Biphasic mesothelioma tumors contain a combination of epithelioid and sarcomatoid cell types.
One of the two cell types often makes up the majority of the tumor.
Small amounts of biopsy tissue may not reveal both cell types and lead to misdiagnosis.
The cancer’s aggressiveness and response to treatment and prognosis differs according to which cell type is dominant.
Median survival generally ranges from 10 to 15 months after diagnosis.
Biphasic mesothelioma, also known as mixed mesothelioma, is one of the three major cell types. The biphasic tumor contains a mixture of epithelioid and sarcomatoid malignant cells, the other two major mesothelioma cell types. It is the second most common cell type of mesothelioma, comprising 20 to 40% of all mesothelioma cases.
Biphasic Mesothelioma Cell Characteristics
In biphasic mesothelioma, the epithelioid and sarcomatoid cells can either exist close together, or more often, in separate areas of the tumor.
The growth characteristics and behavior of biphasic mesothelioma vary according to the ratio of the two cell types.
- When there are more epithelioid cells than sarcomatoid cells, the tumor is more likely to spread locally.
- When there is a majority of sarcomatoid cells, local and distant metastases are more common.
Like all forms of mesothelioma, the extent and severity of symptoms associated with biphasic mesothelioma will vary with the degree of cancer advancement, and often include shortness of breath, chest pain or tightness, weight loss, and fever. Those patients whose tumors contain large proportions of sarcomatoid cells may also develop pain and breathing restrictions associated with tumor spread to the other side of the chest, as well as symptoms from metastases to local or more distant sites.
Diagnosis Requires The Presence of Both Cell Types
The diagnosis of biphasic mesothelioma is more common in pleural mesothelioma patients. A biphasic diagnosis requires both epithelioid and sarcomatoid cells in at least 10% of the tumor. When a radiological evaluation and/or laboratory test identifies mesothelioma in the chest, tumor tissue is then evaluated. A sample of the tumor is usually obtained with a biopsy. A biopsy is usually performed prior to surgery since the decision to perform radical surgery is influenced by cell type and, in the case of biphasic mesothelioma, the relative proportions of epithelioid and sarcomatoid malignant cells.
The selected method must also take into consideration the accuracy of the biopsy-based diagnosis. This is particularly important for patients with biphasic mesothelioma since preoperative biopsies usually provide rather small amounts of tumor tissue for testing and the epithelioid and sarcomatoid elements often grow in different parts of the tumor. As a result, the sample obtained may not be representative of the overall tumor makeup, leading to misdiagnosis. For example:
- Around 20 to 50% of patients with biphasic mesothelioma are initially classified as epithelioid.
- It is reported that as many as 44% of patients with an initial diagnoses of either biphasic or sarcomatoid had a final diagnosis of epithelioid cell type.
Such inaccuracies can have serious consequences, especially if a patient with epithelioid mesothelioma fails to undergo radical surgery because the tumor was initially classified as biphasic or sarcomatoid. In a recent report, a preoperative needle biopsy classified the cell type correctly only 44% of the time. Thoracotomy was the most accurate, correctly classifying cell type in 83% of cases, followed by thoracoscopy at 74%.
To prevent misdiagnosis, doctors use an advanced test known as immunohistochemistry, which can detect certain proteins in cells.
Treatment Success and Response Varies
Patients with biphasic mesothelioma usually have a poorer prognosis and may not be considered for as aggressive a treatment plan as other cell types. However, a number of other factors determine treatment options, and patients may be treated with any or all of the usual mainstays of trimodal therapy:
However, the effectiveness of trimodal treatment for biphasic mesothelioma varies considerably. Responses to therapy and outcomes are strongly affected by the relative amounts of epithelioid and sarcomatoid cells in a given case. Those with biphasic tumors where the epithelioid component predominates would be expected to have a more favorable response to treatment compared to those with sarcomatoid predominance.
Aggressive treatment of patients with mixed mesothelioma may reduce or eliminate epithelioid cells, but the sarcomatoid component is largely unaffected. As such, palliative care may be the best course for those patients with a large proportion of sarcomatoid cells. Palliative therapy may include radiation therapy to reduce tumor size, along with other measures to improve breathing and provide comfort and pain control. Limited surgical procedures such as pleurodesis or drainage of pleural effusions may also be considered if likely to provide greater patient comfort or relieve labored or painful breathing.
Prognosis Depends on Ratio of Cell Types
Studies show biphasic median survival is better than the sarcomatoid cell type, but worse compared to epithelioid tumors. In a study comparing the three, median survival was 11-15 months for biphasic mesothelioma. In the study, patients with more epithelial cells survived longer, but only by 16 days. Sarcomatoid cells are less responsive to treatment than epithelial cells. The more epithelial cells in a biphasic diagnosis, the better the prognosis may be, but only marginally, depending on the particular case.