Mesothelioma Cell Types

Epithelioid Mesothelioma

Epithelioid mesothelioma is the most common cell type, accounting for approximately 70% of all mesothelioma diagnoses. It is also the cell type with the most favorable prognosis, with a median survival of 12 to 27 months — and significantly longer for patients who are eligible for aggressive multimodal treatment including surgery.

Under the microscope, epithelioid mesothelioma cells appear uniform and cuboidal (roughly cube-shaped) with clearly defined cell borders and visible nuclei. These cells tend to grow in organized, recognizable patterns rather than the chaotic, infiltrative patterns seen in other cell types. This structural regularity is one reason epithelioid tumors respond better to treatment — their organized growth makes them more amenable to surgical removal, and their cellular characteristics make them more susceptible to chemotherapy drugs.

Epithelioid Subtypes

Epithelioid mesothelioma is further divided into several histological subtypes based on the specific pattern of cell growth. While all epithelioid subtypes carry a better prognosis than sarcomatoid or biphasic mesothelioma, there are meaningful differences between subtypes:

• Tubulopapillary — Cells form tube-like and finger-like projections (papillae). This is one of the most common epithelioid subtypes and carries the most favorable prognosis among all mesothelioma subtypes. Well-differentiated tumors of this type have shown median survivals approaching 24-27 months with multimodal treatment.
• Acinar (Glandular) — Cells form small, gland-like clusters. This subtype resembles adenocarcinoma under the microscope and is one of the reasons IHC testing is essential — it must be distinguished from metastatic adenocarcinoma, which requires entirely different treatment.
• Solid — Cells grow in dense, sheet-like formations without distinct tubular or papillary architecture. While still epithelioid, the solid subtype tends to have a slightly less favorable prognosis than tubulopapillary, though it remains significantly better than sarcomatoid disease.
• Trabecular — Cells form cord-like strands or ribbons. This less common subtype has characteristics that fall between tubulopapillary and solid variants in terms of growth behavior and prognosis.

Biphasic (Mixed) Mesothelioma

Biphasic mesothelioma, also called mixed mesothelioma, accounts for approximately 20-25% of all mesothelioma diagnoses. As the name suggests, biphasic tumors contain both epithelioid and sarcomatoid cells within the same tumor mass. The median survival for biphasic mesothelioma is 10 to 15 months, though this varies significantly depending on the ratio of the two cell types present.

The defining characteristic of biphasic mesothelioma is that both epithelioid and sarcomatoid cell populations must be present in sufficient quantity to be identified. In practice, this means a tumor that is predominantly epithelioid with a small sarcomatoid component will behave — and respond to treatment — differently than a tumor with roughly equal proportions of both cell types or one that is predominantly sarcomatoid.

The Importance of Cell Type Ratio

Research consistently demonstrates that the ratio of epithelioid to sarcomatoid cells in a biphasic tumor is the single most important factor in determining prognosis for these patients:

• Predominantly epithelioid biphasic (>75% epithelioid cells) — Prognosis approaches that of pure epithelioid mesothelioma. These patients are generally better candidates for surgery and respond more favorably to chemotherapy. Median survival may reach 14-16 months or longer with multimodal treatment.
• Balanced biphasic (roughly 50/50 split) — Intermediate prognosis with median survival typically in the 10-12 month range. Treatment decisions require careful balancing of surgical aggressiveness with the understanding that the sarcomatoid component may limit long-term benefit.
• Predominantly sarcomatoid biphasic (>50% sarcomatoid cells) — Prognosis approaches that of pure sarcomatoid mesothelioma. These patients may benefit less from aggressive surgery and may be better served by systemic therapies including chemotherapy and immunotherapy.

How Cell Type Affects Treatment Decisions

Mesothelioma cell type is one of the primary factors oncologists consider when designing a treatment plan. Each cell type responds differently to surgery, chemotherapy, radiation therapy, and emerging immunotherapy treatments. The following outlines the general treatment approach for each cell type:

Epithelioid: Best Surgical Candidate

Patients with epithelioid mesothelioma who are otherwise healthy and have early-stage disease are the strongest candidates for aggressive multimodal treatment, which typically includes:

• Surgery — Pleurectomy/decortication (P/D) or extrapleural pneumonectomy (EPP) to remove as much visible tumor as possible. Epithelioid tumors' organized growth pattern gives surgeons the best chance of achieving complete macroscopic resection.
• Chemotherapy — First-line pemetrexed plus cisplatin (or carboplatin) achieves the highest response rates in epithelioid tumors, with some studies reporting objective response rates of 40% or higher.
• Immunotherapy — The FDA-approved nivolumab plus ipilimumab (Opdivo + Yervoy) combination has shown particular promise for epithelioid patients, and ongoing clinical trials continue to expand immunotherapy options.
• Radiation — Adjuvant radiation therapy may be used after surgery to target residual microscopic disease, particularly following P/D.

Sarcomatoid: Chemotherapy & Immunotherapy Focus

Because sarcomatoid mesothelioma's infiltrative growth pattern makes complete surgical removal extremely difficult, treatment for this cell type typically focuses on systemic therapies:

• Chemotherapy — Standard pemetrexed-platinum regimens may be offered, though response rates are lower than for epithelioid disease (typically 15-25% objective response rate).
• Immunotherapy — Emerging research suggests that sarcomatoid mesothelioma may actually respond better to immune checkpoint inhibitors than epithelioid mesothelioma in some cases, potentially because sarcomatoid tumors tend to have higher PD-L1 expression and greater tumor mutational burden.
• Palliative care — Given the aggressive nature of sarcomatoid disease, palliative interventions to manage symptoms and maintain quality of life are an essential component of the treatment plan.
• Clinical trials — Patients with sarcomatoid mesothelioma should strongly consider clinical trials that test new therapeutic approaches specifically designed for treatment-resistant tumors.

Biphasic: Treatment Tailored to Dominant Cell Type

Treatment planning for biphasic mesothelioma requires careful assessment of the epithelioid-to-sarcomatoid ratio:

• Predominantly epithelioid biphasic — May be treated similarly to pure epithelioid disease, including consideration for surgery with curative intent plus systemic therapy.
• Balanced or sarcomatoid-predominant biphasic — Treatment approach shifts toward systemic therapy (chemotherapy and immunotherapy) with a more cautious approach to major surgery, as the sarcomatoid component may limit the benefit of aggressive resection.
• Accurate ratio assessment — Adequate tissue sampling is critical for biphasic patients so that treatment can be appropriately matched to the tumor's actual composition.

Legal Rights & Compensation for Mesothelioma Patients

Regardless of your mesothelioma cell type, if your diagnosis is the result of asbestos exposure, you have legal rights. Mesothelioma is caused almost exclusively by asbestos exposure, and the companies that manufactured, distributed, and used asbestos-containing products knew of the health risks for decades before taking action to protect workers and consumers.

Mesothelioma patients and their families may be eligible for multiple sources of compensation:

• Asbestos trust fund claims — Over $30 billion remains available across 60+ active asbestos bankruptcy trust funds. Claims can typically be filed without going to trial and may result in payments within months.
• Personal injury lawsuits — Legal action against the companies responsible for your asbestos exposure. Settlements and verdicts in mesothelioma cases routinely reach six and seven figures.
• Wrongful death claims — Surviving family members can pursue compensation if a loved one has passed away from mesothelioma.
• VA disability benefits — Military veterans diagnosed with mesothelioma are typically rated at 100% disability by the VA, qualifying them for maximum monthly compensation and additional benefits.
• Workers' compensation — Available for those who were exposed to asbestos in the workplace, though benefits vary by state.

Time is a critical factor in mesothelioma legal claims. Statutes of limitations set deadlines for filing, and these deadlines vary by state. For patients with sarcomatoid mesothelioma or aggressive biphasic disease, where prognosis is shorter, expedited legal proceedings may be necessary to protect your rights. An experienced mesothelioma attorney can evaluate your situation and act quickly on your behalf at no upfront cost.