Omental mesothelioma is a rare occurrence, a cancer that arises in the mesothelial cells of the omentum. The omentum is a layer of fatty tissue that overlays abdominal organs and plays a role in the immune system. While peritoneal mesothelioma often invades the omentum, primary cancer here is extremely rare.
What Is the Omentum?
The omentum is a layer of tissue that hangs like an apron over the front of the abdominal cavity. It develops out of mesothelial cells, which make up the mesothelium in other parts of the body. The omentum consists of two layers of mesothelial tissue with fatty tissue, connective tissue, and many blood vessels in between them.[1]
While the layer of fatty tissue over the abdomen may provide some warmth and protection for essential organs, researchers have found out that the omentum has several important roles:[1][2]
- The omentum has several areas known as milky spots, which contain immune cells.
- Abdominal fluid circulates through the milky spots, which act as filters.
- The omentum adheres to foreign bodies, such as catheters, which can cause problematic blockages. This also helps seal off areas of inflammation or infection.
- When inflammation and infection occur, the immune cells in the omentum respond, destroying bacteria and foreign bodies.
- The milky spots provide immune cells to the abdominal cavity.
- The omentum stimulates the growth of blood vessels in the abdominal cavity to promote healing. Omental tissue can be used as grafts in other parts of the body to stimulate this growth.
Cancer in the Omentum
Malignancies arising in the omentum are rare. However, it is a site of metastasis for cancers like ovarian and gastric cancer. It might even promote the spread of cancer.
Because the abdominal cavity fluid circulates through the omentum, cancer cells can get trapped, proliferate, and quickly develop new tumors.
What Is Omental Mesothelioma?
Omental mesothelioma occurs when a primary tumor develops in the mesothelial cells of the omentum. It is extremely rare and has only been described in individual case studies. Peritoneal mesothelioma typically invades the omentum, but the cancer rarely originates there.[3]
Are Omental and Peritoneal Mesothelioma the Same?
These are similar cancers in similar locations, but they are not the same thing. Omental cancer is not a subtype of peritoneal mesothelioma, the type of mesothelioma that originates in the peritoneum.
Omental mesothelioma involves mesothelial cells, but the tumors originate in the omentum. This is the main difference between it and peritoneal mesothelioma.
They have many similarities, though, including symptoms. Like the omental form, peritoneal mesothelioma has a poor prognosis, short life expectancy, and no cure.
Symptoms of Omental Mesothelioma
With so few cases of this cancer recorded, usual symptoms are difficult to determine. Individuals in case studies had the following symptoms:[3]
- Abdominal pain
- Back pain
- A tender mass in the abdomen
- Fluid buildup in the abdomen, known as ascites
- Weight loss
Diagnosis and Treatment of Omental Mesothelioma
The rarity makes it difficult to determine the best way to diagnose or treat this cancer. Misdiagnosis is common. Diagnosis follows the same steps as any cancer or mesothelioma, beginning with a physical exam.
Imaging scans and biopsies follow this to confirm malignancy and examine the cells to find the cancer type and area of origin of the primary tumor. Some patients may first receive a diagnosis of a different kind of cancer, such as peritoneal mesothelioma.
Immunohistochemistry is essential for accurate diagnosis. Pathologists use this strategy to look for markers and to distinguish rare mesothelioma from other types of cancer.
Treatment depends on each case, but in the few patients studied, surgery was the primary treatment strategy. Some patients reported in case studies had the omentum removed and recovered. For others, the cancer was too widespread, and surgery could not eliminate all the tumors.
As with peritoneal mesothelioma, those with cancer in the omentum can benefit from palliative treatments: paracentesis to train uncomfortable fluid buildup, pain management, or surgeries to remove some of the cancerous tissue.
A Rare Case of Secondary Omental Mesothelioma
One case study exists of a patient who developed secondary omental mesothelioma after first being diagnosed with pleural mesothelioma. The pleural type of this cancer is aggressive and metastasizes readily but not commonly into the abdomen or the omentum.[4]
The case had several unusual features, including the fact that the man had never come into contact with asbestos. It is the first and only described case of pleural mesothelioma secondarily infiltrating the omentum.[4]
The man received treatment for pleural mesothelioma and had a stable disease for six months. Then, the cancer spread to the right side of the pleura. Eleven months after that, he had abdominal symptoms, including pain and fluid buildup. An ultrasound showed a mass in the omentum.[4]
When doctors performed a biopsy to get a sample of fluid and tissue, they confirmed that the mass was secondary mesothelioma. The cells showed the same pathology as those in the primary cancer.[4]
A Rare Case of Mesothelioma of the Omentum and Liver
Yet another extremely rare example of omental mesothelioma is found in just one case study. This involved a woman, just 36 years old, who presented with abdominal and back pain. Doctors found masses on the liver and the omentum.[5]
Pathology studies of the biopsied cells found that they both originated in the mesothelium. Unusual for mesothelioma, the cells were not rapidly dividing.
The woman received a diagnosis of low-grade mesothelioma of the liver and omentum. Six months after surgical removal of the tumors, the woman showed no recurrence of cancer.[5]
What Is the Prognosis for Omental Mesothelioma?
The case of the woman who survived liver and omental cancer is rare. There are few cases to study, but overall, the prognosis for omental mesothelioma seems to be poor.
In one case report of a 70-year-old man, doctors diagnosed him with primary omental mesothelioma. It was advanced, and he died just three weeks after receiving the diagnosis.[6]
Omental mesothelioma is extremely rare, but it is possible and is probably associated with asbestos exposure. If you have exposure in your past, get screened regularly for any type of cancer.
