Key Takeaways
- Biphasic mesothelioma is the second most common cell subtype, accounting for 20–30% of all mesothelioma cases. It contains both epithelioid and sarcomatoid cells — at least 10% of each must be present for the diagnosis.
- Prognosis depends heavily on the ratio of epithelioid to sarcomatoid cells. A higher proportion of epithelioid cells generally means a better prognosis, since epithelioid cells grow more slowly and respond better to treatment.
- Sarcomatoid cells make biphasic mesothelioma particularly challenging — they are irregular in size, lack defined edges, are difficult to completely remove with surgery, and are the most resistant to treatment of all cell types.
- Diagnosing biphasic mesothelioma requires a biopsy to examine the cellular makeup of the tumor. Accurate diagnosis demands specialized pathology expertise because of the difficulty in identifying and distinguishing the two cell types.
- Multimodal treatment — combining surgery with chemotherapy and/or radiation — has shown the highest success rate among biphasic patients, measured by post-treatment survival time.
- Treatment plans must be tailored to each patient’s specific situation, with the cellular composition of the tumor being a key factor in determining the approach.
What is Biphasic Mesothelioma?
Along with the origin sites of mesothelioma (like around the lungs or abdomen), mesothelioma is
also classified based on the types of cells that comprise it. Biphasic mesothelioma occurs when
two distinct cell types have a significant presence in the tumor; in this case, these are epithelioid
and sarcomatoid cells. There must be at least 10% of each type of cell present for a
mesothelioma case to be categorized as “biphasic.” Epithelioid cells are uniform in grouping,
have visible nuclei, and grow relatively slowly (when cancerous). Sarcomatoid cells do not have
a characteristic uniformity; they are irregular in size and tumor growth. Because they do not have
definitive edges like epithelioid cells do, sarcomatoid growths are much more difficult to
completely remove with surgery.
Biphasic mesothelioma is the second most common manifestation of mesothelioma, accounting
for about 20-30% of all mesothelioma cases. The most common form of mesothelioma is
epithelioid mesothelioma, which has the best prognosis and projected life expectancy. Given that
the biphasic manifestation also has epithelioid cells, the prognosis of the cancer is dependent
upon the ratio of epithelioid to sarcomatoid cells. Sarcomatoid mesothelioma is the rarest form of
mesothelioma and has the worst prognosis, as the cells are most resistant to treatment. So, if the
tumors are able to be visualized on a cellular level to determine the proportion of different cell
types, then doctors are better equipped to make treatment decisions. Sarcomatoid cells are
notoriously difficult to treat. Their growth patterns, lack of “predictability,” and typical late
detection make it markedly more difficult to both diagnose and treat biphasic mesothelioma.
Given the rarity of the biphasic manifestation, too–only researchers with a keen eye are able to
accurately diagnose biphasic mesothelioma. A biopsy is necessary for the cell type distinction of
mesothelioma (and its consequent treatment plan(s)).
Multimodal Treatment
The best course of action for biphasic mesothelioma is multimodal treatment, or a unique
combination of different techniques. Oftentimes, surgery and chemotherapy (or radiotherapy) is
used together most frequently and with the best results. Even though multimodal treatment has
its limitations, it had the highest success rate (quantified through survival time post-treatment)
among all biphasic mesothelioma treatment plans. It is important that treatment plans are created
with patient-specific needs and goals in mind, especially concerning the cellular makeup of
biphasic tumors.
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Frequently Asked Questions
What is biphasic mesothelioma?
Biphasic mesothelioma is a subtype of mesothelioma in which the tumor contains two distinct cell types — epithelioid and sarcomatoid. For a mesothelioma case to be classified as biphasic, at least 10% of each cell type must be present. It is the second most common cell subtype, accounting for approximately 20–30% of all mesothelioma diagnoses.
What are epithelioid and sarcomatoid cells?
These are the two types of cells that can make up mesothelioma tumors:
- Epithelioid cells — uniform in grouping, have large visible nuclei, and grow relatively slowly when cancerous. They form distinct clusters with defined edges, making them easier to identify and surgically remove. Epithelioid mesothelioma has the best prognosis of the three subtypes.
- Sarcomatoid cells — irregular in size and growth pattern, without the characteristic uniformity of epithelioid cells. They lack defined edges, making surgical removal much more difficult, and are the most resistant to treatment. Sarcomatoid mesothelioma has the worst prognosis.
In biphasic mesothelioma, both cell types are present in the same tumor, creating a mixed picture for diagnosis and treatment.
Why does the ratio of cell types matter in biphasic mesothelioma?
The ratio of epithelioid to sarcomatoid cells directly affects prognosis and treatment decisions. A tumor that is predominantly epithelioid (e.g., 80% epithelioid, 20% sarcomatoid) will generally behave more like epithelioid mesothelioma — growing more slowly and responding better to treatment. A tumor that is predominantly sarcomatoid will be more aggressive, harder to treat, and carry a worse prognosis. This is why visualizing the cellular makeup through biopsy is essential before determining a treatment plan.
How is biphasic mesothelioma diagnosed?
Diagnosing biphasic mesothelioma requires a tissue biopsy — a sample of the tumor must be examined at the cellular level to identify and quantify the proportion of epithelioid and sarcomatoid cells. This distinction cannot be made through imaging alone. Because of the complexity of identifying two different cell types within one tumor, accurate diagnosis often requires specialized pathology expertise. The rarity of the biphasic subtype means it can be misclassified if the pathologist doesn’t have experience with mesothelioma.
What is multimodal treatment and why is it used for biphasic mesothelioma?
Multimodal treatment means using two or more therapies in combination rather than relying on a single approach. For biphasic mesothelioma, the most common combination is surgery plus chemotherapy and/or radiation therapy. This approach has shown the highest success rate among biphasic patients because the two cell types respond differently to treatment — epithelioid cells may respond well to surgery, while sarcomatoid cells may require chemotherapy or radiation to address. Using multiple therapies targets both cell populations simultaneously.
Can biphasic mesothelioma be surgically removed?
Surgery may be an option depending on the tumor’s location, stage, and cellular composition — but it is more complicated than with purely epithelioid tumors. The sarcomatoid component of biphasic tumors lacks defined edges, making complete surgical removal significantly more difficult. Even after surgery, sarcomatoid cells are more likely to remain and continue growing. This is why surgery for biphasic mesothelioma is almost always combined with chemotherapy or radiation to target any remaining cancer cells.
How does biphasic mesothelioma compare to the other subtypes?
The three mesothelioma cell subtypes, ranked by prognosis:
- Epithelioid (50–70% of cases) — best prognosis, slowest growth, most responsive to treatment
- Biphasic (20–30% of cases) — mixed prognosis depending on the ratio of epithelioid to sarcomatoid cells
- Sarcomatoid (10–20% of cases) — worst prognosis, most aggressive, most treatment-resistant
A biphasic tumor with a predominantly epithelioid composition may behave similarly to an epithelioid case, while one dominated by sarcomatoid cells will be closer to a sarcomatoid prognosis.
What should I do if I’ve been diagnosed with biphasic mesothelioma?
If you or a loved one has been diagnosed with biphasic mesothelioma or another asbestos-related disease, understanding the cellular composition of your tumor is an important first step — it directly shapes your treatment plan and prognosis. Ask your oncologist about the ratio of epithelioid to sarcomatoid cells in your biopsy results. For information about your legal options, call (800) 505-6000 or fill out our contact form for a free consultation.
