Pathobiology

Pathology of the Fallopian Tube: Tubal Involvement by Ovarian Tumors and Incidental Findings in the Nontumoral Setting

The fallopian tube is thought to be the site of origin of most high-grade serous carcinomas (HGSCs). However, how often the tube is abnormal in the setting of other ovarian tumors is unknown. The aim of this study is to define the frequency of tubal abnormalities in the tumoral (<i>n</i> = 245) and nontumoral (<i>n</i> = 184) setting. We found that in ovarian tumors, 52.2% of the tubes were normal, while 39.2% were affected by the tumor. Abnormal tubes were found in 80% of HGSCs, in 21% of mucinous carcinomas, in 83.3% of seromucinous carcinomas, in 33.3% of endometrioid carcinomas, in 20% of clear-cell carcinomas, and in 10.5% of borderline tumors. Among normal tubes, almost 70% were histologically normal; transitional metaplasia was present in 17.4%, endometriosis in 8.1%, and adenofibroma in 2.2%, and 1.1% had an incidental serous intraepithelial tubal carcinoma. To conclude, the fallopian tube is abnormal in most serous carcinomas, and in a smaller number of endometrioid, clear-cell and mucinous carcinomas as well as borderline tumors. It is often abnormal in seromucinous tumors, but larger series are needed to study this rare subtype.

The Role of Cytokeratin 7 and Cytokeratin 19 Immunohistochemistry in the Evaluation of Human Papillomavirus-Induced Cervical Squamous Precursor Epithelial Lesions

Introduction: Cervical cancer is the fourth common cancer in women worldwide. In most cases, the disease is induced by persistent high-risk human papillomavirus (HPV) infection. This study aimed to assess the role of cytokeratin 7 (CK7) and cytokeratin 19 (CK19) in HPV-induced cervical epithelial lesions using tissue microarray (TMA). Methods: A retrospective cohort study included females with cervical low-grade intraepithelial lesion (LSIL), high-grade intraepithelial lesion (HSIL), and squamous cell carcinoma (SCC). TMA was constructed using specimens of 270 cases and 233 control tissues. CK7 and CK19 immunohistochemistry was scored as negative or positive. Follow-up information was gathered. Results: CK7 was negative in about 85% of LSILs and positive in 55% of HSILs (p < 0.001). CK19 showed positivity in about 50% of LSILs and 77% of the HSILs (p < 0.001). For cases with available follow-up data, about 69% of CK7-positive LSILs progressed to higher grade lesions and 64% of CK7-positive HSILs showed progression to higher grades (CIN2 to CIN3) or to SCC. Regarding CK19, nearly 66% positive LSILs progressed to HSIL whereas, 62% of positive HSILs showed progression. LSILs with positivity for both markers progressed to HSIL in 70% of cases. Conclusion: CK7 and CK19 positivity are significantly associated with higher grade HPV-induced cervical lesions. Lesions with combined CK7 and CK19 positivity have a higher risk of progression to higher grade lesions.

Origin of Residual Tumor Masses in BRCA1/2-Driven Ovarian Carcinomas Treated by Neoadjuvant Chemotherapy: Selection of Preexisting BRCA1/2-Proficient Tumor Cells but Not the Gain of Second ORF-Restoring Mutation

<b><i>Introduction:</i></b> Tubo-ovarian carcinomas (OCs) are highly sensitive to platinum-based neoadjuvant chemotherapy (NACT) but almost never demonstrate complete pathologic response. <b><i>Methods:</i></b> We analyzed paired primary and residual tumor tissues from 30 patients with hereditary <i>BRCA1/2</i>-driven OCs (<i>BRCA1</i>: 17; <i>BRCA2</i>: 13), who were treated by carboplatin/paclitaxel NACT (median number of cycles: 3, range: 3–6). <i>BRCA1/2</i> and <i>TP53</i> genes were analyzed by the next-generation sequencing. The ratio between <i>TP53</i> mutation-specific versus wild-type reads was considered to monitor the proportion of tumor and non-tumor cells in the tissue sample, and the ratio between <i>BRCA1/2-</i>mutated and wild-type reads was used to estimate the presence of cells with the loss or retention of heterozygosity (LOH or ROH, respectively). <b><i>Results:</i></b> All 30 OCs had <i>BRCA1/2</i> LOH in primary tumor and carried somatic <i>TP53</i> mutation. Twenty-eight OCs had sufficient tumor cell cellularity in the post-NACT tissue to evaluate the ratio between mutated and wild-type <i>BRCA1/2</i> alleles. Five (18%) out of 28 informative tumor pairs showed transition from LOH to ROH during NACT presumably affecting all or the vast majority of residual tumor cells. There were no signals of the emergence of a second open reading frame-restoring <i>BRCA1/2</i> mutation. <b><i>Conclusion:</i></b> Chemonaive <i>BRCA1/2</i>-driven carcinomas may contain a fraction of tumor cells with preserved <i>BRCA1/2</i> heterozygosity. NACT can cause a selection of pre-existing <i>BRCA1/2</i>-proficient tumor cells, without gaining secondary reversal <i>BRCA1/2</i> mutations.

Relative Telomere Length in Cervical Exfoliated Cells among Women with High-Risk Human Papillomavirus

<b><i>Introduction:</i></b> This study investigates and compares the relative telomere length (RTL) outcome of high-risk (hr) human papillomavirus (HPV)-infected normal, low-grade squamous intraepithelial lesion (LSIL), and high-grade squamous intraepithelial lesion (HSIL) cervical samples to HPV-free normal cervical samples. <b><i>Methods:</i></b> This study used archived cervical samples and obtained cytology and histology data. HPV genotyping was conducted using Sanger sequencing, and RTL was performed using real-time quantitative polymerase chain reaction. <b><i>Results:</i></b> This study investigated 287 cervical samples, including 100 normal and hr-HPV-negative samples from the control group, 44 normal and hr-HPV-infected samples, and 143 SIL and hr-HPV-infected samples. The RTL in hr-HPV-infected samples, including the SIL and normal sample groups, was significantly longer than that in the control group. RTL in HSIL (5.13 ± 3.22) and LSIL (2.86 ± 2.81) was significantly different (<i>p</i> < 0.001). The RTL of cervical intraepithelial neoplasia (CIN1) lesion (3.53 ± 2.53) differed significantly (<i>p</i> < 0.001) when compared to CIN2 and CIN3 lesions combined (12.04 ± 10.51). The risk of developing cervical cancer was associated with RTL and decreased with RTL. <b><i>Conclusion:</i></b> This study revealed the strong potential of the RTL test in identifying women at risk of developing cervical cancer.

Microbiome and Cervical Cancer

Persistent infection with some types of mucosal human papillomavirus (HPV) is the etiological factor for the development of cervical cancer and its precursor lesions. Besides, several cofactors are known to play a role in cervical disease onset and progression either by favoring or by preventing HPV infection and persistence. The microbiome of a healthy female genital tract is characterized by the presence of 1 or few varieties of lactobacilli. However, high-throughput studies addressing the bacterial diversity and abundance in the female genital tract have shown that several factors, including hormonal levels, hygiene habits, and sexually transmitted diseases may disrupt the natural balance, favoring the outgrowth of some groups of bacteria, which in turn may favor some pathological states. Recently, the vaginal microbiome has emerged as a new variable that could greatly influence the natural history of HPV infections and their clinical impact. In this context, changes in the vaginal microbiome have been detected in women infected with HPV and women with HPV-associated lesions and cancer. However, the role of specific bacteria groups in the development/progression or prevention/regression of HPV-associated pathologies is not well understood. In this review we summarize the current knowledge concerning changes in vaginal microbiome and cervical disease. We discuss the potential functional interplay between specific bacterial groups and HPV infection outcomes.

Roles of Cancer Histology Type and HPV Genotype in HPV ctDNA Detection at Baseline in Cervical Cancer: Implications for Tumor Burden Assessment

Introduction: Human papillomavirus circulating tumor DNA (HPV ctDNA) is a promising biomarker for monitoring cervical cancer. HPV ctDNA level at baseline (before treatment) reflects tumor burden. However, reported HPV ctDNA detection rates at baseline have shown variations across studies, suggesting the existence of other potential contributing factors. This study aimed to identify additional factors that might influence HPV ctDNA detection at baseline, focusing on histology type and HPV genotypes (high-risk genotypes HPV16 and HPV18). Methods: We retrospectively analyzed blood samples at baseline prior to treatment from 92 patients diagnosed with HPV16- or HPV18-associated cervical cancer (FIGO IA2–IIIC2) between 2013 and 2020. HPV ctDNA was evaluated using digital droplet PCR. Results: HPV ctDNA was detected at baseline in 41.3% of cases. Locally advanced cervical cancers had a higher (p = 0.028) detection rate at baseline than early stage cervical cancers. HPV ctDNA positivity was significantly (p = 0.048) higher for HPV18 (60%) than for HPV16 (34.3%). Adenocarcinoma/adenosquamous carcinoma had a higher HPV ctDNA detection rate at baseline (54.2%) than squamous cell carcinoma (36.8%) but not significantly (p = 0.212) higher. Conclusion: This study found the impact of histology and HPV genotype on HPV ctDNA at baseline in cervical cancer. HPV18 and adenocarcinoma were associated with a higher baseline HPV ctDNA detection rate. These results suggest the need for different HPV ctDNA approaches for analyzing tumor burden. This finding may also serve as a useful reference for posttreatment surveillance studies.

Lack of Association between IFNL3 Polymorphism and Human Papillomavirus Infection and Their Progression in HIV-Infected Women Receiving Antiretroviral Treatment

<b><i>Background:</i></b> It has been reported that interferon-λ3 (<i>IFNL3)</i>might influence the pathogenesis and clearance of human papillomavirus (HPV) infection. The impact of <i>IFNL3</i> single-nucleotide polymorphism (SNP) on HPV infection is currently unknown. The aim of this study was to investigate the association between variants in the <i>IFNL3</i> region and HPV infection in women with human immunodeficiency virus (HIV) infection. <b><i>Methods:</i></b> A total of 236 HIV patients, including 65 HPV-negative and 171 HPV DNA-positive women, were enrolled into this study. The <i>IFNL3</i> rs12979860 polymorphism was genotyped using a predesigned TaqMan SNP genotyping assay. <b><i>Results:</i></b> Data showed no significant differences in genotypes or allele frequencies between the HPV DNA-positive and the HPV-negative women (<i>p</i> > 0.05). After dividing the HPV-positive women according to cytology results into patients with abnormal and normal lesions, the genotype and allele distribution of the SNP did not significantly differ between the 2 groups (<i>p</i> > 0.05). <b><i>Conclusions:</i></b> Our results showed that the <i>IFNL3</i> rs12979860 polymorphism is not a major determinant of the susceptibility to HPV infection and their progression to abnormal cervical lesions in women living with HIV.

Lymphocyte Subsets in Cervicovaginal Lavage Specimens of HIV-Infected Women: A Surrogate Risk Marker of HPV-Associated Cervical Lesions

Introduction: To better understand the role of mucosa immunity in the development of cervical carcinoma in HIV infection, cervical lymphocyte subsets were characterized in HIV+ and HIV− women, as well as their relation to HPV-associated cervical lesions. Methods: Eighty-three (52 HIV+, 31 HIV−) cell suspensions of cervicovaginal lavage (CVL) and 52 HIV+ peripheral blood (PB) samples were assessed by flow cytometry to evaluate lymphoid populations. High-risk (HR) HPV was assessed in liquid-based cytology and HIV mRNA in PB in the same patients. Results: Cervical CD4+ T cells and CD4+/CD8+ ratio were decreased (p < 0.0001) and cervical CD8+ T cells were increased (p = 0.0080) in HIV+ women. These patients had lower CD4+ T-cell percentages in CVL compared to PB (p = 0.0257), and the opposite was true for CD8+ T cells (p = 0.0104). They also had a higher prevalence of high-grade squamous intraepithelial lesions (SILs) with an increased prevalence of HR HPV. Cervical CD8+ T cells were increased in HR HPV+ patients (p = 0.0300) and related to higher prevalence of SILs (p = 0.0001). Discussion/Conclusion: Cervical lymphoid populations can be characterized by flow cytometry, showing a distinct cervical T-cell compartment in HIV+ women. This may represent a surrogate risk marker of HPV-associated cervical lesions in this population and prompt further research on this subject, contributing to improving patients’ management.

Diagnostic Pitfalls Related to Morular Metaplasia in Endometrioid Carcinoma: An Underestimated Issue

Here, we present a case that highlights the crucial pitfalls related to the presence of morular metaplasia (MM) in endometrioid carcinoma, which are insufficiently recognized in the routine pathology practice. A 45-year-old woman underwent hysterectomy with rectosigmoidectomy due to a 11-cm mass involving uterus, right ovary, and rectosigmoid colon. Histologically, the lesion appeared as a predominantly solid carcinoma with a minor glandular component. Results of the first immunohistochemical analysis suggested a colorectal origin (PAX8-, CK7-, WT1-, hormone receptors-, and CDX2+ in the absence of mucinous features). Subsequent immunohistochemistry (nuclear β-catenin+, CD10+, and low ki67 in the solid areas) supported a diagnosis of endometrioid carcinoma with diffuse MM. This case remarks that morphological and immunohistochemical features of MM may conceal the glandular architecture and the typical immunophenotype of endometrioid carcinomas. Acknowledging the diagnostic issues related to MM appears crucial to avoid misdiagnosis and inappropriate patient management.

Trop2 Expression in Correlation to the Molecular Subtype in Vulvar Squamous Cell Carcinomas

Introduction: Targeted therapy with antibody-drug conjugates (ADCs) has achieved promising results in the treatment of different solid tumors. Sacituzumab-Govitecan (SG), a humanized anti-Trop2 monoclonal antibody linked with the cytotoxic topoisomerase I inhibitor SN-38, has been approved for the treatment of metastatic triple-negative breast cancer. The treatment approach with SG requires the expression of Trop2 within the tumor cells. Trop2 is overexpressed in many other cancer types, suggesting a broader therapeutic application beyond breast cancer to these ADCs. We explore expression of Trop2 vulvar squamous cell carcinomas (VSCCs) and how this relates to molecular classification. Methods: Immunohistochemical Trop2 expression was evaluated on diagnostic biopsies of VSCC using an immunoreactive score. Staining results were compared to the molecular subtype of VSCC. Results: Fifty-seven cases were included in the study. 63.2% of VSCC were p16−ve/p53abn (HPV-independent (p53abn)) molecular subtype, 29.8% p16+ve/p53wt (HPV-associated) and 1.4% p16−ve/p53wt (HPV-independent (p53wt)) tumors. All diagnostic biopsies (N = 57) showed at least a weak Trop2 expression. Moderate and strong expression was seen in 15/17 (88.2%) of the p16−ve/p53abn, 32/36 (88.8%) of the p16+ve/p53wt and 3/4 (75%) of the p16−ve/p53wt molecular subtype. Expression was significantly higher, as assessed by H score, in the HPV-associated VSCC, compared to HPV-independent. Conclusion: VSCCs have high expression of Trop2 and represents a promising therapeutic target. Clinical trials exploring Trop2-directed ADCs such as SG are warranted in this rare cancer type, including in the prognostically poor HPV-independent VSCC with a TP53-mutation (p16−ve/p53abn molecular subtype). The targetable molecule, Trop2, can be easily assessed by immunohistochemistry on diagnostic biopsies from VSCC.

Grainyhead-Like 2 Expression Is Associated with Disease Progression, Chemoresistance and Poor Survival in Tubo-Ovarian High-Grade Serous Carcinoma

<p>Introduction: Grainyhead-like 2 (GRHL2) regulates epithelial-to-mesenchymal transition (EMT) in cancer. This study analyzed the expression and prognostic role of GRHL2 in high-grade serous carcinoma (HGSC). Methods: GRHL2 protein expression by immunohistochemistry was analyzed in 411 HGSC (198 effusions, 213 surgical specimens). Expression score was generated by combination of staining extent and intensity and was assessed for association with clinicopathologic parameters and survival. Results: GRHL2 expression was significantly higher in effusions compared to surgical specimens in both analysis of all specimens (p < 0.001) and patient-matched tumors (n = 39 patients; p < 0.001). Expression was additionally higher in post-chemotherapy compared to chemo-naive effusions (p < 0.001). Higher GRHL2 score in effusions was associated with a trend for shorter overall survival (OS; p = 0.088). Higher GRHL2 score in surgical specimens was significantly related to nonoptimal (>0 cm) debulking (p = 0.004), non-complete chemoresponse at diagnosis (p = 0.003), primary chemoresistance (p = 0.045), and shorter OS (p = 0.038) and progression-free survival (PFS; p = 0.024). Both OS and PFS findings remained significant in Cox multivariate analysis (OS: p = 0.048; PFS: p = 0.04). Conclusion: GRHL2 is overexpressed in HGSC effusions compared to solid lesions, possibly reflecting altered EMT status. However, high expression in solid lesions is associated with chemoresistance and poor survival, possibly due to mediation of tumor cell migration and invasion. </p>

HPV ctDNA as a Biomarker for Monitoring Disease Progression in HPV16/18-Associated Cervical Cancer

Introduction: Cervical cancer, primarily driven by oncogenic HPV16/18, often relapses despite standard treatments. HPV circulating tumor DNA (ctDNA), which reflects tumor-derived genetic material in the bloodstream, has emerged as a promising noninvasive biomarker for monitoring disease progression. Methods: A prospective study was conducted on 20 patients with HPV16/18-associated cervical cancer. Posttreatment blood samples were collected, and HPV ctDNA levels were measured using droplet digital PCR. The correlation between HPV ctDNA levels and disease progression was examined. Results: HPV ctDNA was detected in 21% (18/85) of samples, with 6% (5/85) showing positivity. Patients without disease progression (n = 15) were HPV ctDNA negative, indicating a false positivity rate of zero. HPV ctDNA concentrations appeared higher in samples collected before or during disease progression, suggesting a potential association with disease status. Patients with positive HPV ctDNA tended to have shorter progression-free survival compared to those with negative ctDNA. Conclusions: This study suggests that HPV ctDNA may aid in monitoring disease progression in patients with HPV16/18-associated cervical cancer, highlighting the need for further validation.

LRP1B Expression as a Putative Predictor of Response to Pegylated Liposomal Doxorubicin Treatment in Ovarian Cancer

<b><i>Background:</i></b> Pegylated liposomal doxorubicin (PLD) is among the most active therapies for recurrent/progressive ovarian cancer (OC). Low-density lipoprotein receptor-related protein 1B (LRP1B) is one of the 10 most significantly deleted genes in human cancers. It mediates endocytosis of several factors from the cellular environment including liposomes. Although the LRP1B role in cancer has not been fully disclosed, its contribution to resistance to liposomal therapies has been hypothesized. This study aimed to evaluate the impact of LRP1B protein as a possible marker of response to PLD in patients with OC. <b><i>Methods:</i></b> LRP1B expression and response to PLD were analyzed in OC cell lines by qRT-PCR and PrestoBlue viability assay, respectively. LRP1B protein expression was evaluated for the first time, in tumor samples from PLD-treated patients and controls (other chemotherapies) by immunohistochemistry. Association of LRP1B staining score (determined based on intensity and percentage of positively stained cells) with clinicopathological features, response to therapy and survival outcomes was evaluated. <b><i>Results:</i></b> OC cells with increased expression of LRP1B were more sensitive to PLD. LRP1B staining score was associated with clinicopathological features, response to therapy, and survival outcomes. Higher LRP1B levels were associated with prolonged progression-free survival. This association was more evident in patients treated with PLD and in responders to PLD. <b><i>Conclusion:</i></b> Our results support a possible role of LRP1B as a predictor of response to PLD in patients with OC.

Histological Prognostic Factors of Endometrial Cancer in Patients with Adenomyosis: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> A better endometrial cancer (EC) prognosis in patients with coexistent adenomyosis has been hypothesized based on a different prevalence of favorable EC histological prognostic factors. However, pooled risk of EC unfavorable histological prognostic factors in patients with adenomyosis has never been calculated. <b><i>Objectives:</i></b> We aimed to assess the risk of EC unfavorable histological prognostic factors in patients with adenomyosis. <b><i>Methods:</i></b> All studies with data about histological prognostic factors of EC in patients with and without adenomyosis were included. Relative risk for each unfavorable histological prognostic factor of EC, such as nonendometrioid histotype, FIGO grade 3, FIGO stage II–IV, lymphovascular space invasion (LVSI), and deep myometrial invasion, was calculated in patients with adenomyosis compared to patients without adenomyosis. <b><i>Results:</i></b> Seven studies with 4,439 patients were included in the quantitative analysis. EC patients with adenomyosis showed a pooled RR of 0.77 (<i>p</i> = 0.05) for nonendometrioid histotype, 0.55 (<i>p</i> < 0.00001) for FIGO grade 3, 0.60 (<i>p</i> = 0.005) for FIGO stage II–IV, 0.75 (<i>p</i> = 0.004) for LVSI, and 0.65 (<i>p</i> = 0.001) for deep myometrial invasion. <b><i>Conclusion:</i></b> EC patients with adenomyosis have a significantly decreased risk for unfavorable histological prognostic factors of EC compared to EC patients without adenomyosis. Such findings might explain the supposed better EC prognosis in patients with adenomyosis.

Long Non-Coding RNA ARAP1-AS1 Facilitates the Progression of Cervical Cancer by Regulating miR-149-3p and POU2F2

<b><i>Background:</i></b> Emerging research has demonstrated that long non-coding RNAs (lncRNAs) attach great importance to the progression of cervical cancer (CC). LncRNA ARAP1-AS1 was involved in the development of several cancers; however, its role in CC is far from being elucidated. <b><i>Methods:</i></b> Real-time PCR (RT-PCR) was employed to detect ARAP1-AS1 and miR-149-3p expression in CC samples. CC cell lines (HeLa and C33A cells) were regarded as the cell models. The biological effect of ARAP1-AS1 on cancer cells was measured using CCK-8 assay, colony formation assay, flow cytometry, Transwell assay and wound healing assay in vitro, and subcutaneous xenotransplanted tumor model and tail vein injection model in vivo. Furthermore, interactions between ARAP1-AS1 and miR-149-3p, miR-149-3p and POU class 2 homeobox 2 (POU2F2) were determined by bioinformatics analysis, qRT-PCR, Western blot, luciferase reporter and RNA immunoprecipitation assay, respectively. <b><i>Results:</i></b> The expression of ARAP1-AS1 was enhanced in CC samples, while miR-149-3p was markedly suppressed. Additionally, ARAP1-AS1 overexpression enhanced the viability, migration, and invasion of CC cells. ARAP1-AS1 downregulated miR-149-3p via sponging it. ARAP1-AS1 and miR-149-3p exhibited a negative correlation in CC samples. On the other hand, ARAP1-AS1 enhanced the expression of POU2F2, which was validated as a target gene of miR-149-3p. <b><i>Conclusion:</i></b> ARAP1-AS1 was abnormally upregulated in CC tissues and indirectly modulated the POU2F2 expression via reducing miR-149-3p expression. Our study identified a novel axis, ARAP1-AS1/miR-149-3p/POU2F2, in CC tumorigenesis.

Deciphering Breast Origin in Malignant Effusions: The Diagnostic Utility of an MGP, GATA-3, and TRPS-1 Immunocytochemical Panel

Introduction: Defining the origin of metastatic cancer is crucial for establishing an optimal treatment strategy, especially when obtaining sufficient tissue from secondary malignancies is limited. While cytological examination is often used in this diagnostic setting, morphologic analysis alone often fails to differentiate metastases derived from the breast from other primaries. The hormone receptor, human epidermal growth factor receptor-2, gross cystic disease fluid protein 15, and mammaglobin immunohistochemistry are often used to diagnose metastatic breast cancer. However, their effectiveness decreases in estrogen receptor (ER)-negative breast cancers, including the triple-negative breast cancer (TNBC) subtype. Methods: We conducted a comprehensive evaluation of GATA-binding protein 3 (GATA-3), trichorhinophalangeal syndrome type 1 (TRPS-1), and Matrix Gla Protein (MGP) immunochemistry across 140 effusion cytology specimens with metastatic adenocarcinoma derived from various primaries, including the breast, colon, pancreaticobiliary, lung, tubo-ovarian, and stomach. Results: The expression rates of these immunomarkers were significantly higher in metastatic cancers originating from the breast than other primaries. In TNBC, TRPS-1 (80.00%) and MGP (65.00%) exhibited higher positivity rates compared to GATA-3 (40.00%). Additionally, our data suggest that an immunohistochemical panel comprising MGP, GATA-3, and TRPS-1 significantly enhances the detection of metastatic breast cancer in effusion cytology specimens, including TNBC in particular. When considering dual-marker positivity, the diagnostic accuracy was found to be 89.29% across all breast cancer subtypes and 92.93% for TNBC. Conclusions: MGP appears to be a robust marker for identifying metastatic breast cancer in malignant effusions, especially TNBC. MGP notably enhances diagnostic accuracy when incorporated together with GATA-3 and TRPS-1 in an immunohistochemical panel.