Mesothelioma is a rare and aggressive cancer that primarily originates in the thin lining of the lungs, abdomen, or heart. Cytology, the examination of cells, serves as a key diagnostic method for this disease. This approach offers a less invasive alternative compared to more involved diagnostic procedures.
Understanding Mesothelioma Cytology
Cytology involves the microscopic examination of individual cells or small cell clusters to detect abnormalities. For mesothelioma, it analyzes cells from body fluids or tissue scrapings, serving as an initial diagnostic step to identify malignant cells. Unlike histology, which studies larger tissue samples, cytology is a less invasive tool for early detection of cancerous cells.
Collecting Samples for Cytology
Fluid or cell samples for cytologic analysis in suspected mesothelioma cases are typically collected through minimally invasive procedures.
Thoracentesis: Involves inserting a needle into the pleural space to remove fluid from around the lungs, commonly used for pleural mesothelioma.
Paracentesis: Drains fluid from the abdominal cavity (peritoneal or ascitic fluid) for diagnosing peritoneal mesothelioma.
Pericardiocentesis: Collects fluid samples from the pericardium, the sac surrounding the heart, to diagnose pericardial mesothelioma.
Fine-needle aspiration (FNA): Extracts tissue from a tumor with a small needle, valuable when no fluid buildup is present.
These procedures are generally quick, often performed in an outpatient setting, and use local anesthesia to minimize discomfort.
Laboratory Analysis of Cytology Samples
Once collected, cytology samples undergo a process in the pathology laboratory. This involves preparing slides by concentrating cells, smearing, and using various staining techniques like Diff-Quik, Papanicolaou, and May-Grünwald-Giemsa to highlight cellular structures.
A cytopathologist examines these slides under a microscope for specific mesothelioma features, such as cell ball formation, nuclear pleomorphism, and giant atypical mesothelial cells. Distinguishing mesothelioma from reactive cells or other cancers like adenocarcinoma requires careful morphological assessment. Mesothelioma cells often appear in three-dimensional clusters with irregular outlines and may show intercellular windows.
Specialized Techniques
To confirm a diagnosis and differentiate mesothelioma from other malignancies, specialized techniques are employed. Immunocytochemistry (ICC) uses antibodies to bind to specific cellular proteins, helping identify cell origin. Specific markers, such as calretinin, help identify mesothelioma cells and differentiate them from other cancers like adenocarcinomas. Fluorescence in situ hybridization (FISH) is another advanced molecular technique used to detect genetic abnormalities, such as the homozygous deletion of the p16/CDKN2A gene, often observed in malignant mesothelioma.
Cytology’s Role in Mesothelioma Diagnosis
Cytology plays an important role in the initial diagnostic pathway for mesothelioma. Its lower invasiveness makes it a preferred first step for patients suspected of having the disease, especially when fluid has accumulated. Cytological examination findings, particularly when combined with immunocytochemistry, are instrumental in confirming the presence of malignant mesothelioma cells. This combined approach also helps differentiate mesothelioma from other similarly presenting cancers, such as lung adenocarcinoma.
While cytology can be indicative, its sensitivity for diagnosing mesothelioma from effusion samples ranges from 30% to 75%. Therefore, ambiguous cytological findings may necessitate a tissue biopsy for a definitive diagnosis, as biopsies provide more comprehensive architectural information. Despite this, cytology guides subsequent diagnostic decisions and influences treatment planning, contributing to a comprehensive understanding of the patient’s condition.