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Rare Mesothelioma Cell Types

The only way to confirm a mesothelioma diagnosis is through pinpointing cell type. There are three main mesothelioma cell types, including epithelioid, sarcomatoid, and biphasic mesothelioma. By determining the type of cell, physicians can better understand prognosis and determine a proper treatment plan for the cancer patient. There are also rare subtypes of mesothelioma cells that can challenge the diagnosis process and impact the treatment options available for the mesothelioma patient.

Mesothelioma cell types differ mostly in appearance and how they grow (metastasize). Rare cell types of mesothelioma include:

  • Adenomatoid mesothelioma
  • Benign mesothelioma
  • Cystic mesothelioma
  • Deciduoid mesothelioma
  • Small cell mesothelioma
  • Desmoplastic mesothelioma
  • Heterologous mesothelioma (osteosarcomatous and chondrosarcomatous)
  • Lymphohistiocytic mesothelioma
  • Papillary mesothelioma

As variants of the three main cell types listed above, these subtypes maintain many similar characteristics that help guide physicians in determining an effective treatment plan.

Epithelioid Mesothelioma Variations

Epithelial cells make up around 50 – 70% of mesothelioma cases. These cells are well-defined and form intricate branching patterns. Epithelial mesothelioma cells are slow-growing, allowing for more treatment options and a generally longer life expectancy.

Adenomatoid Mesothelioma

Adenomatoid mesothelioma, also referred to as glandular mesothelioma or microglandular mesothelioma, can be classified as benign or malignant. Adenomatoid cells line small, gland-like structures, and are usually found in the genital glands of both men and women.

  • Location: Small, gland-like structures, usually genital glands
  • Cell appearance: Flat or cube-shaped
  • Metastasis: Lace-like growth patterns

Cystic Mesothelioma

Cystic mesothelioma occurs in the form of cysts and has a better prognosis than most cases of mesothelioma. Most cases of cystic mesothelioma are benign, though some develop into malignant cancer or recur as malignant. More than half of reported patients have experienced recurrence. This type of cancer is most common in women of reproductive age.

  • Location: Pelvic peritoneum or abdominal cavity linings (most common), other pelvic structures like the omentum, uterus, bladder, and rectum (less common)
  • Cell appearance: Flat or cube-shaped cells, making smooth, thin-walled cysts connected by delicate fibrovascular tissues
  • Metastasis: Localized with no spreading

Deciduoid Mesothelioma

Most frequently seen in the abdomens of female patients, deciduoid mesothelioma is extremely rare, very unique, and has only been diagnosed in a few cases. Whereas the average survival rate of malignant pleural mesothelioma is around 1 year, deciduoid mesothelioma has a very poor prognosis of only about 5 or 6 months. The cause of this cancer is unknown, though some doctors feel that it’s caused by a hormonal imbalance and others suspect a correlation with asbestos exposure.

  • Location: Abdomen, linings of the lung (pleural)
  • Cell appearance: Large, polygonal or oval-shaped cells that form tumors made up of firm, white or gray nodules
  • Metastasis: Typically spreads and progresses, even with treatment

Papillary Mesothelioma

Papillary mesothelioma, also known as well-differentiated papillary mesothelioma (WDPM), is most common in women of reproductive ages, though men have also been diagnosed. Prognosis is typically favorable, as most cases are benign.

  • Location: Abdominal linings (peritoneum), tunica vaginalis, lung linings (pleura), areas of the male reproductive system
  • Cell appearance: Resemblance to normal, healthy cells
  • Metastasis: Slow, microscopic growth pattern that creates small projects that resemble fingers (papillae)

Sarcomatoid Mesothelioma Variations

Sarcomatoid mesothelioma is much harder to diagnose, and is more rare than epithelial. Sarcomatoid cells strongly resemble healthy tissue, making it difficult to identify as malignant. These types of cancer cells are aggressive and grow very fast, limiting treatment options and challenging life expectancy.

Desmoplastic Mesothelioma

Desmoplastic mesothelioma typically falls under the sarcomatoid cell type, though there have been epithelial and biphasic classifications in rare cases. With desmoplastic tumors, more than 50% of the tumor is composed of dense, fibrous tissue. As a sarcomatoid cancer, those with desmoplastic mesothelioma likely face a life expectancy of less than a year.

  • Location: Abdominal linings (peritoneum), tunica vaginalis, lung linings (pleura), areas of the male reproductive system
  • Cell appearance: Patternless
  • Metastasis: Can spread to the lung or chest wall, though spreading tissues look vastly similar to benign fibrous tissue

Lymphohistiocytoid Mesothelioma

Lymphohistiocytoid mesothelioma is composed of primarily sarcomatoid cells, though cases have seen a mix of epithelioid cells within the mesothelioma tumors as well, making it a subtype of biphasic mesothelioma. This cancer is commonly misdiagnosed as non-Hodgkin lymphoma, lymphoepithelial carcinoma and sarcomatoid carcinoma of the lung, and ganglioneuroma due to its makeup. These tumors are composed of dense bundles of inflammatory immune cells.

  • Location: Abdomen, linings of the lung (pleural)
  • Cell appearance: Large, polygonal, spindle-shaped histiocytoid cells, mixed with lymphocytes (white blood cells)
  • Metastasis: Tumors can spread to other regions of the body, potential for recurrence after surgical removal

Other Cell Type Variations

Some mesothelioma cancer subtypes don’t fall under sarcomatoid or epithelial, but maintain similar characteristics.

Benign Mesothelioma

Benign mesothelioma can occur as several different types. Less common than malignant mesothelioma, this benign disease is non-cancerous. Whereas malignant mesothelioma cancer symptoms typically take 20-50 years to manifest, benign forms can emerge at any time.

  • Location: Varies
  • Cell appearance: Varies
  • Metastasis: None

Heterologous Mesothelioma

Heterologous mesothelioma is one of the least understood subtypes due to its rarity. Heterologous tumors are different from others in that they contain bodily tissues from areas outside of the origin point, including bone, cartilage, and soft tissues. Common heterologous elements include osteosarcomatous and chondrosarcomatous.

  • Location: Pleural cavities, peritoneal cavities, or pericardial cavities
  • Cell appearance: Varies
  • Metastasis: Varies/unknown (There haven’t been enough cases to study. Most cases have been seen with aggressive sarcomatoid cells, though instances of biphasic and epithelial have also occurred.)

Osteosarcomatous Differentiation

In some cases of malignant pleural mesothelioma, osteosarcomatous differentiation has been recorded. Exceedingly rare, there is not much data for this type of mesothelioma, however, it’s classified by the presence of bone cells within the tumors.

Chondrosarcomatous Differentiation

Also exceedingly rare are malignant mesothelioma cases with chondrosarcomatous differentiation. The main classifying factor for these cases of mesothelioma is the presence of spindle-shaped cells from cartilage.

Small Cell Mesothelioma

Another commonly misdiagnosed cancer is small cell mesothelioma. Only seen in a few cases, doctors typically rely on their knowledge of common types of mesothelioma to determine their treatment approach. Tumors in this small cell cancer consist largely of small cells that grow in a pattern very similar to that of small cell carcinoma.

  • Location: Pleural cavities, peritoneal cavities, or pericardial cavities
  • Cell appearance: Varies
  • Metastasis: Growth patterns very similar to those of small cell carcinoma, but without stream, ribbon, or rosette appearances

Diagnosing Rare Forms of Mesothelioma

Diagnoses for rare types of mesothelioma parallels that of common types of the cancer. Examination of symptoms, imaging scans, and biopsies will all occur in an attempt to pinpoint the disease. Ultimately, a biopsy is the only way to definitively diagnose mesothelioma. In some cases, multiple biopsies may be necessary to figure out the exact type, since some tumors are composed of different types of tissues.

Mesothelioma Histology

Accurate diagnosis is key to determine prognosis and treatment options for a cancer patient. As with all cancers, more research is needed in the efforts to find a cure. Histology, the study of cellular anatomy, has been a large component in understanding different mesothelioma cell types and determining the best paths for treatment.

Histology first entails a biopsy, where tissue is removed to analyze. Tissue samples are preserved and embedded, making them easy to cut and segment. After sectioning, tissues are mounted and stained for a detailed view into cell structure. In addition to traditional histology methods, immunohistology is frequently used in mesothelioma diagnoses, utilizing antibodies to detect and identify proteins.

Treating Rare Forms of Mesothelioma

There usually isn’t a clear treatment plan for rare types of mesothelioma, leaving doctors to fall back on standard options. If a cell type is a variant of sarcomatoid or epithelial, this can limit or expand treatment potential. Sarcomatoid cells are harder to treat, and oftentimes surgery won’t be a viable option.

Common Treatment Options for Rare Mesothelioma Types
Adenomatoid
  • Benign: surgery
  • Malignant mesothelioma: multimodal treatment
Benign
Surgery to remove the tumor
Chondrosarcomatous
Surgery, chemotherapy and radiation
Cystic
Surgery is highly effective
Deciduoid
Desmoplastic
Heterologous
  • Chemotherapy
  • Radiation
  • Pleurodesis or paracentesis
Lymphohistiocytic
Multimodal treatment
Osteosarcomatous
Multimodal treatment
Papillary
  • Surgery as preferred option, as there is no metastasis
  • Radiation or chemotherapy can be used
Small cell

In addition to standard treatment options, clinical trials and alternative treatments are constantly being explored to improve patient comfort and survival rate.

Understanding Mesothelioma

Although rare, it’s important to understand the different types of mesothelioma. There are a variety of symptoms to look out for, and early diagnosis is key to addressing such an aggressive cancer.

If you or a loved one suspect mesothelioma, consult a physician right away. If you are already facing a diagnosis, look into your legal options to understand not just the disease, but all of the help available to you.

Sources

Allen, T. Recognition of histopathologic patterns of diffuse malignant mesothelioma in differential diagnosis of pleural biopsies. Archives of Pathology & Laboratory Medicine. November 2005;129(11)1415-1420.

American Cancer Society. About malignant mesothelioma. American Cancer Society . February 17, 2016.

Cagle P, Churg A. Differential diagnosis of benign and malignant mesothelial proliferations on pleural biopsies. Archives of Pathology & Laboratory Medicine. November 2005;129(11):1421-7. doi: 10.1043/1543-2165

Gupta A, Harish KR, Raghav P, et al. A Rare case of benign multicystic peritoneal mesothelioma: A clinical dilemma. Indian Journal of Surgery. June 2013;75(1)27-29. doi: 10.1007/s12262-011-0314-6

Hoekstra AV, Riben MW, Frumovitz M, et al. Well-differentiated papillary mesothelioma of the peritoneum: A pathological analysis and review of the literature. Gynecologic Oncology. July 2005;98(1)161-167. doi: 10.1016/j.ygyno.2005.03.031

Husain AN, Colby TV, Ordóñez NG, et al. Guidelines for pathologic diagnosis of malignant mesothelioma: A consensus statement from the International Mesothelioma Interest Group. Archives of Pathology & Laboratory Medicine. August 2009;133(8):1317-1331.

Klebe S, Mahar A, Henderson D, et al. Malignant mesothelioma with heterologous elements: clinicopathological correlation of 27 cases and literature review. Modern Pathology. June 26, 2008;21:1084-1094. doi: 10.1038/modpathol.2008.125

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