Mesothelioma Latency Period

The long period of time between exposure and illness is one of the hallmarks of mesothelioma.

It is very rare to have a latency period of less than 15 years, while the longest is around 60 to 70 years. The latency 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 asbestos they were exposed to.

An overwhelming majority of people diagnosed with mesothelioma and other asbestos-related diseases are in their 60s or 70s. They were exposed to asbestos in the workplace as adults and it took decades for their cancer to develop. Those diagnoses come after common symptoms of the disease — persistent cough and 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.

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 begins experiencing symptoms that lead to a diagnosis.

Factors that Impact Latency Period

Recent studies conflict on what affects latency period and what is merely associated, but most research agrees that the duration and intensity of exposure have a direct impact.

Dose-Response Relationship with Latency Period

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 mesothelioma from short-term, high-level exposure.

One paramedic worked near the World Trade Center for several months after Sept. 11, 2001. Although she had no other known exposure to the toxic 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 it was shortest in insulation workers, who experienced an average latency period of slightly less than 30 years.

Fiber Type

Shorter latency periods are observed among people exposed to crocidolite asbestos. For example, workers and residents of the crocidolite mining district of Western Australia exhibited substantially shorter latency periods compared to people exposed to other fibers.

Occupation

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:

Insulation
Boiler maintenance
Shipyards
Factories
Power plants
Textile mills
Asbestos mining and processing

Secondhand Exposure

Secondhand asbestos exposure happens when someone directly exposed to asbestos accidentally exposes others to asbestos fibers remaining on their body or their clothing.

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, the National Institute of Occupational Safety and Health told Congress 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.

Characteristics Associated with Latency Period

Certain characteristics of mesothelioma are correlated with the disease’s latency period. For example, the cancer’s location and a patient’s age and gender are associated with varying latency periods.

Cancer Location

Some researchers estimate the latency period is longest for pleural mesothelioma — about 30 to 50 years — while latency period for peritoneal mesothelioma typically falls between 20 and 40 years.

However, research is relatively inconclusive. 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.

Gender

The study also reported that women have an average latency period of 53 years, five years longer than men. Other studies similarly found women have longer latency periods.

Researchers hypothesize this is a result of overall lower exposure levels in women. Historically, men have been exposed to asbestos while working in occupations such as construction, power generation and manufacturing. These jobs exposed workers 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 that lasted for shorter periods of time, which is associated with longer latency periods.

Age

Some researchers suspect age at the time of exposure may impact latency, but there are no studies investigating the science behind the potential connection.

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, the theory goes that 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 a diagnosis.

Latency Period and Diagnosis

Symptoms of mesothelioma — such as shortness of breath, chest pain and fatigue — may not appear until the cancer is in later stages. 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 significantly contributes to late-stage diagnosis. For example, mesothelioma often doesn’t cause noticeable symptoms until stage 3. By then, the cancer has spread into the chest cavity and is more difficult to treat.

This delayed onset of symptoms and late diagnosis is what most contributes to a poor mesothelioma prognosis for many people. Patients have the greatest chance at long-term survival when they are diagnosed in earlier stages of the disease and receive aggressive treatment aimed to put the cancer into remission. Treatments are more effective before cancer growth has spread, meaning an aggressive treatment plan has the greatest chance to work when administered early in the cancer’s development.

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.

Latency Period Research

Some researchers believe the latency period of mesothelioma actually could be greater than the typically observed 20 to 50 years. They suggest that if people had naturally longer life spans, more cases of mesothelioma would develop if given the time.

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.

However, people are now outliving the life expectancy of prior decades by about 10 years. In 1960, the average life expectancy was 69 years. The current life expectancy in the U.S. is around 78 years. From 1999 to 2008, 62 percent of new mesothelioma patients were 70 years or older.

As life expectancy continues to rise, researchers expect to observe correspondingly longer latency periods among mesothelioma patients.