Mesothelioma is an aggressive cancer related to asbestos exposure. Mesothelioma has a long latency period with 20 to 50 years passing between exposure and cancer development.
Mesothelioma Latency Period
The latency period of a disease is the time between exposure to a substance and the development of the disease symptoms. Mesothelioma has a very long latency period and patients may have been exposed to asbestos 20 to 50 years before mesothelioma symptoms develop.
Diseases like mesothelioma that have such a long latency period can make it difficult for the disease to be diagnosed as physicians and patients may mistake symptoms for those of other diseases.
Basic Factors of Mesothelioma Latency Period
Mesothelioma is caused when the needle-like fibers of asbestos are inhaled or ingested and lodge in body tissues such as the lungs or abdomen. Most people who are diagnosed with mesothelioma were exposed to asbestos through an occupation such as pipefitting, steel work or ship building but household members may also develop mesothelioma through secondary exposure. There are some basic reasons for latency time to vary including:
- Amount of exposure
In most cases, the amount of asbestos exposure is inversely related to the latency time. Greater exposure will commonly result in a shorter latency time but in some cases however, there is no definitive correlation.
- Length of exposure
People who worked for a long period of time in occupations that used asbestos for insulation or construction, may have had greater exposure and may have a shorter latency period.
- Type of exposure
Family or household members of those who experienced direct exposure may have also been exposed. This “secondary” exposure may have occurred when fibers were transported on contaminated clothing or footwear. These patients may experience a longer latency period.
Why the Mesothelioma latency period is so long?
Mesothelioma has one of the longest latency periods of any disease. The time between exposure and development of cancer can be 20 years or more with an average of 40 years. This is likely due to the nature of asbestos and its alteration of cellular behavior.
Asbestos fibers are thin, needle-like fibers which are also brittle. The substance was mined and pulverized to be shaped into insulation. The powdered asbestos contains very small asbestos fibers which, when inhaled or ingested (through the mouth), lodge in body tissues.
Unlike other types of chemical exposure, asbestos does not “poison” body tissue. Rather than entering cells, the asbestos fibers “lodge” or stick into the cellular membranes. Over a long period of time, the asbestos fibers causes inflammation in the tissues. This inflammation will ultimately cause cells to become damaged, resulting in DNA mutations. As DNA controls cellular behavior, the mutations cause the cells to start dividing uncontrollably, resulting in tissue growth and tumor formation.
Mesothelioma latency period is generally described as 20 to 50 years. Though a few patients may develop the disease more quickly, the average latency period is actually about 40 years and only 4 percent are diagnosed within 20 years of exposure.
Causes of Mesothelioma Latency Time Differences
There are several factors which influence the amount of time between asbestos exposure and mesothelioma disease development.
- Concentration of exposure
The concentration of the asbestos fibers that were inhaled or ingested plays a role in how long the mesothelioma latency period will be. In general, a person exposed to a greater volume of asbestos dust, will have a shorter latency time. Examples include: those who work in demolition or those who are involved in demolition clean-up, particularly when no breathing apparatus was used.
- Length of exposure
The longer the asbestos exposure period was, the shorter the latency time is likely to be. The average mesothelioma patient experienced 3.75 years of exposure. Someone who worked in an asbestos-related occupation for many years may have a shorter latency time than a person who was only employed in such a job for one year.
- Total exposure
The total amount of asbestos exposure is a combination of concentration and length of time. Asbestos that is inhaled or ingested is difficult for the body to remove and the more asbestos that is inhaled, the faster the disease may develop.
- Asbestos type
Asbestos is a naturally occurring mineral which is found in deposits in many regions of the world. There are several types of asbestos that can be is mined and pulverized before being reshaped into other items such as pipe insulation, flooring tiles and automotive brake components. The type of asbestos that is inhaled may have an effect on mesothelioma latency period with the “crocodilite” type being the worst due to its brittle, thin, needle-like characteristic which becomes easily airborne.
Other Factors Affecting Mesothelioma Latency Time
There are other factors which do not at first appear to be related to the amount or type of asbestos exposure. Each of these factors, however points to increased risk of mesothelioma development and differences in latency time for certain groups.
Gender also may play a role in latency time but the difference may be caused by exposure amount. Men are diagnosed with mesothelioma ten or more times more frequently than women and have a shorter average latency time. Women are also more likely to be diagnosed at an earlier stage and tend to have longer life expectancy and greater survival rates.
These differences are likely because fewer women experienced large amounts of exposure through occupation, particularly over a long period of time. Women are more likely to have had secondary exposure in the home and may have inhaled or ingested a lower amount of asbestos.
Cells which can be considered “cancerous” are present in everyone. For a variety of reasons, the DNA of individual cells may mutate but cancer does not develop unless the cells are allowed to divide uncontrollably. Younger people tend to have a longer latency time than those exposed at later periods in life. This may be due to:
- Better immune functioning in younger persons, allowing for the body to rid itself of mutated cells.
- Less exposure to environmental or lifestyle hazards such as smoking, toxins, excessive sun exposure or others which are known to increase the chance for DNA mutations.
- Declining health due to aging may make it easier for mesothelioma to develop sooner
Rates of mesothelioma have been rising over the past decades. This may be due to increases in life expectancy, which have allowed for more time for mesothelioma to develop in each patient. As a person ages, their risk of mesothelioma continues to rise, even if asbestos exposure was many years before.
The specific occupation may have an impact on mesothelioma latency time. Though asbestos was used in many industries, certain occupations tend to have shorter mesothelioma latency periods. This is related to total exposure, along with other factors such as breathing rate and lack of air filtration.
Mining has always presented a multitude of occupational risks, including risk of asbestos exposure in certain areas.
- Miners often worked in confined areas, with little air circulation and no breathing equipment
- Miners often have increased respiration rates due to poor air quality and increased physical demand
- Food consumed at or even within the mine site may have been contaminated with asbestos dust, leading to ingestion of the substance
- Asbestos deposits may be near or mixed with other minerals, resulting in inadvertent exposure
Occupations which are more physical demanding may also have a shorter latency time due to increased respiratory rates.
- Shipyard workers
- Construction workers
- Steel workers
Though firefighters wear breathing apparatuses when entering a burning building, they do not do so during most of their fire-fighting or rescue work. Steel workers, pipe fitters, ship builders and construction workers were not likely to have ever used air filtration.
Delayed Diagnosis due to Mesothelioma Latency Period
In general, greater asbestos exposure results in a shorter mesothelioma latency time but each case is unique. In every patient however, the long latency period and rarity of mesothelioma presents a significant problem with diagnosis. Symptoms of mesothelioma generally mimic other conditions, each of which will likely be considered first.
Delayed recognition of symptoms may result in mesothelioma not being diagnosed until a later stage of the disease. This can make treatment more difficult and may result in a poorer prognosis. Getting a second opinion and seeking the attention of a mesothelioma specialist can help to increase treatment options and improve prognosis.