CONTEXT.—: Pathologists can greatly improve patient care and advance the understanding of disease progression by adeptly employing relevant biomarkers when diagnosing myeloid neoplasms. Although the molecular era has ushered in countless molecular biomarkers in this field, the necessary techniques can be expensive and time-consuming. Novel immunohistochemical biomarkers can help to quickly and inexpensively render the correct diagnosis and predict response to targeted therapies. Hence, it is critical to continue studying and using new and promising immunohistochemical tools for myeloid neoplasms in our current era. OBJECTIVE.—: To review the emerging biomarkers in myeloid neoplasms that can be identified by immunohistochemistry and to discuss their utility, staining patterns, and pitfalls. DATA SOURCES.—: We conducted a scientific literature search of articles related to either a novel immunohistochemical marker or a new utility of an already known marker to assess myeloid neoplasms in PubMed from 2016 to September 30, 2021. We curated relevant contributing studies from the references and subsequent citations of the original articles. CONCLUSIONS.—: Immunohistochemistry is a powerful tool in analyzing biomarkers that play a significant role in management of patients with myeloid neoplasms. We reviewed 5 immunohistochemical markers, namely, IDH1R132H, ERG, IRF8, GATA1, and NPM1. These markers, depending on the clinical scenario, can be diagnostic, predictive, and also prognostic. Immunohistochemistry also empowers us to evaluate these markers in archival samples, including pretreatment and posttreatment biopsies.

CONTEXT.—: Endometrial serous carcinoma is well known for its high risk of extrauterine spread, even when the intrauterine tumor is minimal in volume and limited to the endometrium. Representing the earliest recognizable forms of endometrial serous carcinoma, minimal uterine serous carcinoma (MUSC) includes serous endometrial intraepithelial carcinoma and superficial serous carcinoma. OBJECTIVE.—: To discuss the pathogenetic relationship between MUSC and endometrial polyp, and to review the pathologic diagnosis and clinical implication of MUSC. DATA SOURCES.—: Sources are a literature review and the author's personal practice and prospective. CONCLUSIONS.—: A close topographic relationship between MUSC and endometrial polyp has been consistently observed in many studies: more than two-thirds of MUSCs involve an endometrial polyp and >50% of MUSCs are confined to an endometrial polyp at time of staging hysterectomy, indicating that most if not all MUSCs arise in an endometrial polyp. Timely diagnostic recognition of MUSC is clinically critical because the patients without extrauterine tumor spread have an excellent prognosis and those with extrauterine involvement have a dismal outcome. Further investigations into the endometrial polyp harboring MUSC may elucidate the key cellular and molecular alterations underpinning the pathogenesis of uterine serous carcinoma.

CONTEXT.—: The most common benign hepatic mass-forming lesions often display fairly specific imaging characteristics, whereas less familiar, rarer benign neoplasms and pseudotumors may pose a diagnostic challenge in clinical, radiology, and pathology practice because of either their rarity or their unusual features. OBJECTIVE.—: To review a selection of pseudotumors and unusual benign hepatic neoplasms encountered in consultation practices with a focus on nonepithelial tumors. DATA SOURCES.—: Sources include English-language literature and personal experiences. CONCLUSIONS.—: Several benign conditions (namely, segmental atrophy, infections, immunoglobulin G4 [IgG4]-related sclerosing disease, angiomyolipoma, mesenchymal hamartoma, and various vascular lesions) can lead to formation of hepatic masses. Because of their rarity and underrecognition, such lesions are often diagnostically challenging. Awareness of hepatic pseudotumors and various rare hepatic neoplasms and their potential mimics can forestall misdiagnosis and inappropriate management.

CONTEXT.—: The diagnosis and clinical management of patients with diffuse gliomas (DGs) have evolved rapidly over the past decade with the emergence of molecular biomarkers that are used to classify, stratify risk, and predict treatment response for optimal clinical care. OBJECTIVE.—: To develop evidence-based recommendations for informing molecular biomarker testing for pediatric and adult patients with DGs and provide guidance for appropriate laboratory test and biomarker selection for optimal diagnosis, risk stratification, and prediction. DESIGN.—: The College of American Pathologists convened an expert panel to perform a systematic review of the literature and develop recommendations. A systematic review of literature was conducted to address the overarching question, "What ancillary tests are needed to classify DGs and sufficiently inform the clinical management of patients?" Recommendations were derived from quality of evidence, open comment feedback, and expert panel consensus. RESULTS.—: Thirteen recommendations and 3 good practice statements were established to guide pathologists and treating physicians on the most appropriate methods and molecular biomarkers to include in laboratory testing to inform clinical management of patients with DGs. CONCLUSIONS.—: Evidence-based incorporation of laboratory results from molecular biomarker testing into integrated diagnoses of DGs provides reproducible and clinically meaningful information for patient management.

CONTEXT.—: The process for identifying patients with monoclonal gammopathies is complex. Initial detection of a monoclonal immunoglobulin protein (M protein) in the serum or urine often requires compilation of analytical data from several areas of the laboratory. The detection of M proteins depends on adequacy of the sample provided, available clinical information, and the laboratory tests used. OBJECTIVE.—: To develop an evidence-based guideline for the initial laboratory detection of M proteins. DESIGN.—: To develop evidence-based recommendations, the College of American Pathologists convened a panel of experts in the diagnosis and treatment of monoclonal gammopathies and the laboratory procedures used for the initial detection of M proteins. The panel conducted a systematic literature review to address key questions. Using the Grading of Recommendations Assessment, Development, and Evaluation approach, recommendations were created based on the available evidence, strength of that evidence, and key judgements as defined in the Grading of Recommendations Assessment, Development, and Evaluation Evidence to Decision framework. RESULTS.—: Nine guideline statements were established to optimize sample selection and testing for the initial detection and quantitative measurement of M proteins used to diagnose monoclonal gammopathies. CONCLUSIONS.—: This guideline was constructed to harmonize and strengthen the initial detection of an M protein in patients displaying symptoms or laboratory features of a monoclonal gammopathy. It endorses more comprehensive initial testing when there is suspicion of amyloid light chain amyloidosis or neuropathies, such as POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) syndrome, associated with an M protein.

CONTEXT.—: Intraoperative consultation-frozen section diagnosis (FSD)-determines tumor pathology and guides the optimal surgical management of ovarian neoplasms intraoperatively. OBJECTIVE.—: To evaluate the diagnostic accuracy of the FSD and analyze the discrepancy between the FSD and final diagnosis. DESIGN.—: This is a retrospective study of 618 ovarian neoplasm FSDs from 2009 to 2018 at a tertiary health care center. The discrepant cases were reviewed and reevaluated by gynecologic and general surgical pathologists. The outcomes of interest were performing unnecessary procedure, returning for a second surgery, and 30-day postoperative mortality. RESULTS.—: The sensitivity and the positive predictive value of the FSD were lower in borderline tumors than in benign and malignant epithelial ovarian tumors. Major and minor discrepancies were identified in 5.3% (33 of 618) and 12.3% of (76 of 618) cases, respectively. A root cause analysis of the major discrepant cases showed that sampling error accounted for 43% (14 of 33). The discrepancy distributions of gynecologic and general surgical pathologists were statistically similar in the overall cohort (P = .65). The overall κ for diagnostic agreement among gynecologic pathologists, general surgical pathologists, and final diagnosis was 0.18 (0.10-0.26, P < .001), implying only a slight overall agreement. Of the major discrepant cases, only 3 had a clinical implication. One overdiagnosed patient underwent an unecessary procedure, and 2 underdiagnosed patients were recommended to return for a second surgery. No patient had 30-day postoperative mortality. CONCLUSIONS.—: Frozen section diagnosis remains a definitive diagnostic tool in ovarian neoplasms and plays a crucial role in guiding intraoperative surgical management.