The latency period refers to the time between initial asbestos exposure and when a doctor definitively diagnoses the cancer. The long period of time between exposure and illness is one of the hallmarks of mesothelioma.
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The typical mesothelioma latency period is 20 to 50 years, with recent studies finding a median of 30 to 45 years. Under normal circumstances, the shortest possible latency period is 10 to 15 years, while the longest is more than 50 years. The time period depends on a number of factors such as the duration and intensity of asbestos exposure, as well as the patient’s gender and the type of mesothelioma. Because of this long time span, most people diagnosed with mesothelioma and other asbestos-related disease are in their 60s or 70s. Those diagnoses come after symptoms of the disease — persistent cough or difficulty breathing — become nagging or debilitating.
Studies show lower exposure levels and shorter durations of exposure can lead to longer latency periods. Conversely, individuals with high levels of exposure for long periods of time have significantly shorter latency periods.
The latency period ends when symptoms finally begin and a doctor can diagnose the patient. For most illnesses, a latency period begins when an individual is exposed to a virus or another illness-inducing entity and ends when the person first begins experiencing symptoms. Although some experts use this definition for mesothelioma latency period, most agree this asbestos-related cancer is considered latent until it is actually diagnosed.
This is because symptoms of mesothelioma can actually arise before a patient has the cancer. Asbestosis, a non-cancerous illness caused by asbestos, has many of the same symptoms and some people with asbestosis go on to develop mesothelioma. So a person diagnosed with asbestosis could have mesothelioma-like symptoms such as a persistent cough and chest pain before the cancer manifests itself.
At later stages of development, the cancer is more difficult to treat and the patient generally has a shorter life expectancy. But a prompt diagnosis followed by immediate treatment can lead to an improved prognosis.
Recent studies conflict on the matter of what affects latency period, but most research agrees that cancer location and type of exposure can have an effect. Studies have also found that higher doses of the substance result in shorter latency periods.
Exposure to extremely high levels of asbestos can lead to a shorter mesothelioma latency period, even if the duration of exposure is only a few months. Because of this, individuals at risk of having the shortest latency periods include first responders. Some paramedics, firefighters and police officers who worked immediately after the World Trade Center terrorist attacks and during Hurricane Katrina have already developed asbestos-related mesothelioma from short-term, high-level exposure.
One paramedic worked near the World Trade Center for several months after September 11, 2001. Although she had no other known exposure to the mineral, she died from the disease less than five years later.
As years pass, medical experts expect to see an elevated amount of these cases in first responders. Many of these new patients are expected to have abnormally short latency periods, putting them among the 1 percent of mesothelioma patients who receive a diagnosis within 15 years of initial exposure.
Like exposure to high levels of asbestos, exposure for longer periods of time can also shorten the expected latency period. Consequently, people with a history of heavy occupational exposure typically experience shorter-than-average latency periods. One study found that it was shortest in insulation workers, who experienced an average latency period of slightly less than 30 years.
More than 75 occupations put workers at risk of asbestos exposure. Of these occupations, certain ones exposed workers to high concentrations of asbestos. People with extensive exposure to asbestos — whether through short-term, high-concentration exposure or long-term moderate-concentration exposure — may exhibit shorter latency periods.
Some of these high-risk occupations include jobs in:
Secondhand asbestos exposure happens when someone directly exposed to asbestos accidentally exposes others to asbestos fibers remaining on their body.
People who work with asbestos may bring the toxic fibers home on a regular basis, posing a threat to household members. This results in low-level asbestos exposure that is associated with longer latency periods than direct, heavy exposure.
In 1995, National Institute of Occupational Safety and Health told Congress that the health effects of household asbestos contamination were real and serious. They reported on family members who developed mesothelioma, lung cancer, ovarian cancer, gastrointestinal cancer, asbestosis and other lung conditions.
Some researchers estimate that the latency period is longest for pleural mesothelioma, about 30 to 50 years, while latency period for other types typically falls between 20 and 40 years. But a 2011 study reported a statistically insignificant difference in latency periods. In the study of 238 mesothelioma cases, researchers found a latency period of 49 years for pleural mesothelioma and 46 years for peritoneal mesothelioma.
The study also reported that women have an average latency period of 53 years, five years longer than men. Other studies similarly found that women have longer mean latency periods. Researchers hypothesize that this is a result of overall lower exposure levels in women. Historically, men have been exposed to asbestos while working in lines of work such as construction. These jobs exposed them to heavy concentrations of asbestos for long durations. Conversely, women were most often exposed secondhand, such as when handling their husbands’ work clothes. These were lower exposure doses which lasted for shorter periods of time.
Some researchers suspect age at the time of exposure may impact latency. The immune system functions less optimally as people age. Theoretically, the older someone is at the time of exposure, the harder it could be for the body to eliminate asbestos fibers or control the damage they cause, potentially leading to shortened latency.
For example, someone heavily exposed in their 40s or 50s could potentially develop mesothelioma within two decades instead of the typical three to five. It is challenging to pinpoint age as a factor in asbestos disease latency because it usually takes decades for asbestos to cause damage that leads to disease.
Symptoms such as shortness of breath, chest pain and fatigue may not appear until the cancer is in later stages. Even after symptoms do appear, asbestos exposure may be overlooked as a factor. Because asbestos exposure occurred so long ago in most cases, many patients overlook it when considering possible causes of their illness. They may ignore chest pain or difficulty breathing and assume these common symptoms are caused by something minor. In some cases, this could delay an accurate diagnosis, allowing the disease more time to progress.
Aside from the long time it takes for asbestos to cause disease, delayed onset of symptoms can contribute to late-stage diagnosis. For example, mesothelioma usually doesn’t cause noticeable symptoms until stage III. By then, the cancer has spread into the chest cavity and is more difficult to treat.
This delayed onset of symptoms is what most contributes to a poor mesothelioma prognosis for many people. Patients have the longest expected life spans when they are diagnosed in earlier stages of the disease. Treatments are more effective before cancer growth has spread, so an early treatment plan makes a greater impact in lengthening life span.
Seeking a second opinion from a mesothelioma specialist is highly recommended. These doctors have the most experience and use the latest treatment options to extend survival.
Some mesothelioma researchers believe the actual latency period of mesothelioma actually could be greater than the typically observed 20 to 50 years. They believe that the typical latency period appears shorter because of people's already-limited life spans.
In the past, an asbestos-exposed individual may have died of old age or unrelated health problems before the illness had sufficient time to develop. But individuals are now outliving the life expectancy of decades past: Life expectancy in the United States in 2003 was 78 years, nearly a decade more than the life expectancy of 40 years earlier.
This has resulted in a greater occurrence of the cancer in older individuals. From 1999 to 2008, 62 percent of new mesothelioma patients were 70 years or older. While they now live long enough to see the cancer fully develop, similarly exposed individuals of previous generations may have died before the cancer had sufficient time to manifest itself.
It is expected that as modern life spans become longer, the mean and median observed latency periods for the cancer will become longer. As life expectancy continues to rise, researchers expect to observe correspondingly longer latency periods among mesothelioma patients.
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