Five Types of Mesothelioma: Testicular Mesothelioma In this blog series, five mesothelioma types and their causes will be examined. Some mesothelioma types are rarer than others. The first covered in this series is the rarest: testicular mesothelioma. Mesothelioma is a rare cancer with nearly 3,000 new cases diagnosed each year. The National Cancer Institute (NCI) defines mesothelioma as a type of cancer in which malignant cells are found in the chest or abdomen lining, called the mesothelium. The disease can also affect the lining of the heart and abdominal cavity. However, there are little known and even rarer types of mesothelioma that affect the lining of other organs in the body. One such type is testicular mesothelioma. Testicular mesothelioma is the rarest form of the disease, with fewer than 100 cases reported to date, according to the American Cancer Society (ACS). Testicular mesothelioma is thought to develop in the membranous lining that surrounds the testicle, which is called the tunica vaginalis. This lining contains mesothelial cells — the cells in which asbestos fibers lodge. An alternative theory proposes that mesothelioma may occur in the testicles through the serosal surface of the tunica, on which firm, yellowish tissue can be found encasing the scrotum and thickening the tunica vaginalis. Uncontrolled growth of the cells in this tissue can lead to the formation of tumors. Testicular mesothelioma, when diagnosed, was primarily found as a secondary tumor to an initial occurrence in the abdominal area of the body. For this reason, treatment of testicular mesothelioma must address both the primary and secondary tumors and may involve surgeries to remove the tumors as well as part of the testicles. It has long been known that inhaling asbestos fibers can cause mesothelioma decades later. The explanation for how inhaled asbestos could lead to tumors in the testicles is still theoretical. What is known is that both testicular mesothelioma and peritoneal mesothelioma — another rare type of the disease — are usually fast-spreading, aggressive types of cancer that are difficult to treat. In the next installment of this five-part blog series, epithelial mesothelioma will be addressed.