CONTEXT.—: The use of immunohistochemical stains in breast and gynecologic pathology has become increasingly complex, with various diagnostic, prognostic, and predictive applications. OBJECTIVE.—: To provide an update and review of immunohistochemical stains used in the practice of breast and gynecologic pathology. Established and new entities are reviewed, with descriptions of histomorphology and immunohistochemical staining patterns and discussion of interpretive pitfalls. DATA SOURCES.—: Data were obtained from review of the English-language literature and firsthand experience of the authors in breast and gynecologic pathology. CONCLUSIONS.—: Many entities in breast and gynecologic pathology benefit from evaluation with various immunohistochemical stains. These studies not only aid in the diagnosis and staging of tumors but also can provide prognostic and predictive information. Updated guidelines for recommended ancillary studies such as mismatch repair, p53, and human epidermal growth factor receptor 2 (HER2) studies in endometrium, as well as estrogen and progesterone receptors and HER2 in breast, are discussed. Finally, the use and interpretation of established and novel immunohistochemical stains are discussed in various breast and gynecologic malignancies.

CONTEXT.—: Immunohistochemistry has become a valuable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels. OBJECTIVE.—: To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry. DATA SOURCES.—: Literature review and the author's research data and personal practice experience. CONCLUSIONS.—: This review article highlights that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoid potential diagnostic errors.

CONTEXT.—: Two major categories of laboratories performing nonwaived testing under the Clinical Laboratory Improvement Amendments of 1988 (CLIA) are the Certificate of Accreditation (CoA) and Certificate of Compliance (CoC) laboratories. Accreditation organizations collect more detailed laboratory personnel information than the Centers for Medicare & Medicaid Services (CMS) Quality Improvement and Evaluation System (QIES). OBJECTIVE.—: To estimate total numbers of testing personnel and testing volumes in CoA and CoC laboratories, by laboratory type and state. DESIGN.—: We developed a statistical inference method by using the respective correlations between testing personnel counts and test volume by laboratory type. RESULTS.—: QIES reported 33 033 active CoA and CoC laboratories in July 2021. We estimated testing personnel to be 328 000 (95% CI, 309 000-348 000), which is supported by the count of 318 780 reported by the US Bureau of Labor Statistics. There were twice as many testing personnel in hospital laboratories as in independent laboratories (158 778 versus 74 904, P < .001). Independent laboratories had the highest test volume per person, which was twice as high as physician office laboratories (62 228 versus 30 102, P < .001). Hospital and independent laboratories comprised 34% of all CoA and CoC laboratories but performed the largest portion of testing (81%). Physician office laboratories, accounting for 44% of all CoA and CoC laboratories, performed a comparatively low proportion of total tests (9%). CONCLUSIONS.—: Numbers of testing personnel vary considerably by laboratory type and across states. These data can provide valuable insight when assessing laboratory workforce training needs and planning for public health emergencies.

CONTEXT.—: Definitive diagnosis of metastatic triple-negative breast carcinoma (TNBC) is challenging on cytologic samples. Recent studies demonstrated that trichorhinophalangeal syndrome type 1 (TRPS1) is a highly sensitive and specific marker for diagnosing breast carcinomas, including TNBC, on surgical specimens. OBJECTIVE.—: To evaluate TRPS1 expression in TNBCs on cytologic samples and a large series of nonbreast tumors on tissue microarray sections. DESIGN.—: Immunohistochemical (IHC) analysis of TRPS1 and GATA-binding protein 3 (GATA3) was performed on 35 TNBC cases on surgical specimens, and 29 consecutive TNBC cases on cytologic specimens. IHC analysis of TRPS1 expression was also performed on 1079 nonbreast tumors on tissue microarray sections. RESULTS.—: Of the surgical specimens, 35 of 35 TNBC cases (100%) were positive for TRPS1, all with diffuse positivity, whereas 27 of 35 (77%) were positive for GATA3, with diffuse positivity in 7 cases (26%). Of the cytologic samples, 27 of 29 TNBC cases (93%) were positive for TRPS1, with diffuse positivity in 20 cases (74%), whereas 12 of 29 (41%) were positive for GATA3, with diffuse positivity in 2 cases (17%). Of the nonbreast malignant tumors, TRPS1 expression was seen in 9.4% (3 of 32) of melanomas, 10.7% (3 of 28) of small cell carcinomas of the bladder, and 9.7% (4 of 41) of ovarian serous carcinomas. CONCLUSIONS.—: Our data confirm that TRPS1 is a highly sensitive and specific marker for diagnosing TNBC cases on surgical specimens as reported in the literature. In addition, these data demonstrate that TRPS1 is a much more sensitive marker than GATA3 in detecting metastatic TNBC cases on cytologic samples. Therefore, inclusion of TRPS1 in the diagnostic IHC panel is recommended when a metastatic TNBC is suspected.

CONTEXT: Unlike B-cell acute lymphoblastic leukemia/lymphoma (ALL/LBL), there have been few therapeutic advances in T-cell ALL/LBL, an aggressive ALL/LBL subtype. OBJECTIVE: To perform a focused tissue array study to elucidate tumor markers of therapeutic potential in T-ALL/LBL. DESIGN: Using immunohistochemistry, we evaluated expression of leukemic antigens of interest, specifically CC-Chemokine receptor 4 (CCR4), among others, on available remnant diagnostic material, including tumor tissue slides obtained from formalin-fixed, paraffin-embedded preserved tissues. RESULTS: Our analysis identified for the first time expression of CCR4 in T-ALL/LBL in 11 of 27 cases (40.7%) and confirmed common expression of BCL2, CD38, and CD47, as reported previously. We also identified the expression of CD123 in 4 of 26 cases (15.4%), whereas BCL6 and PDL1 were expressed in a small number of T-ALL/LBL cases. The potential novel target CCR4 was significantly more common in the Pre/Pro-T immunophenotypic (IP) subtype, 6 of 9 (66.7%, P = .011). No additional differences in clinical and epidemiologic variables were noted among positive or negative CCR4 cases. CONCLUSIONS: These findings support preclinical and clinical testing of therapies targeting CCR4, CD47, BCL2, CD38, and CD123 in T-ALL/LBL, and may help guide the development of targeted clinical trials in T-cell ALL/LBL, a rare disease in urgent need of novel therapies.

CONTEXT: In the clinical practice of breast pathology, immunohistochemistry (IHC) of different markers is widely used for the diagnosis and classification of breast lesions. OBJECTIVE: To provide an overview of currently used and recently identified IHC stains that have been implemented in the field of diagnostic breast pathology. DATA SOURCES: Data were obtained from literature review and clinical experience of the authors as breast pathologists. CONCLUSIONS: In the current review, we summarize the common uses of IHC stains for diagnosing different types of breast lesions, especially invasive and noninvasive breast lesions, and benign and malignant spindle cell lesions. In addition, the cutting-edge knowledge of diagnostic carcinoma markers will lead us to further understand the different types of breast carcinoma and differentiate breast carcinomas from other carcinomas of similar morphology. Knowing the strengths and limitations of these markers is essential for the clinical practice of breast pathology.

CONTEXT: Human epidermal growth factor (HER2/neu) gene amplification, a poor prognostic factor in invasive breast cancer, has shown substantial utility as a predictive marker, with significantly improved survival following anti-HER2 therapies like trastuzumab. Dual-color dual in situ hybridization (D-DISH), a recently introduced fully automated assay for HER2/neu evaluation on light microscopy, has several advantages over fluorescence in situ hybridization (FISH). OBJECTIVE: To standardize and validate the D-DISH assay using FISH as the gold standard and assess interobserver reproducibility in interpreting the D-DISH assay. DESIGN: D-DISH was performed using the latest HER2 Dual ISH DNA Probe Cocktail assay (Ventana Medical Systems Inc, Tucson, Arizona) in 148 cases of invasive breast cancer. The same block was used for performing immunohistochemistry by Ventana PATHWAY anti-HER2/neu (4B5) antibody and FISH assay by ZytoLight SPEC ERBB2/CEN17 Dual Color Probe. D-DISH was separately interpreted by 4 pathologists blinded to FISH results. RESULTS: Concordance of 98.65% and a Cohen κ value of 0.97 were observed between FISH and D-DISH. Intraclass correlation coefficient (0.93-0.97) and κ values (0.98-1.0) for interobserver reproducibility showed almost perfect agreement by D-DISH. Interobserver reproducibility was also evaluated for genomic heterogeneity, HER2 group categorization, and polysomy (κ values 0.42-0.74, 0.89-0.93, and 0.98-1.0, respectively). CONCLUSIONS: We successfully validated the latest version of D-DISH assay as a substitute for FISH in predicting HER2 gene status with significant interobserver reproducibility, concluding that this D-DISH assay may be introduced in routine diagnostic services as a reflex test to ascertain HER2 gene status.

CONTEXT: Chronic histiocytic intervillositis (CHI) is a rare condition characterized by maternal immune cell infiltration into the human placenta. CHI is strongly associated with fetal growth restriction, miscarriage, and stillbirth, and knowledge of its etiology, and consequently effective treatment, is limited. Currently, diagnosis is largely subjective and varies between centers, making comparison between studies challenging. OBJECTIVE: To objectively quantify and interrelate inflammatory cells and fibrin in placentas with CHI compared with controls and determine how pathology may be altered in subsequent pregnancies following diagnosis. Macrophage phenotype was also investigated in untreated cases of CHI. DESIGN: Computerized analysis was applied to immunohistochemically stained untreated (index) cases of CHI, subsequent pregnancies, and controls. Index placentas were additionally stained by immunofluorescence for M1 (CD80 and CD86) and M2 macrophage markers (CD163 and CD206). RESULTS: Quantification revealed a median 32-fold increase in macrophage infiltration in index cases versus controls, with CHI recurring in 2 of 11 (18.2%) subsequent pregnancies. A total of 4 of 14 placentas (28.6%) with a diagnosis of CHI did not exhibit infiltration above controls. Macrophages in index pregnancies strongly expressed CD163. There was no significant difference in fibrin deposition between index cases and controls, although subsequent pregnancies displayed a 2-fold decrease compared with index pregnancies. CD3+ T cells were significantly elevated in index pregnancies; however, they returned to normal levels in subsequent pregnancies. CONCLUSIONS: In CHI, intervillous macrophages expressed CD163, possibly representing an attempt to resolve inflammation. Computerized analysis of inflammation in CHI may be useful in determining how treatment affects recurrence, and alongside pathologist expertise in grading lesion severity.

CONTEXT.—: Mast cells are essential components of the immune system and play crucial pathogenetic roles in several digestive diseases, including mastocytic enterocolitis and eosinophilic gastrointestinal disorders. Pathologists have rarely been asked to evaluate the distribution and density of mast cells in gastrointestinal (GI) biopsy specimens. However, such requests are becoming more common because of an increasing awareness of the role of mast cells in functional GI disease and in both esophageal and nonesophageal eosinophilic gastrointestinal disorders. OBJECTIVE.—: To provide pathologists with tools to incorporate the assessment of mast cells in the evaluation of esophageal, gastric, and intestinal specimens by developing a systematic approach to their evaluation, counting, and reporting. DESIGN.—: The study consists of a review of the literature followed by multiple consensus sessions to decide where to count mast cells and what a countable mast cell is. RESULTS.—: We reviewed 135 papers addressing the content of mast cells in the digestive tract, selected 21 that detailed how cells were counted (microscope lens, area of high-power fields, locations evaluated, type of cells considered as countable), and summarized their data in a table. Then, drawing from both the acceptable literature and our own extensive experience, we reached a tentative consensus on: (1) the normal numbers in the different segments of the GI tract; (2) the morphology of countable mast cells; and (3) the locations and strategies for counting them. CONCLUSIONS.—: The result is a set of suggestions for reporting mast cell counts, distribution, and location in a way clinicians can understand and use for management decisions.

CONTEXT.—: The year 2023 marks the centenary of the Nobel Prize honoring the discovery of insulin. Little-known experimental pathologists Lydia DeWitt, MD, at the University of Michigan and Mary Kirkbride, DSc [Hon], at Columbia University, both just beginning their academic careers, made independent contributions to the discovery that have never been critically examined. This happened at a time when women in pathology were exceedingly rare. OBJECTIVE.—: To explore the facilitative roles of DeWitt and Kirkbride in the discovery and to examine their trail-breaking careers in academic pathology. DESIGN.—: Available primary and secondary historical resources were reviewed. RESULTS.—: DeWitt made and tested pancreatic extracts from duct-ligated atrophic pancreas (ie, Frederick Banting's great idea to prevent digestion of its hypothetical internal secretion) 15 years before Banting; Banting was unaware of her work. His idea came from reading a paper by pathologist Moses Barron. Prior duct-ligation studies had sometimes been viewed with skepticism because histologic identification of islets in atrophic duct-ligated pancreata was imperfect; Kirkbride addressed this with histochemical staining, convincing Barron and, therefore, indirectly influencing and motivating Banting. The lives and convoluted careers of these 2 early-20th-century women are explored and compared with those of other contemporary women in pathology. A unifying pattern becomes clear: careers in experimental pathology and bacteriology were accepted but performing clinical work in anatomic pathology was not. CONCLUSIONS.—: Both DeWitt and Kirkbride are prototypical early-20th-century women in academic pathology whose careers were constrained by gender. However, Kirkbride made a unique and unrecognized contribution to the discovery of insulin.

CONTEXT.—: Before its eradication, the smallpox virus was a significant cause of poor obstetric outcomes, including maternal and fetal morbidity and mortality. The mpox (monkeypox) virus is now the most pathogenic member of the Orthopoxvirus genus infecting humans. The 2022 global mpox outbreak has focused attention on its potential effects during pregnancy. OBJECTIVE.—: To understand the comparative effects of different poxvirus infections on pregnancy, including mpox virus, variola virus, vaccinia virus, and cowpox virus. The impact on the pregnant individual, fetus, and placenta will be examined, with particular attention to the occurrence of intrauterine vertical transmission and congenital infection. DATA SOURCES.—: The data are obtained from the authors' cases and from various published sources, including early historical information and contemporary publications. CONCLUSIONS.—: Smallpox caused maternal and perinatal death, with numerous cases reported of intrauterine transmission. In endemic African countries, mpox has also affected pregnant individuals, with up to a 75% perinatal case fatality rate. Since the start of the 2022 mpox outbreak, increasing numbers of pregnant women have been infected with the virus. A detailed description is given of the congenital mpox syndrome in a stillborn fetus, resulting from maternal-fetal transmission and placental infection, and the potential mechanisms of intrauterine infection are discussed. Other poxviruses, notably vaccinia virus and, in 1 case, cowpox virus, can also cause perinatal infection. Based on the historical evidence of poxvirus infections, mpox remains a threat to the pregnant population, and it can be expected that additional cases will occur in the future.