for IHC ERBB2 score 0 vs 1+. When 18 pathologists read the scanned slides from a selected set of breast cancer biopsies using a 4-point scale, there was only 26% concordance between 0 and 1+ compared with 58% concordance between 2+ and 3+.

CONCLUSIONS AND RELEVANCE

In this study using a current standard ERBB2 IHC assay, the scoring accuracy for ERBB2 IHC in the low range (0 and 1+) was poor. This inaccuracy in the real world could lead to misassignment of many patients for treatment with T-DXd.

Abstract P1-02-02: Examination of low Her2 expression in breast cancer

Introduction: Antibody-drug conjugates (ADC) are designed to effectively deliver cytotoxic agents directly to malignant cells. Trastuzumab deruxtecan (Tdx), an ADC of trastuzumab, an enzyme-cleavable linker, and a cytotoxic topoisomerase I inhibitor, has been shown to have antitumor activity in patients with breast cancer with low levels of HER2. However, current companion diagnostic tests for HER2-targetting therapies, immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH), were optimized for high (gene amplified) levels of HER2. We hypothesize that the current common assays used in clinic do not efficiently differentiate between patients whose cancers have “0” HER2 expression and “1+” HER2 expression and thus could miss patients who would benefit from treatment with this drug. Methods: Here, we evaluated two years of HER2 surveys from the College of American Pathologists’ (CAP) Proficiency Testing Surveys for HER2 expression in breast cancer from 2019 and 2020. Participating laboratories received two tissue microarrays (TMAs) of 10 breast cancer cores, each Laboratories stained for HER2 using the standard IHC assay used in their labs. The scores were returned to the CAP as part of their quality assessment program. Each survey dataset covers the scores from around 1400 labs of 20 cores each as well as supplemental questions regarding the methodology used. We summarized the relative frequency and distribution of each score given to every core. A second independent analytic dataset was selected from the archives of the Department of Pathology at Yale, from breast biopsies in 2018. The set, enriched in HER2 2+ and 3+ cases, was read by eighteen board-certified pathologists, most with over 5 years’ experience, participating in an interobserver variability study. Hematoxylin and eosin (H&E) and HER2 IHC digitally scanned images of 170 independent cases were provided. Pathologists scored the cases as 0,1, 2, or 3+. Fisher’s exact test was used to compare the 0/1+ concordant cases to 2+/3+ cases. All tests were two-sided at a significant level 0.05. Statistical analysis was performed using Graphpad Prism Version 9.0.1 and the dplyr package in R Version 1.0.143. This study was approved by Yale Human Investigation IRB protocol ID 9505008219. Results: We found that 65% of the 80 cores evaluated in the CAP survey (52/80) had a concordance rate ≥90%. This high concordance was limited to scores of 0 and 3+. The lowest concordance was found between 0 versus 1+. Of the 80 cores, 56 were considered negative (HER2 score of 0 or 1). In 25% of those cores there was &lt; 70% concordance (n=15; 6 in 2019 and 9 in 2020). Analytic concordance was assessed in the independent, Yale cohort where we found that of the 170 cases, 92 were read as 0 by at least one pathologist. Of these 92, 24 were concordant (26%), defined as a ≥90% agreement. In comparison, 45/170 were read as 3+ by at least one pathologist. Again,. using a 90%definition of concordance, 26 of 45 cases (58%) were concordant. Comparison of 0/1+ concordant cases versus 2+/3+ concordant cases showed a significant difference (χ2 = 12.07, p&lt;0.0005). Conclusions: Assessment of laboratory performance of around 1400 CAP labs using common current HER2 assays on CAP survey specimens, there is significant discordance in the evaluation of 0 vs. 1+ cases. In a separate selected breast biopsy cohort examined by 18 breast pathologists, we showed that discordance between scores of 0 vs 1+ is significantly larger than that between 2+ and 3+. Given the efficacy of T-DXd, we believe patients may be mis-assigned for treatment or no treatment if the decision depends on performance of the standard current HER2 assays.

Citation Format: Aileen I Fernandez, Matthew Liu, Andrew Bellizzi, Jane Brock, Oluwole Fadare, Krisztina Hanley, Malini Harigopal, Julie M. Jorns, M. Gabriela Kuba, Amy Ly, Mirna Podoll, Kimmie Rabe, Mary Ann Sanders, Kamaljeet Singh, Olivia L Snir, Rinda Soong, Shi Wei, Hannah Wen, Serena Wong, Esther Yoon, Lajos Pusztai, Emily Reisenbichler, David L. Rimm. Examination of low Her2 expression in breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-02-02.

One Hundred Years of the Pathology Medical Student Fellowship

CONTEXT.—

The Pathology Medical Student Fellowship (PSF) is a unique, year-long immersive educational experience. Review of institutional archives describes a medical student "Fellowship in Pathology" founded in 1919.

OBJECTIVE.—

To characterize the impacts of this 100-year-old program.

DESIGN.—

We determined subsequent medical specialty of each PSF graduate in our department and surveyed those with available contact information.

RESULTS.—

Of 145 pathology student fellows graduating between 1924 and 2020, a total of 50 (34.4%) matched into pathology; medical, surgical, and radiology subspecialties were also well-represented career choices. Between 2001 and 2020, of 36 students who matched into pathology from our institution, 19 (52.8%) had completed the fellowship. Survey respondents (n = 42) indicated that before the PSF, 11 of 42 students (26.2 %) were undecided in specialty, with only 6 (14.3%) identifying pathology as their primary field of interest. Of survey respondents who had completed training, 26 (61.9%) practice in academic settings. Nonpathology physicians reported frequent utilization of skills gained during the PSF year, with 5 of 23 (21.7%) responding "daily," and 9 (39.1%) responding "weekly." The most useful skills included knowledge of pathophysiology of disease and anatomy, improved communication with multidisciplinary teams, and/or interpretation of pathology results (each selected by 17 to 20 students, 73.9%-87.0%). Free-text responses on impacts of the PSF described enhanced knowledge of disease pathobiology and diagnostic complexity and increased confidence and autonomy.

CONCLUSIONS.—

We describe the program structure, educational benefits, graduate specialty choices, and career impacts of 100 years of the PSF at our institution. Although undecided before pathology exposure, many PSF graduates subsequently enter pathology careers. Regardless of specialty choice, PSF graduates have a high rate of subsequently pursuing academic medical careers.

Silicone granuloma mimicking Breast Implant Associated Large Cell Lymphoma (BIA-ALCL): a case report

We describe the case of a 75-year-old woman with textured silicone implants who was referred to our institution with concern for implant rupture and Breast Implant Associated Anaplastic Large Cell Lymphoma (BIA-ALCL). After explantation and pathologic evaluation, she was diagnosed with silicone granuloma and adenitis, though her presentation mimicked BIA-ALCL.

HER2 testing of gynecologic carcinosarcomas: tumor stratification for potential targeted therapy

A recent phase II clinical trial showed increased progression-free survival in patients with HER2-positive endometrial serous carcinoma receiving trastuzumab in addition to carboplatin-paclitaxel chemotherapy. Similar to endometrial serous carcinomas, carcinosarcomas of the female genital tract have a dismal prognosis and could potentially benefit from new targeted therapeutic approaches. We aimed to systematically evaluate the characteristics of HER2 expression/amplification in gynecologic carcinosarcomas using standardized staining methods and scoring criteria. Tumors from 80 patients (65 uterine, 15 tubo-ovarian) were included, containing a serous (60%), endometrioid (10%), clear cell (3%), undifferentiated (3%), neuroendocrine (1%), or mixed (24%) carcinoma, and either a homologous (46%), or a heterologous (54%) sarcoma component. HER2 scores were assigned to both components per the 2007 and 2013 ASCO/CAP breast scoring criteria. A total of 13 cases (12 uterine, 1 ovarian, 16%) were HER2 positive (either by immunohistochemistry or FISH) using the 2013 criteria, while only 10 cases (9 uterine, 1 ovarian, 13%) were HER2 positive per the 2007 criteria. Nine cases showed a change in their HER2 immunohistochemical score between the two scoring systems, including two cases with a change in the overall HER2 status from negative (2007) to positive (2013). Heterogeneity of HER2 protein expression was observed in 38% of HER2-positive tumors, and a lateral/basolateral membranous staining pattern was common. The sarcoma component showed 2+, equivocal HER2 expression in five cases, one of which also demonstrated HER2 amplification by FISH. All HER2-positive carcinosarcomas had either a serous or a mixed carcinoma component, and all but one HER2-positive tumors were of uterine primaries. Our study demonstrates that gynecologic carcinosarcomas share similarities in their HER2 expression/amplification profiles to endometrial serous carcinomas, which should be taken into account when assessing their HER2 status to ensure appropriate patient selection for potential targeted HER2-based therapies in the future.

Interobserver variability in breast carcinoma grading results in prognostic stage differences

The AJCC Cancer Staging Manual 8th edition included tumor grade in the pathologic prognostic stage for breast carcinomas. Due to the known subjectivity of tumor grading, we aimed to assess the degree of interobserver agreement for invasive carcinoma grade among pathologists and determine its effect on pathologic prognostic stage. One hundred consecutive cases of invasive stage II carcinomas were independently graded twice, with an 4-week intervening wash-out period, by 6 breast pathologists utilizing established Nottingham grading criteria. Inter- and intra-observer variability was determined for overall grade and for each of the 3 scoring components. Interobserver variability was good to very good (κ range = 0.582-0.850) with even better intra-observer variability (mean κ = 0.766). Tubule score was the most reproducible element (κ = 0.588). Complete concordance was reached in 54 cases and 58 cases in rounds 1 and 2 respectively. In round 1 this resulted in different pathologic prognostic stage in only 25 of discordant cases, 18 of which were stage IA versus IB. In conclusion, grading agreement between pathologists was good to very good and discordant grades resulted in small changes to pathologic prognostic stage.

Frequent homozygosity in both mature and immature ovarian teratomas: a shared genetic basis of tumorigenesis

Although homozygosity is well documented in mature teratomas, the genetic zygosity of ovarian immature teratomas and mixed germ cell tumors is less well studied. Ten cases of mature cystic teratomas, eleven cases of grade 2 or 3 immature teratomas, and seven cases of mixed germ cell tumors with an immature teratoma component were investigated by short tandem repeat genotyping to interrogate their genetic zygosity. DNA genotyping was informative in eight mature teratomas, seven immature teratomas and six cases of mixed germ cell tumors. Out of the eight mature teratomas, five cases showed partial or complete homozygosity (63%) with two cases demonstrating complete homozygosity (25%). Of the immature teratomas, six cases showed partial or complete homozygosity (86%) with two cases demonstrating complete homozygosity (29%). For the mixed germ cell tumors, two cases showed partial homozygosity (33%) and none displayed complete homozygosity. Long-term clinical follow-up was available for five immature teratomas (mean follow-up 110 months) and five mixed germ cell tumors (mean follow-up 66 months). None of the five patients with pure immature teratoma had a recurrence; in contrast, four out of five mixed ovarian germ cell tumors recurred between 4 months to 8 years (P=0.048). In conclusion, both immature and mature teratomas harbor frequent genetic homozygosity suggesting a common cellular origin involving germ cells at the same developmental stage. The difference in the rate of homozygosity and tumor recurrence between pure immature teratomas and mixed germ cell tumors suggests that the two entities may involve different pathogenetic pathways and likely pursue different biological behaviors.

BLOC-2 targets recycling endosomal tubules to melanosomes for cargo delivery

Quantitative analyses of melanosome cargo localization and trafficking and of endosomal membrane dynamics in immortalized melanocytes from mouse Hermansky–Pudlak syndrome models show that BLOC-2 functions to specify the delivery of recycling endosomal cargo transport intermediates to maturing melanosomes.

Hermansky–Pudlak syndrome (HPS) is a group of disorders characterized by the malformation of lysosome-related organelles, such as pigment cell melanosomes. Three of nine characterized HPS subtypes result from mutations in subunits of BLOC-2, a protein complex with no known molecular function. In this paper, we exploit melanocytes from mouse HPS models to place BLOC-2 within a cargo transport pathway from recycling endosomal domains to maturing melanosomes. In BLOC-2–deficient melanocytes, the melanosomal protein TYRP1 was largely depleted from pigment granules and underwent accelerated recycling from endosomes to the plasma membrane and to the Golgi. By live-cell imaging, recycling endosomal tubules of wild-type melanocytes made frequent and prolonged contacts with maturing melanosomes; in contrast, tubules from BLOC-2–deficient cells were shorter in length and made fewer, more transient contacts with melanosomes. These results support a model in which BLOC-2 functions to direct recycling endosomal tubular transport intermediates to maturing melanosomes and thereby promote cargo delivery and optimal pigmentation.