Sarcomatoid Mesothelioma
What Is Sarcomatoid Mesothelioma?
Malignant mesothelioma is categorized into different histological subtypes based on the appearance and behavior of the cancer cells under a microscope. These subtypes help doctors understand how the disease is likely to progress and which treatments may work best. Learn more about histology and its relation to cancer.
Sarcomatoid mesothelioma is the least common but most aggressive of these subtypes. It is characterized by spindle-shaped cells that are arranged in a disorganized, fibrous pattern. These cells resemble mesenchymal cells, which are found in connective tissues, and they lack the organized structure seen in other mesothelioma subtypes, such as epithelioid.
Where Is Sarcomatoid Mesothelioma Found?
Sarcomatoid mesothelioma can develop in any of the serosal linings of the body, but it is most frequently found in the pleura, the thin membrane surrounding the lungs. It can also occur in the peritoneum (the lining of the abdominal cavity), and less commonly in the pericardium (the lining around the heart) or the tunica vaginalis (the lining of the testes). The pleural location is the most common site, as asbestos fibers often become lodged in the pleura after inhalation, leading to inflammation and tumor development.
How Does Sarcomatoid Mesothelioma Behave Compared to Other Cell Types?
Sarcomatoid mesothelioma is the most aggressive and least treatable of the three main mesothelioma cell types (epithelioid, sarcomatoid, and biphasic). It tends to grow and spread rapidly, often invading nearby tissues and organs. This subtype is highly resistant to treatment, including surgery, chemotherapy, and radiation. The disorganized structure of sarcomatoid cells makes them difficult to target with therapies, and they are less likely to respond to conventional treatments.
Patients with sarcomatoid mesothelioma typically have a poorer prognosis compared to those with epithelioid or biphasic mesothelioma. Studies suggest that the median survival for patients with this subtype is significantly shorter, often ranging from 6 to 12 months, depending on the stage of the disease and the treatment approach.
What Percentage of Cases Does Sarcomatoid Mesothelioma Represent?
Sarcomatoid mesothelioma is the least prevalent subtype, accounting for approximately 10% to 15% of all mesothelioma cases. Its rarity, combined with its aggressive nature, makes it one of the most challenging forms of mesothelioma to study and treat. The remaining cases are divided between the epithelioid subtype (55% to 65%) and the biphasic subtype (20% to 35%), which contains a mix of both epithelioid and sarcomatoid cells.
Additional Pertinent Information
The diagnosis of sarcomatoid mesothelioma is particularly challenging, as its cells can resemble those of other sarcomas or spindle-cell tumors. Pathologists rely on advanced diagnostic techniques, such as immunohistochemical staining and electron microscopy, to differentiate sarcomatoid mesothelioma from other malignancies. Accurate diagnosis is critical, as it allows patients to explore treatment options that may improve quality of life, even if curative treatments are not available.
In summary, sarcomatoid mesothelioma is the least common but most aggressive subtype of mesothelioma, primarily affecting the pleura but also found in other serosal linings. Its rapid progression and resistance to treatment present significant challenges, underscoring the importance of early and accurate diagnosis for patients facing this form of asbestos-related cancer.
How Sarcomatoid Mesothelioma Differs from Other Types
Sarcomatoid mesothelioma is distinct from the other two main mesothelioma subtypes—epithelioid and biphasic—in several critical ways, including its cellular structure, growth behavior, treatment resistance, and overall prognosis. These differences are essential for accurate diagnosis, treatment planning, and understanding patient outcomes.
Structure of Cells Under a Microscope
Under a microscope, sarcomatoid mesothelioma cells are spindle-shaped, elongated, and arranged in a disorganized, fibrous pattern. These cells resemble mesenchymal cells found in connective tissue, making them difficult to distinguish from other sarcomas or spindle-cell tumors. This lack of organization and differentiation complicates diagnosis and often requires advanced techniques like immunohistochemical staining or electron microscopy.
In contrast:
Epithelioid mesothelioma cells are cube-shaped or columnar and form organized structures such as tubules, papillae, or solid sheets. These cells closely resemble normal epithelial cells, making epithelioid mesothelioma easier to identify and distinguish from other cancers, such as adenocarcinoma.
Biphasic mesothelioma contains a mix of both sarcomatoid and epithelioid cells, with the proportion of each type varying from case to case. This mixed structure can complicate diagnosis, as the behavior of the tumor depends on the dominant cell type.
Growth Rate and Pattern
Sarcomatoid mesothelioma is the most aggressive of the three subtypes. It grows and spreads rapidly, often invading nearby tissues and distant organs. This subtype typically follows a highly invasive growth pattern, making it more challenging to contain and treat effectively.
In contrast:
Epithelioid mesothelioma is the least aggressive subtype. It tends to grow and spread more slowly, often following a localized growth pattern and spreading to nearby lymph nodes before advancing to other areas.
Biphasic mesothelioma exhibits a combination of growth behaviors, depending on the proportion of sarcomatoid and epithelioid cells. Tumors with a higher percentage of sarcomatoid cells tend to grow and spread more aggressively.
Treatment Resistance
Sarcomatoid mesothelioma is highly resistant to treatment. Its disorganized cellular structure and rapid progression make it less likely to respond to conventional therapies, including surgery, chemotherapy, and radiation. Patients with this subtype are often not candidates for aggressive surgical interventions, and treatment is typically focused on palliative care to improve quality of life.
In contrast:
Epithelioid mesothelioma is the most responsive to treatment among the three subtypes. Its organized cellular structure and slower growth rate make it more amenable to therapies such as surgery, chemotherapy, and radiation. Patients with epithelioid mesothelioma are often better candidates for aggressive surgical procedures and multimodal treatment approaches.
Biphasic mesothelioma has variable treatment responsiveness, depending on the ratio of sarcomatoid to epithelioid cells. Tumors with a higher proportion of epithelioid cells tend to respond better to treatment.
Prognosis Comparison
Sarcomatoid mesothelioma is associated with the poorest prognosis among the three subtypes. Studies show that patients with this subtype have a median survival of only 6 to 12 months, depending on factors such as disease stage, patient age, and overall health. Its aggressive nature and resistance to treatment contribute to this outcome.
In contrast:
Epithelioid mesothelioma has the best prognosis, with a median survival of 12 to 24 months. Its slower growth rate and better treatment responsiveness contribute to this more favorable outcome.
Biphasic mesothelioma has an intermediate prognosis, with survival rates depending on the proportion of sarcomatoid versus epithelioid cells. Patients with a higher percentage of epithelioid cells tend to have better outcomes.
Additional Pertinent Information
The differences between these subtypes underscore the importance of accurate diagnosis. Pathologists rely on advanced diagnostic techniques, such as immunohistochemical staining, molecular testing, and electron microscopy, to differentiate sarcomatoid mesothelioma from other subtypes and similar-looking cancers. This distinction is critical for determining the most appropriate treatment plan and providing patients with a realistic understanding of their prognosis.
In summary, sarcomatoid mesothelioma differs from other types in its disorganized cellular structure, rapid growth rate, high treatment resistance, and poor prognosis. These characteristics make it the most aggressive and challenging form of mesothelioma to treat, highlighting the need for early and accurate diagnosis to optimize patient care.
How Doctors Identify the Sarcomatoid Subtype
Accurately identifying the sarcomatoid subtype of mesothelioma is critical for determining the best treatment options and providing an accurate prognosis. Diagnosis involves a combination of biopsy, histological examination, and immunohistochemical testing. Expert pathology is essential, as sarcomatoid mesothelioma is often difficult to distinguish from other spindle-cell tumors, and misclassification can lead to inappropriate treatment and poorer outcomes.
Biopsy and Histology (Microscopic Review)
The first step in identifying the sarcomatoid subtype is obtaining a tissue sample through a biopsy. There are several methods for collecting biopsy samples, including:
Thoracoscopic biopsy: A minimally invasive procedure where a camera and instruments are inserted into the chest to collect tissue.
CT-guided needle biopsy: A needle is guided by imaging to collect tissue from the affected area.
Open surgical biopsy: A more invasive procedure used when other methods fail to provide sufficient tissue.
Once the tissue is collected, it is examined under a microscope by a pathologist. Sarcomatoid mesothelioma cells are spindle-shaped, elongated, and arranged in a disorganized, fibrous pattern. These cells resemble mesenchymal cells found in connective tissue, making them difficult to distinguish from other sarcomas or spindle-cell tumors. This lack of organization and differentiation often necessitates further testing to confirm the diagnosis.
Immunohistochemical Markers
To confirm the diagnosis and differentiate sarcomatoid mesothelioma from other cancers, pathologists use immunohistochemical (IHC) staining. This technique involves applying antibodies to the tissue sample to detect specific proteins expressed by mesothelioma cells. Key markers for sarcomatoid mesothelioma include:
Cytokeratin (CK): Sarcomatoid mesothelioma cells typically express cytokeratin, which helps distinguish them from other spindle-cell tumors, such as sarcomas, that are cytokeratin-negative.
Calretinin: While less commonly positive in sarcomatoid mesothelioma compared to the epithelioid subtype, it can still aid in diagnosis.
WT-1 (Wilms Tumor-1): A nuclear marker that is often expressed in mesothelioma, including sarcomatoid cases, but not in most other cancers.
D2-40 (podoplanin): Frequently positive in mesothelioma and useful in distinguishing it from other spindle-cell tumors.
Thrombomodulin: Another marker that can be expressed in sarcomatoid mesothelioma and is used as part of a diagnostic panel.
In contrast, markers such as S-100, desmin, and CD34 are typically negative in sarcomatoid mesothelioma but positive in other spindle-cell tumors, such as sarcomas or fibrous tumors. This helps pathologists rule out other cancers that may mimic sarcomatoid mesothelioma.
The use of a panel of markers, rather than relying on a single test, is critical for accurate diagnosis. Pathologists often use a combination of positive and negative markers to confirm the sarcomatoid subtype and exclude other possibilities.
Why Expert Pathology Matters
Diagnosing sarcomatoid mesothelioma is particularly challenging and requires specialized expertise. Misclassification is a significant concern, as sarcomatoid mesothelioma can resemble other spindle-cell tumors, such as sarcomas, or even benign conditions like reactive fibrosis. Studies have shown that general pathologists may misdiagnose mesothelioma in a significant number of cases, leading to inappropriate treatment.
Expert pathologists with experience in mesothelioma use advanced techniques, such as IHC staining and molecular testing, to ensure an accurate diagnosis. They are also more likely to recognize subtle differences in cell structure and staining patterns that distinguish sarcomatoid mesothelioma from other diseases. In some cases, a second opinion from a mesothelioma specialist is necessary to confirm the diagnosis.
Additional Considerations
Full-thickness biopsy samples: Providing pathologists with full-thickness tissue samples is crucial, as superficial samples may only show reactive changes rather than malignant cells.
Histological subtyping: Identifying the sarcomatoid subtype is important because it has the poorest prognosis and is the most resistant to treatment compared to epithelioid or biphasic mesothelioma.
Necropsy findings: In rare cases, the diagnosis may only be confirmed post-mortem, as some tumors are difficult to classify during a patient’s lifetime.
The identification of the sarcomatoid subtype of mesothelioma relies on a combination of biopsy, histological examination, and immunohistochemical testing. Key markers such as cytokeratin and WT-1 play a vital role in confirming the diagnosis. Expert pathology is essential to avoid misclassification, which can lead to inappropriate treatment and worse outcomes. By ensuring an accurate diagnosis, doctors can provide patients with the most effective treatment options and a clearer understanding of their prognosis.
How The Sarcomatoid Subtype Affects Treatment Decisions
The sarcomatoid subtype of mesothelioma is associated with the poorest prognosis among the three main histological subtypes (epithelioid, biphasic, and sarcomatoid). This subtype is more aggressive, less responsive to treatment, and often presents challenges in achieving effective disease control. Multimodal treatment approaches, which are more effective for the epithelioid subtype, tend to have limited success in sarcomatoid cases. Surgery, chemotherapy, and radiation therapy are often less effective due to the invasive and resistant nature of sarcomatoid tumors.
Chemotherapy remains the primary treatment option for sarcomatoid mesothelioma, with pemetrexed and cisplatin being the standard first-line agents. However, response rates are generally lower compared to the epithelioid subtype. Immunotherapy, particularly with immune checkpoint inhibitors like nivolumab and ipilimumab, has shown some promise in clinical trials, but the overall effectiveness is still under investigation. Radical surgery, such as extrapleural pneumonectomy or pleurectomy/decortication, is rarely recommended for sarcomatoid mesothelioma due to the poor outcomes and high risk of complications.
Eligibility for Surgery or HIPEC
Patients with sarcomatoid mesothelioma are typically not ideal candidates for aggressive surgical interventions. The diffuse and invasive nature of this subtype often makes complete resection of the tumor impossible. Additionally, the rapid progression of sarcomatoid mesothelioma limits the potential benefits of cytoreductive surgery combined with Hyperthermic Intraperitoneal Chemotherapy (HIPEC) for peritoneal cases. Surgery is generally reserved for palliative purposes, such as relieving symptoms like pleural effusion or improving quality of life.
Use of Immunotherapy for Aggressive Types
Immunotherapy is emerging as a potential option for sarcomatoid mesothelioma, particularly for patients who are not candidates for surgery or have failed standard chemotherapy. Immune checkpoint inhibitors, such as nivolumab and ipilimumab, have shown some efficacy in improving survival and controlling disease progression in sarcomatoid cases. However, the response rates are still lower compared to the epithelioid subtype, and further research is needed to optimize immunotherapy protocols for this aggressive form of mesothelioma.
Notes About Subtype-Specific Clinical Trials
Clinical trials focusing on sarcomatoid mesothelioma are limited but crucial for advancing treatment options. Key findings from these trials include:
The sarcomatoid subtype is less responsive to standard chemotherapy regimens, highlighting the need for novel therapeutic approaches.
Immunotherapy trials have shown some promise, but the results are not as robust as those seen in the epithelioid subtype.
Research into targeted therapies and gene therapy is ongoing, with the goal of identifying treatments that can overcome the resistance and aggressiveness of sarcomatoid tumors.
In summary, the sarcomatoid subtype of mesothelioma presents significant challenges in treatment, with limited effectiveness of standard therapies and a need for innovative approaches. Clinical trials remain essential for improving outcomes in this patient population.
Prognosis for Sarcomatoid Mesothelioma
Median Survival Time
The sarcomatoid subtype of mesothelioma is associated with the shortest median survival time among the three main subtypes. Studies indicate that the median survival for patients with sarcomatoid mesothelioma ranges from 4 to 12 months, depending on factors such as stage at diagnosis, treatment approach, and overall health. This is significantly shorter than the median survival for epithelioid mesothelioma, which can range from 12 to 30 months.
How Prognosis Changes with Stage/Anatomical Location
The stage of the disease and its anatomical location significantly impact the prognosis for sarcomatoid mesothelioma:
Early-Stage Disease (Stage I or II): Even in early stages, the prognosis for sarcomatoid mesothelioma is poor. Median survival rarely exceeds 12 months, even with aggressive treatment.
Advanced-Stage Disease (Stage III or IV): For late-stage sarcomatoid mesothelioma, median survival typically falls to 4–8 months due to the rapid spread of the disease and resistance to treatment.
Anatomical Location: Pleural mesothelioma (affecting the lining of the lungs) is the most common form of sarcomatoid mesothelioma and has a slightly better prognosis compared to peritoneal mesothelioma (affecting the abdominal lining). However, both forms are associated with poor outcomes.
Factors That Influence Outcomes
Several factors influence the prognosis for patients with sarcomatoid mesothelioma:
Treatment Center: Outcomes are often better at specialized mesothelioma treatment centers with access to clinical trials and advanced therapies.
Overall Health and Performance Status: Patients with good overall health and a high performance status may tolerate treatments better, but the aggressive nature of sarcomatoid mesothelioma limits the impact of these factors.
Age: Younger patients may have slightly better outcomes, but the prognosis remains poor overall.
Treatment Approach: Multimodal therapy has limited success in sarcomatoid cases, and most treatments are palliative rather than curative.
Histological Confirmation: Accurate diagnosis of the sarcomatoid subtype is crucial for setting realistic expectations and tailoring treatment plans.
In summary, the prognosis for sarcomatoid mesothelioma is poor, with median survival times ranging from 4 to 12 months. The aggressive nature of this subtype, combined with its resistance to standard treatments, underscores the need for continued research and innovation in treatment strategies.
Desmoplastic Mesothelioma: A Very Rare Sarcomatoid Variant
Desmoplastic mesothelioma is a rare and aggressive subtype of malignant mesothelioma, classified under the sarcomatoid variant. This form of mesothelioma is characterized by its dense fibrous tissue composition, which can make it challenging to distinguish from benign conditions such as fibrous pleurisy or pleural plaques. Its unique histological and clinical features warrant careful attention, particularly for individuals with a history of asbestos exposure.
Key Characteristics
Desmoplastic mesothelioma is defined by the dominance of fibrous tissue within the tumor, often comprising at least 50% of the tumor bulk. Histologically, it exhibits a storiform (whorled) pattern of collagen deposition, areas of collagen necrosis, and bland acellular collagen. Despite its fibrous appearance, focal cytological features of malignancy, such as hyperchromatic nuclei, are present, aiding in its differentiation from benign fibrotic conditions.
Diagnostic Challenges
The diagnosis of desmoplastic mesothelioma is notoriously difficult, especially when relying on small biopsy samples. Its fibrous nature can mimic non-specific reactive pleural fibrosis or other benign conditions. Immunohistochemical staining, particularly for cytokeratin, is a critical tool in distinguishing desmoplastic mesothelioma from other spindle cell neoplasms, such as sarcomas or spindle cell squamous carcinomas. Additionally, the presence of distant metastases, particularly to the bone, can provide further evidence of its malignant nature.
Clinical Implications
Desmoplastic mesothelioma is associated with a poor prognosis. The mean survival time from symptom onset to death is typically less than one year, with sarcomatoid and biphasic variants generally exhibiting more aggressive behavior compared to epithelial mesotheliomas. Metastases are common, often involving the liver, lungs, adrenal glands, kidneys, and, in some cases, bones. This aggressive clinical course underscores the importance of early and accurate diagnosis.
Asbestos Exposure and Risk
As with other forms of mesothelioma, desmoplastic mesothelioma is strongly linked to asbestos exposure. Studies indicate that up to 90% of mesothelioma cases occur in individuals with a history of occupational asbestos exposure. The latency period between exposure and disease onset can range from decades, making it a significant concern for individuals exposed to asbestos in the past.
Conclusion
Desmoplastic mesothelioma represents a challenging and aggressive form of sarcomatoid mesothelioma. Its diagnosis requires a combination of histological, immunohistochemical, and clinical findings, with a high index of suspicion in patients with a history of asbestos exposure. Given its poor prognosis, ongoing research into early detection and treatment strategies is critical to improving outcomes for affected individuals.
Legal and Compensation Considerations for Sarcomatoid Mesothelioma
Sarcomatoid mesothelioma is the rarest and most aggressive histological subtype of mesothelioma—but a diagnosis still qualifies for legal compensation through lawsuits, asbestos trust fund claims, and government benefits. Like all forms of mesothelioma, sarcomatoid is caused almost exclusively by asbestos exposure.
Why the Sarcomatoid Subtype Matters in Legal Claims:
Faster progression often makes early legal action more urgent
Limited treatment options may lead to higher unreimbursed medical costs
Poorer prognosis can increase the need for expedited settlements or survivor claims
Because sarcomatoid mesothelioma is less responsive to treatment, patients and families often face additional challenges—both medically and financially. We act quickly to help clients file before critical deadlines expire and to preserve claims on behalf of the family in cases where time is limited.
Our firm has helped thousands of mesothelioma clients—including many with the sarcomatoid subtype—recover compensation for:
Medical expenses (including non-covered or experimental treatments)
Lost income or retirement benefits
Home care and support services
Pain, suffering, and emotional distress
Wrongful death claims for surviving spouses or children
👉 Learn more about mesothelioma lawsuits and legal options
📞 Or call 833-4-ASBESTOS for a free consultation.
Frequently Asked Questions About Sarcomatoid Mesothelioma
Q: Is sarcomatoid mesothelioma harder to treat?
A: Yes. It is generally the most aggressive and least responsive to standard treatments like surgery and chemotherapy. That’s why early detection and legal action are so important.
Q: Does having the sarcomatoid subtype affect my eligibility for compensation?
A: No. Compensation depends on your exposure history, diagnosis, and applicable legal deadlines—not the cell type. Patients with sarcomatoid mesothelioma are equally entitled to file lawsuits or trust claims.
Q: Can family members file a claim if the patient has passed away?
A: Yes. Surviving spouses, children, or estate representatives can file wrongful death claims or continue claims already started. Our firm can help ensure these are handled quickly and respectfully.