Dr. James Stevenson, M.D.
What is the Mesothelioma Latency Period?
Latency period is the time between exposure to something that can cause disease, like asbestos, and presentation of symptoms in patients. For mesothelioma specifically, there is a long latency period, which is directly related to the poor prognosis that is typical of the disease. Most mesothelioma patients experience at least a 20-year latency period, though there have been reports of mesothelioma developing between 10 and 70 years after initial asbestos exposure.
Due to the long latency of the disease, the impact from asbestos regulations may not be felt for decades. Without a complete asbestos ban in the United States, it will take years for the harmful impacts of asbestos exposure to decrease.
Factors that Impact Mesothelioma Latency Period
There are various factors that impact the latent period a patient may experience after exposure. Risk factors include age when first exposed, exposure level and gender, among others. Each of these factors contribute to the length of time before symptom manifestation, as well as the severity of the mesothelioma risk.
Duration and Concentration of Asbestos Exposure
The duration and concentration of asbestos exposure, commonly referred to as the dose response, are believed to be two of the main factors impacting the latency period of mesothelioma. According to a 2014 study, latency period and exposure duration are inversely related. If exposure occurs over a long period of time, the more likely it is that mesothelioma will develop sooner than average. Similarly, the more concentrated the asbestos fibers are when a person is exposed, the shorter their latency period tends to be. Exposure in poorly ventilated and enclosed areas create the most high-risk situations.
Male and female patients have been found to have different latency periods, which is just one of several differences between mesothelioma in women and men. According to research conducted in Australia, women tend to have longer latency periods than their male counterparts. The researchers found that of the participants, 81% of the female patients developed peritoneal mesothelioma 40 years after initial exposure, while only 46% of the male patients had a 40-year latency period. The average latency period for the male peritoneal mesothelioma patients was between 30 and 40 years. The majority of female cases weren’t diagnosed until 50 or more years after their initial asbestos exposure.
There is controversy around if this longer female latency period is due to a gender-specific difference. Some believe the disparity stems from women more often experiencing shorter durations of exposure and less concentrated airborne asbestos than men. In a retrospective study analyzing male and female patients, both of which had experienced occupational asbestos exposure, researchers found that female patients had a 29% longer latency period than the male patients. This result alludes to a primary gender basis for the latency difference.
Occupational asbestos exposure has been shown to lead to longer durations of exposure and higher concentrations of asbestos fibers than secondary or environmental exposure. There are a number of occupations that carry elevated risk of asbestos exposure due to the high levels of the mineral used across many industries.
|Average Latency Period by Occupation|
|Occupation||Average Latency Period|
|Dock Workers||35.4 years|
|Shipyard Workers||49.4 years|
|Maritime Workers||56.2 years|
Researchers have found that for certain occupations, latency period may be shorter than average because of the frequency and concentration of exposure on the jobsite.
An Italian study examined more than 400 cases of malignant pleural mesothelioma, specifically investigating the patients’ occupations. They found that when patients were organized by occupation, there was a vast disparity in the latency period of disease. Among the cases they reviewed, insulators had the shortest latency with an average of 29.6 years. The longest latency period, 56.2 years, was among maritime workers.
Other studies have found similar results in average latency periods following occupational exposure. According to a retrospective study of more than 1,000 occupational mesothelioma cases, more than 99% of the patients experienced a latency period of more than 15 years. Additionally, more than 96% experienced at least 20 years before the manifestation of symptoms.
Age at First Exposure
While people may experience asbestos exposure at any age, the onset of symptoms can vary widely, depending on how old the patient was when the exposure occurred. Patients who experience their first exposure to asbestos at an advanced age typically have shorter latency periods. Of patients analyzed in one study, those aged 20 – 29 at the time of first asbestos exposure had a 6% shorter latency period than those exposed prior to age 20. Those exposed to the mineral before age 20 had a median latency period of 40.6 years. The median latency period for study participants exposed at age 20 – 29 was 34.5 years.
Mesothelioma Types and Co-Occurring Disease
Research has found that the latency period varies between the different types of mesothelioma and is also impacted by the presence of co-occurring disease. For instance, peritoneal mesothelioma patients tend to have shorter latency periods than those with pleural mesothelioma. According to one study, the median latency period for peritoneal mesothelioma is 8.2 years, while pleural mesothelioma has a median latency period of 22.9 years.
Additionally, studies have found that the risk of developing certain types of mesothelioma can change depending on the amount of time since initial exposure. One study analyzing data from more than 20,000 mesothelioma cases found that the risk of pleural mesothelioma decreases after 45 years following first asbestos exposure. At the same time, researchers noted that the risk of peritoneal mesothelioma continues to increase regardless of number of years since first exposure.
Co-occurring diagnoses will also impact a patient’s latency period. Patients who had both pleural and peritoneal mesothelioma had shorter than average latency periods. Those with both peritoneal and pleural forms of mesothelioma had an 83% shorter latency time ratio than those with only one form of the cancer. Patients who have asbestosis (a chronic lung condition) in addition to mesothelioma have an average 5% shorter latency period than those without the condition, which equated to symptoms manifesting about two years earlier than in patients without asbestosis.
Resources for Mesothelioma Patients
Diagnostic and Prognostic Challenges Related to Mesothelioma Latency
The decades-long latency period of the cancer increases the difficulty of an accurate mesothelioma diagnosis. With the passage of time, patients may forget to divulge previous asbestos exposure to their healthcare team, which leads to inaccurate medical histories. This is especially common in those who experienced non-occupational asbestos exposure. The doctor’s work history prompt may not help this specific group recollect their contact with asbestos.
Additionally, the latency period allows ample time for the cancer to grow and progress to the later stages before intervention. Once metastasis occurs, there are often fewer viable treatment options for patients. The latency prevents administering treatments early, when more aggressive options like surgery are still feasible. Using more aggressive treatment options earlier has been directly connected with improved patient survival and longer life expectancy. As a result of the latency period, mesothelioma is often diagnosed in the later stages.
Due to the latency period and severity of mesothelioma, it’s vital that those who have experienced asbestos exposure are diligent about medical check-ups, and alert healthcare providers if any mesothelioma symptoms manifest.