Thymic Carcinoma: A Review

Weakly supervised learning in thymoma histopathology classification: an interpretable approach

Introduction

Thymoma classification is challenging due to its diverse morphology. Accurate classification is crucial for diagnosis, but current methods often struggle with complex tumor subtypes. This study presents an AI-assisted diagnostic model that combines weakly supervised learning with a divide-and-conquer multi-instance learning (MIL) approach to improve classification accuracy and interpretability.

Methods

We applied the model to 222 thymoma slides, simplifying the five-class classification into binary and ternary steps. The model features an attention-based mechanism that generates heatmaps, enabling visual interpretation of decisions. These heatmaps align with clinically validated morphological differences between thymoma subtypes. Additionally, we embedded domain-specific pathological knowledge into the interpretability framework.

Results

The model achieved a classification AUC of 0.9172. The generated heatmaps accurately reflected the morphological distinctions among thymoma subtypes, as confirmed by pathologists. The model's transparency allows pathologists to visually verify AI decisions, enhancing diagnostic reliability.

Discussion

This model offers a significant advancement in thymoma classification, combining high accuracy with interpretability. By integrating weakly supervised learning, MIL, and attention mechanisms, it provides an interpretable AI framework that is applicable in clinical settings. The model reduces the diagnostic burden on pathologists and has the potential to improve patient outcomes by making AI tools more transparent and clinically relevant.

Thymic carcinosarcoma with melanocytic differentiation in a dog

Carcinosarcomas are very rare tumors in dogs. Although carcinosarcomas with melanocytic differentiation arising from organs other than the thymus have been described in humans, this type of tumor has not been reported in dogs in any part of the body. We observed such a tumor in the cranial mediastinum of an 11-year-old spayed female dachshund. The dog was admitted to the clinic because of coughing, sporadic regurgitation, and dyspnea. Thoracic ultrasonography and computed tomography revealed a large mediastinal mass that was surgically removed via sternotomy. The tumor was of thymic origin and demonstrated 3 distinct components: an epithelial component positive for pancytokeratin (AE1/AE3) and high molecular weight cytokeratin (CK5/CK6) with some cystic spaces; a mesenchymal component positive for vimentin; and in association with the epithelial part, a minor melanocytic component positive for Melan A. Histologic metastasis of the epithelial and melanocytic components was present within a tracheobronchial lymph node. The dog died 105 d after surgery, after an episode of acute dyspnea. Key clinical message: To the authors' knowledge, this is the first report of thymic carcinosarcoma with melanocytic differentiation.

Immunotherapy in thymic epithelial tumors: tissue predictive biomarkers for immune checkpoint inhibitors

Thymic epithelial tumors (TETs) are rare malignant neoplasms arising in the thymus gland. Nevertheless, TETs, including thymomas (TMs), thymic carcinomas (TCs), and thymic neuroendocrine neoplasms (TNENs), are the most common mediastinal malignancies overall. A multidisciplinary approach is required for the appropriate diagnostic and therapeutic management of TETs. To date, the main therapeutic strategies are largely depended on the stage of the tumor and they include surgery with or without neoadjuvant or adjuvant therapy, represented by platinum-based chemotherapy, radiotherapy or chemoradiotherapy. Immune checkpoint inhibitors (ICIs) are ongoing under evaluation in the advanced or metastatic diseases despite the challenges related to the very low tumor mutation burden (TMB) and the high incidence of immune-related adverse events in TETs. In this regard, predictive impact of tissue biomarkers expression such as programmed cell death ligand-1 (PD-L1), and other emerging biomarkers, as well as their optimal and shared interpretation are currently under evaluation in order to predict response rates to ICIs in TETs.

Thymic Adenocarcinoma With Metastasis to the Left Orbit: A Case Report

We present the case of a 57-year-old female who initially presented with a chief complaint of left-sided orbital headaches and associated left eyelid swelling. Initial imaging work-up with CT head/orbit revealed soft tissue enhancement of the left orbital roof, concerning for neoplastic process (primary lymphoma versus extracranial primary tumor versus metastatic tumor). Further imaging studies with CT chest/abdomen/pelvis revealed an anterior mediastinal mass, concerning for possible thymoma versus lymphoma. The patient underwent further consultation with the Hematology/Oncology and Ophthalmology Departments, which recommended definitive biopsies from both sites, which showed matching histologic findings of moderately differentiated enteric-type adenocarcinoma with positive staining for CDX2, an intestinal marker. Thymic carcinomas are rare cancers that account for approximately 0.06% of all malignancies and require a high degree of clinical suspicion. Extrathoracic metastases from thymic carcinomas, especially to the orbit, is a rare occurrence and the exact incidence of this phenomenon is unknown. This case represents the diagnostic challenges associated with a rare cancer type and underscores the importance of a multidisciplinary approach to patient care.

Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

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.