The period of time between a person’s exposure to asbestos fibers and the development of mesothelioma is referred to as its latency period. There are several asbestos-related diseases, but mesothelioma has the longest latency period. Typically 35 to 40 years will pass between exposure and diagnosis; however, cases have been diagnosed in as few as 20 or as many as 50 years after exposure.
As a general rule, the greater the asbestos exposure, the shorter the latency period. The average age of a patient diagnosed with malignant pleural mesothelioma is between 40 and 69. In patients diagnosed under age 40, usually childhood exposure has occurred. Mesothelioma in a child is so rare that medical professionals have blamed environmental exposure.
The long latency period of mesothelioma is a huge contributing factor to the poor prognosis associated with the disease. As with all forms of cancer, the earlier mesothelioma is discovered means a better opportunity for treatment. Unfortunately, like cancers such as those of the ovary or lungs, mesothelioma symptoms are typically unnoticed until the advanced stages.
Mesothelioma can initially manifest in a variety of body areas. One study found that, in 69 patients, pleural mesothelioma (chest) had a 35-year latency period, while peritoneal mesothelioma (abdomen) had a latency period of 28 years. Although exposure times can vary, the median duration of exposure associated with peritoneal mesothelioma is 11 years, while the exposure time associated with pleural mesothelioma is only five.
The overwhelming majority of mesothelioma cases are a direct result of occupational exposure. This exposure is now regulated in most of the developed world; however, due to the long latency period, new cases will continue to be diagnosed on a regular basis until at least 2020. Asbestos diagnosis statistics peaked approximately 30 to 40 years after the greatest asbestos usage occurred, which for America, was the 1960s. From approximately 2003 throughout the remainder of the decade, approximately 2,000 cases were diagnosed annually.
The pattern of mesothelioma statistics will change over the next 20 years due to the fact that average life expectancy is substantially longer than it was a few decades ago. Many individuals simply died before the disease could manifest itself. However, as of 2007, employees retiring at age 65 can now expect to live an average of 19.9 years for a woman and 17.2 years for a man. Furthermore, new asbestos regulations have significantly reduced the amount of exposure. Therefore, an increase in latency periods is expected.
However, recent events have shown exceptions to this trend. In the aftermath of the September 11, 2001, attacks on the Word Trade Center, many first responders and New York residents were exposed to airborned asbestos from the wreckage of nearby buildings. One paramedic by the name of Deborah Reeve helped in the recovery effort, but began having respiratory problems two years later. She was soon diagnosed with mesothelioma and passed away in March of 2006. Brief latency periods such as this are extremely rare, but they do happen.
Prior to the regulation of asbestos, the families and spouses of those working with asbestos were exposed to fibers carried home on clothing. Any family member that came into contact with the clothing or hair of a person working asbestos could have also been exposed.
The time frame of exposure can be hard to pinpoint due to the long latency period. A person may have worked a summer building construction job for a few weeks before the danger of asbestos was discovered. Enough exposure might have occurred to result in the presence of mesothelioma many years later, however, the person may not remember this short duration of exposure in his youth. This makes latency statistics challenging, but researchers will continue to work towards new treatments, as well as an eventual cure.