Editors: Rouzan Karabakhtsian, MD, PhD, professor of pathology and director of the Women’s Health Pathology Fellowship, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, NY; S. Emily Bachert, MD, associate pathologist, Brigham and Women’s Hospital, Boston; Amarpreet Bhalla, MD, assistant professor of pathology, Albert Einstein College of Medicine, Montefiore Medical Center; Divya Sharma, MD, associate professor, Department of Pathology and Laboratory Medicine, University of Cincinnati Medical Center; and Paula Toro, MD, pathology resident, Cleveland Clinic.
E-cadherin mutational landscape and outcomes in breast invasive lobular carcinoma
March 2025—Invasive lobular carcinoma is characterized by loss of E-cadherin expression and CDH1 gene inactivation. The reliability and reproducibility of diagnosis for this tumor type is suboptimal and could be improved by better understanding the histomolecular and clinical heterogeneity of such tumors. The authors analyzed the relationship between the presence, type, or position of CDH1 mutations, E-cadherin expression, and clinicopathological features, including outcome, in a retrospective series of 251 primary invasive lobular carcinomas (ILC) with a median follow-up of 9.5 years. The mutational status of CDH1 (the gene encoding E-cadherin) was determined by RNA sequencing of frozen tumor samples. E-cadherin immunohistochemistry was performed with antibodies directed against the intracellular (clone 4A2C7) and extracellular (clone NCH38) domains. IHC expression of p120 and β-catenin was also assessed in E-cadherin diffusely positive cases. Three major patterns of E-cadherin membrane expression were identified by IHC, with good agreement between the two clones (overall concordance, 83.8 percent; Kappa, 0.67). They included null/focal expression (10 percent or less) (72.8 percent of cases for 4A2C7 and 83.8 percent for NCH38), heterogeneous expression (11–89 percent) (19.2 percent of cases for 4A2C7 and 6.9 percent for NCH38), and diffuse expression (90 percent or more) (eight percent of cases for 4A2C7 and 9.3 percent for NCH38). E-cadherin membranous expression, when present, was abnormal (incomplete labeling or reduced intensity, or both). ILC with diffuse E-cadherin expression showed abnormal β-catenin or p120-catenin staining in 21 percent of cases. Interestingly, these cases with diffusely expressed E-cadherin had a CDH1 mutation rate as high as the E-cadherin null/focal cases (approximately 70 percent) but were enriched in nontruncating mutations. The authors also demonstrated an association between CDH1 mutation location and E-cadherin protein expression. Intracytoplasmic domain mutations correlated with a divergent E-cadherin IHC phenotype (intracellular clone 4A2C7, 10 percent or less; extracellular clone NCH38, 10 percent or more). Clinicopathological correlation analyses found that stromal amount (inversely correlated with tumor cellularity) and tumor-infiltrating lymphocytes were less abundant in ILC for E-cadherin null/focal cases. In addition, CDH1 truncating mutations were associated with radiohistologic size discordance and identified in multivariate survival analyses as an independent poor prognostic factor in terms of metastasis risk and breast cancer-related mortality. This study highlighted the importance of determining the precise mutational status of CDH1 in the clinical, radiological, histologic, and phenotypic expression of lobular carcinoma. These findings should be taken into account in future attempts to improve the criteria or methods for diagnosing ILC, as well as for clinicobiological studies dedicated to this tumor type.
Djerroudi L, Bendali A, Fuhrmann L, et al. E-cadherin mutational landscape and outcomes in breast invasive lobular carcinoma. Mod Pathol. 2024;37(10). doi.org/10.1016/j.modpat.2024.100570
Correspondence: Dr. Anne Vincent-Salomon at anne.salomon@curie.fr
Role of immunohistochemistry in diagnosing pilomatrical tumors
Pilomatrical skin tumors harbor mutations in CTNNB1, which encodes for β-catenin, a downstream effector of the Wnt signaling pathway responsible for the differentiation, proliferation, and adhesion of epithelial stem cells. Downstream molecules, such as CDX2, LEF1, and SATB2, in the Wnt signaling pathway could be useful diagnostic markers for differentiating pilomatricoma from pilomatrical carcinoma. The authors conducted a study to investigate the potential of IHC to differentiate pilomatricoma from pilomatrical carcinoma and to differentiate them both from other cutaneous adnexal tumors. They studied 88 cases of cutaneous tumors (14 pilomatrical carcinomas, 18 pilomatricomas, 13 basal cell carcinomas, 12 squamous cell carcinomas, 12 sebaceous carcinomas, 10 Merkel cell carcinomas, seven trichoblastomas, and two hidradenocarcinomas) using a broad panel of IHC markers—β-catenin, SATB2, CDX2, LEF1, Ber-EP4, and PRAME. Pilomatricoma and pilomatrical carcinoma displayed greater than 75 percent nuclear staining for β-catenin. CDX2 also strongly stained pilomatrical tumors but was seen in only a small fraction of cells in pilomatricoma. SATB2 and Ber-EP4 expression were noted only in a subset of pilomatrical carcinoma and pilomatricoma, whereas LEF1 showed strong, diffuse nuclear positivity in both. Among the IHC markers evaluated, none could distinguish between pilomatricoma and pilomatrical carcinoma. However, the combined use of β-catenin and CDX2 markers may assist in not only confirming the pilomatrical nature of the proliferation but also in differentiating benign from malignant cases when there is significant presence of CDX2 staining. The authors concluded that despite these findings, diagnosis should continue to primarily rely on thorough histopathologic examination.
Alnaqshanbandi SM, McAfee JL, Ko JS, et al. Role of immunohistochemistry in the diagnosis of pilomatrical tumors. Am J Surg Pathol. 2024:48(12):1543–1550.
Correspondence: Dr. Shira Ronen at ronens@ccf.org
Focal cortical dysplasia in patients with Rasmussen’s encephalitis
Rasmussen’s encephalitis is a rare, predominantly pediatric epilepsy disorder of unknown etiology. It typically affects a single cerebral hemisphere and has such histological characteristics as cortical chronic inflammation, gliosis, and neuronal loss. The etiopathogenesis of Rasmussen’s encephalitis (RE) remains unknown, with genetic, infectious, and autoimmune factors speculated to play a role. Although the histologic findings in RE are well described, few studies have investigated a large cohort of cases looking for the coexistence of RE with focal cortical dysplasia (FCD). Therefore, the authors conducted a retrospective review of RE patients who underwent surgical resection of brain tissue between 1979 and 2021. Relevant patient history was retrieved and histologic slides reviewed. The histologic severity of RE was described using criteria established by Carols A. Pardo, MD (Pardo CA, et al. Epilepsia. 2004;45(5):516–526). The observed patterns of FCD (namely Ia, Ib, IIa, and IIb) were described using the International League Against Epilepsy (ILAE) classification. Thirty-eight resection specimens from 31 patients were analyzed for the study. Seventeen (54.8 percent) patients were male. Average age at surgery was eight years (range, 2–28 years). Twenty-seven (71.1 percent) resection specimens from 23 (74 percent) patients showed evidence of coexistent FCD. Most cases with FCD resembled the ILAE type Ib (n=23) pattern. Cases of RE that did not show FCD were Pardo stage one (n=5) or stage four (n=6), with all Pardo stage two and three cases demonstrating FCD. The authors concluded that FCD was found in most (74 percent) patients with RE. The most frequently observed pattern of FCD was ILAE Ib.
Galev G, Prayson RA. Focal cortical dysplasia is a frequent coexistent pathology in patients with Rasmussen’s encephalitis. Ann Diagn Pathol. 2024;68. doi.org/10.1016/j.anndiagpath.2023.152224
Correspondence: Dr. Richard A. Prayson at praysor@ccf.org
Development of a deep learning model for assessing pathological tumor response after neoadjuvant therapy
Neoadjuvant therapy followed by surgery has become the standard of care for locally advanced esophageal squamous cell carcinoma (ESCC). Accurately assessing pathological response, which is critical to determining therapeutic efficacy for the disease, can be laborious and inconsistent between observers. Therefore, the authors conducted a study as part of an effort to develop an interpretable deep learning model for efficiently assessing pathological response after neoadjuvant therapy for ESCC. Their retrospective study involved 451 samples from two branches of Fudan University Shanghai Cancer Center, Shanghai, China: 337 ESCC resection specimens obtained from 2020 to 2021 at the Pudong branch (group one) and 114 obtained from 2021 to 2022 at the Puxi branch (external group two) of the cancer center. Whole slide images (WSI) from these two groups were generated using different scanning machines to test the ability of the model to handle color variation. Two senior and two junior pathologists independently assessed pathological response. The senior pathologists annotated tumor beds and residual tumor percentages on WSI to determine consensus labels. A total of 1,850 image patches were also randomly extracted from group one WSI and underwent binary classification for tumor viability. A deep learning model employing knowledge distillation was developed to automatically classify positive patches for each WSI and estimate the viable residual tumor percentages. Spatial heat maps were output for model explanations and visualizations. The approach achieved high concordance with pathologist consensus, with an R2 of 0.8437, RAcc0.1 of 0.7586, and RAcc0.3 of 0.9885, which was comparable to that of the two senior pathologists (R2 of 0.9202/0.9619, RAcc0.1 of 0.8506/0.9425, RAcc0.3 of 1.000/1.000) and surpassed that of the two junior pathologists (R2 of 0.5592/0.5474, RAcc0.1 of 0.5287/0.5287, RAcc0.3 of 0.9080/0.9310). Visualizations enabled localization of residual viable tumor to augment microscopic assessment. The authors concluded that their study illustrates the potential for deep learning to aid in assessing pathological response. Spatial heat maps and patch examples provide intuitive explanations of model predictions, engendering clinical trust. Use of interpretable computational pathology could enhance the efficiency and consistency of tumor response assessment and aid in oncology treatment decisions.
Wang Y, Zhang W, Chen L, et al. Development of an interpretable deep learning model for pathological tumor response assessment after neoadjuvant therapy. Biol Proced Online. 2024. doi.org/10.1186/s12575-024-00234-5
Correspondence: Yuan Li at lumoxuan2009@163.com
Comparison of primary and metastatic fumarate hydratase-deficient renal cell carcinomas
Fumarate hydratase-deficient renal cell carcinomas are rare neoplasms characterized by wide morphologic heterogeneity and pathogenetic mutations in the fumarate hydratase (FH) gene. Because they often show aggressive behavior and rapidly diffuse to distant organs, novel therapeutic scenarios have been explored, including EGFR inhibitors and PD-L1 expression for targeted immunotherapy. The authors conducted a study in which they investigated 11 primary FH-deficient renal cell carcinomas and seven distant metastases to evaluate tumor heterogeneity, even in metastatic sites, and estimate the rates at which the tumors spread to various organs. The tumors were also tested for IHC PD-L1 expression and EGFR mutations. Most metastatic cases involved the abdominal lymph nodes (four of seven, 57 percent), followed by the peritoneum (three of seven, 42 percent), liver (two of seven, 29 percent), and lungs (one of seven, 14 percent). Six metastatic localizations were histologically documented, revealing a morphologic heterogeneous architecture that often differed from that of the corresponding primary renal tumor. Peritoneal involvement morphologically resembled a benign reactive mesothelial process or primary peritoneal mesothelioma, suggesting the need to perform an IHC panel that includes staining for PAX8 and FH to reach a diagnosis. A pure low-grade succinate dehydrogenase-looking primary FH-deficient renal cell carcinoma too was recorded. With respect to therapy, significant PD-L1 labeling was found in 60 percent of primary renal tumors, but none of them carried pathogenetic EGFR mutations. The data show that FH-deficient renal cell carcinoma also may be morphologically heterogeneous in metastases, which involve the lymph nodes, liver, and peritoneum more frequently than other renal tumors. Due to the high frequency of the latter (42 percent), pathologists should be concerned about ruling out mesothelial-derived mimickers and the occurrence of rarer, primary, low-grade-appearing types. Unlike EGFR mutations, PD-L1 expression could be a possible predictive biomarker for therapy to address these tumors.
Calio A, Marletta S, Stefanizzi L, et al. Comparison of primary and metastatic fumarate hydratase-deficient renal cell carcinomas documents morphologic divergence and potential diagnostic pitfall with peritoneal mesothelioma. Mod Pathol. 2024;37(9). doi.org/10.1016/j.modpat.2024.100561
Correspondence: Dr. Guido Martignoni at guido.martignoni@univr.it
Common expression of INSM1 in HPV-OPSCC in relation to neuroendocrine transformation or aggressive behavior
INSM1 has emerged as a robust marker for neuroendocrine differentiation, prompting its use as a standalone marker for neuroendocrine differentiation in various sites. INSM1 staining could be an especially practical tool for evaluating human papillomavirus-associated oropharyngeal squamous cell carcinoma (HPV-OPSCC) because high-grade neuroendocrine transformation may be exceedingly difficult to recognize on morphologic grounds alone, even though it portends highly aggressive clinical behavior. INSM1 has been touted as a standalone first-line marker of neuroendocrine differentiation in tumors of the head and neck, based on a sensitivity of 99 percent and specificity of 98 percent. The authors conducted a study to determine the incidence of INSM1 expression in HPV-OPSCC and assess its role in determining neuroendocrine transformation and clinical aggressiveness. Forty-six consecutive nonselected HPV-OPSCC were stained with INSM1 and synaptophysin. In addition, two clinically matched cohorts of aggressive (n=28) and nonaggressive (n=26) HPV-OPSCC were retrospectively stained with INSM1 and synaptophysin to determine the prognostic significance of INSM1 staining. In all, 42 percent of HPV-OPSCC showed positive INSM1 staining, but synaptophysin was not co-expressed in any cases. In select cases based on clinical behavior, INSM1 staining was observed more frequently in nonaggressive than aggressive tumors (50 and 21.4 percent, respectively; P=.03). The authors found that INSM1 expression is a common finding in HPV-OPSCC and typically is not linked with true neuroendocrine transformation or aggressive behavior. Indeed, INSM1 expression is more commonly observed in nonaggressive cancers. The authors concluded that relying on INSM1 staining alone to recognize neuroendocrine differentiation in HPV-OPSCC could be deleterious.
Bhardwaj S, Veremis B, Fernandino R, et al. The common expression of INSM1 in HPV-related oropharyngeal squamous cell carcinomas is not associated with true neuroendocrine transformation or aggressive behavior. Am J Surg Pathol. 2024;49(1):20–26.
Correspondence: Dr. William Westra at william.westra@mountsinai.org