Deciduoid Mesothelioma

One defining characteristic of mesothelioma is the vast number of unique variations documented in medical literature. While doctors mainly classify the four primary types of mesothelioma based on their location in the body, a mesothelioma tumor can also be described by its histology, or the appearance and growth patterns of its composite cells. These mesothelioma cell types can be divided even further into specific subtypes, such as deciduoid mesothelioma.

Deciduoid mesothelioma is an unusual form of epithelial mesothelioma, the most common of all mesothelioma cell types. The term deciduoid reflects this subtype’s histological resemblance to a cellular transformation that takes place during the early stages of pregnancy. After conception, a hormone causes the lining of the uterus to take on new and distinct cellular characteristics. The new lining, which helps form the placenta, then becomes known as the decidua. Although the features of deciduoid mesothelioma and various other diseases appear remarkably similar to the decidua on a cellular level, they result from entirely different biological processes.

An Atypical Subtype

A rarely documented cancer, deciduoid mesothelioma is substantially different from the more common variations of the disease. While most mesothelioma cancers strike older men, early studies only found the deciduoid subtype in the abdomens of young women. And although nearly all mesotheliomas are caused by overabundant exposures to asbestos, many experts initially believed there was no link between deciduoid mesothelioma and asbestos whatsoever.

First described in 1985, deciduoid mesothelioma has been diagnosed in about 44 cases. As more cases emerged, doctors learned the disease was in fact not exclusive to the peritoneums of young women. Several cases involved men and older women. Deciduoid elements were also observed in pleural and pericardial mesotheliomas, and some patients disclosed a history of asbestos exposure.

Slightly less than half of all deciduoid mesotheliomas are pleural, meaning they form in the lining of the lungs. A roughly equal number of deciduoid cases occur in the peritoneum, which lines the abdomen. This distribution is atypical considering that about 75 percent of all mesotheliomas develop in the pleura.

Risk Factors and Causes

Medical experts do not know the exact cause of this cancer, but some consider asbestos or hormonal changes to be potential factors. Unlike most types of mesothelioma, deciduoid mesothelioma has not been conclusively linked to asbestos exposure. Some doctors speculate that asbestos is a contributing cause, yet only one-third of all known deciduoid patients disclosed a history of exposure.

Doctors who doubt the connection to asbestos speculate that a hormonal imbalance may help trigger the onset of deciduoid mesothelioma. Two patients were diagnosed during pregnancy. In one of these cases, a woman’s tumor was discovered during a Cesarean section. These findings seemed to support the hormonal hypothesis. However, researchers opted to rule out this possibility, citing negative test results for certain hormones that should have been present in patients.

Data initially suggested that more than half of all cases occurred in women. However, according to a 2018 study published in Archives of Pathology & Laboratory Medicine, recent reviews show just slightly more than half of all cases occur in men.

Diagnosis and Related Challenges

This cancer is difficult to diagnose not only because of its rarity, but also because it resembles other diseases. A deciduoid tumor is made up of firm, whitish gray nodules. Just as in the decidua, individual tumor cells are tightly packed and appear large and polygonal or oval-shaped. The extent of deciduoid features in mesothelioma tumors can vary significantly, ranging from small, isolated areas to the entire bulk of the tumor. The most common symptom patients experience is abdominal or chest pain, depending on the tumor’s location.

In the abdomens of young women, this type of mesothelioma resembles another type of tumor called pseudotumoral deciduosis. The two tumors have the same physical features and symptoms. Additionally, both illnesses show a history of being diagnosed in pregnant women and during Cesarean section. These similarities led some patients to be misdiagnosed with pseudotumoral deciduosis, a dangerous mistake considering that pseudotumoral deciduosis is generally non-cancerous. Cancer patients mistakenly diagnosed with this type generally do not receive the immediate care they need.

Prognosis and Treatment Options

For all forms of deciduoid mesothelioma, curative treatment options remain elusive. In patients treated with radical surgery followed by aggressive chemotherapy, the disease typically continues to progress despite the elimination of all signs of cancer. The typical treatment plan is therefore palliative, meaning it aims to control symptoms and prolong survival rather than cure the cancer.

While the most effective course of treatment for mesothelioma is an ongoing topic of debate, most experts agree that multimodal therapies represent the gold standard of care. These therapies include various combinations of standard cancer treatments like surgery, chemotherapy and radiation therapy. One example boasting noteworthy success rates is extrapleural pneumonectomy surgery combined with pre- or post-operative chemotherapy. However, some experts claim that the risks of this aggressive surgical technique commonly outweigh its potential benefits.

The only treatment found to increase survival in randomized trials was systemic chemotherapy, which can kill cancer cells that have spread to the lymph nodes and distant organs. One 2001 case study reported on a deciduoid peritoneal mesothelioma patient who received cytoreductive surgery and systemic chemotherapy. While the cancer did not return to his peritoneum after treatment, he showed no response to the chemotherapy and died of distant metastases five months after his initial diagnosis.

A short survival time is common among people diagnosed with deciduoid mesothelioma. The median survival rate is five or six months after diagnosis, as compared to eight to 12 months for nondeciduoid peritoneal mesothelioma. Just as with other types of mesothelioma, some patients may live with the cancer for years. One deciduoid mesothelioma patient, for example, survived 60 months after diagnosis.